more port flow related info

grumpyvette · Oct 2, 2008

links, calculators and info well worth reading thru, yes theres a HUGE tendency to breeze over them, but they contain a ton of related info youll need

USE THE CALCULATORS, YOULL, QUICKLY FIND THE LIMITATIONS
http://www.rbracing-rsr.com/runnertorquecalc.html
http://www.wallaceracing.com/chokepoint.php
http://www.wallaceracing.com/header_length.php
http://www.users.interport.net/s/r/srweiss/tablehdc.htm

sellecting cylinder heads

you might want to watch this, its comparing the vortec SBC heads vs a CNC aluminum 210cc SBC head on a 383 (yes a head that large actually works and has a great deal more low and mid rpm torque that you may have been lead to believe, with 210cc ports and yes there are better heads in the...

garage.grumpysperformance.com

up to the rpm range where the port cross sectional area becomes a restriction to flow a smaller port is usually superior
for torque produced, larger ports tend to be less responsive and produce slightly lower torque so you need to match the flow to the displacement and rpm range

USE THE CALCULATORS to match port size to intended rpm levels... but keep in mind valve lift and port flow limitations[/color]
http://www.wallaceracing.com/runnertorquecalc.php
http://www.wallaceracing.com/ca-calc.php
http://www.wallaceracing.com/area-under-curve.php
http://www.wallaceracing.com/chokepoint.php
http://www.wallaceracing.com/header_length.php

CAM%20TIMING%20DIAGRAM%20BY%20CAMSHAFT%20ANGLE.jpg

keep in mind that the piston moves a great deal slower per degree of rotation
near the top and botton of the stroke than it does near the mid stroke in the bore, so thers more time for flow and presure to build per degree of crank rotation,making those areas of rotation more critical to performance

keep in mind the goal here is to increase or decrease the overlap , that occures as that has a major effect on the efficiency of the headers ability to efficiently scavenge the cylinders while both valves are simultaneously open

he chart below,is supposed to point out LSA, but its mis-labled

0810chp_05_z+comp_cams_camshaft_technology_insite_tech+lobe_separation_angle.jpg

port speeds and area

I frequently get asked "how do you select the correct port size and cylinder heads for any potential engine build" well it certainly helps to do your research, and the more you know the more likely you are to select the correct heads and matching components and knowing exactly what your trying...

garage.grumpysperformance.com

(LOBE SEPARATION ANGLE)
which can,t be changed once the cam is manufactured
LCA
(lobe CENTER ANGLE)
Which can be adjusted by advancing or retarding the cams index to the crank rotation, as desired
with bushings or an adjustable timing set.
keep in mind the goal here is to increase or decrease the overlap , that occures as that has a major effect on the efficiency of the headers ability to efficiently scavenge the cylinders while both valves are simultaneously open

http://www.howstuffworks.com/ignition-system.htm

A VERY USEFUL set of CALCULATORs
http://www.rbracing-rsr.com/runnertorquecalc.html

http://users.erols.com/srweiss/calccsa.htm

http://users.erols.com/srweiss/calcplv.htm

http://users.erols.com/srweiss/calcfps.htm

http://users.erols.com/srweiss/calcacsa.htm

Volumetric Efficiency: Is calculated by dividing the mass of air inducted into the cylinder between IVO and IVC divided by the mass of air that would fill the cylinder at atmospheric pressure (with the piston at BDC). Typical values range from 0.6 to 1.2, or 60% to 120%. Peak torque always occurs at the engine speed that produced the highest volumetric efficiency.
keep in mind as rpms increase so do port speeds and volumetric efficiency UP TO A POINT, WHERE THE TIME LIMITATION TO FILL AND SCAVENGE the cylinder limits power

as long as most of the cylinder pressure builds after the crank throw passes TDC, the pressure in the cylinder is used to push the piston down on the power stroke and make power, any pressure built before the crank rotation reaches TDC reduces power as it resists rotation, keep in mind at low rpms it takes about 30-50 thousands of a second to burn a cylinder of f/a mix, as the rpms increase the time required to burn the compressed mix decreases due to several factors like squish and turbulence, but at low rpms you don,t need a great deal of ignition advance because at 1000rpm your only getting 500 power strokes per minute per cylinder, or about 8 every second, so 6-8 degrees advance allows plenty of time to build pressure above the piston, and have most of it build after tdc in crank rotation.
increase the rpms to 3000rpm and youve cut the available burn time into less than a third, so ignition needs to occur sooner in the rotation, but as rpms continue to increase the flame pattern advance due to constantly being compressed faster and more violently, decreases the need for further increased ignition advance at some point, usually at about 3200rpm, where your ignitions usually fully advanced
read thru these

http://forum.grumpysperformance.com/viewtopic.php?f=70&t=967

http://forum.grumpysperformance.com/viewtopic.php?f=70&t=2798

http://forum.grumpysperformance.com/viewtopic.php?f=70&t=4683

http://forum.grumpysperformance.com/viewtopic.php?f=70&t=1015

grumpyvette · Oct 7, 2008

if you don,t read thru the sub linked info your missing a great deal of info those links contain

http://www.hotrod.com/techarticles/engine/hrdp_0802_chevy_intake_manifold_porting/index.html

http://garage.grumpysperformance.co...ber-of-people-that-don-t-use-resources.12125/

http://www.gofastnews.com/board/tec...-secrets-reduce-valve-shrouding.html#post5343

posting.php?mode=edit&f=52&p=1156

viewtopic.php?f=52&t=333

http://www.sa-motorsports.com/diyport.aspx

http://www.circletrack.com/enginetech/c ... index.html

http://www.circletrack.com/techarticles/general/139_0305_port_matching_engine_porting/index.html

http://speedtalk.com/shows/027_jim_mcfarland.html

http://www.chevyhiperformance.com/techarticles/95518_small_block_cylinder_head_porting/index.html

http://www.gmtips.com/3rd-degree/dox/tips/plen-port/port.htm

http://www.bfranker.badz28.com/96ss/58porting.htm

http://www.eecis.udel.edu/~davis/z28/buildup/plenum/

http://www.diyporting.com/molds.html

http://www.fordmuscle.com/archives/2006/12/MakingMolds/index.php

(1) open throat to 85%-90% of valve size
(2)cut a 4 angle seat with 45 degree angle .065-.075 wide where the valve seats and about .100 at 60 degrees below and a .030 wide 30 degree cut above and a 20 degree cut above that rolled and blended into the combustion chamber
(3)blend the spark plug boss slightly and lay back the combustion chamber walls near the valves
(4)narrow but dont shorten the valve guide
(5) open and straiten and blend the upper two port corner edges along the port roof
(6) gasket match to/with intake and raise the port roof slightly
(7) back cut valves at 30 degrees
(8) polish valve face and round outer edges slightly
(9)polish combustion chamber surface and blend edges slightly
(10) remove and smooth away all casting flash , keep the floor of the port slightly rough but the roof and walls smoothed but not polished.
(11) use a head gasket to see the max you can open the combustion chamber walls
(12) blend but don,t grind away the short side radias

ported sbc (POSTED BY http://www.maxracesoftware.com)

I read somewhere that using 1.6 rr adds to duration is there truth to this?

technically YES you add about 1-2 degrees effective duration,because the valve accelerates off its seat faster and the valves open both longer and a bit further off the seat, but look at the charts below, if measured even at .100 lift, the difference in duration is very minimal, but pragmatically the increase is so small its nearly meaningless in how the engine runs.
Higher ratio rocker arms may show more of a hp gain ,. You are gaining more of a flow "curtain" or window, more quickly, as the valve accelerates off the seat slightly faster with the higher ratio rocker,. In the case of the SBC many times the best gain is found by using 1.6:1 rockers on the intake side only, and retaining 1.5s on the exhaust. One thing to consider is that by using higher ratio rocker arms, you are also increasing the effective cam duration,very slightly and increasing the engines ability to breath marginally, but in most cases swapping to a larger cam and retaining the 1.5:1 RATIO ROCKERS HAS MORE POTENTIAL POWER, BUT THE 1.6:1 ratio swap is far easier to do and a good tuning tool.
AS A GENERAL RULE YOU WILL ALMOST ALWAYS GAIN MORE FROM, A SWAP TO A SIMILAR DURATION ROLLER CAM OR A SLIGHTLY TIGHTER LSA ROLLER CAM WITH ITS MORE AGGRESSIVE RAMPS THAN FROM A ROCKER SWAP ON A FLAT TAPPET CAM

notice the change in duration is minimal but the area under the lift curve has improved insuring the flow or curtain area has improved,

high-ratio-rocker-arms-install+graph.jpg

http://www.pontiacstreetperformance.com ... rArms.html

Higher Ratio Rocker Arms

by Jim Hand, July 1999

[This article originally appeared on Eric Douthitt's, The Pontiac Garage,
website. It now appears here courtesy of the author and Eric Douthitt.]

What are the overall effects of higher ratio rockers? Do they add stress to the engine? Are they safe to use? Do they add power? What precautions should be considered before installing them? The following is a summary addressing these questions.

The basic valve train consists of a cam, or cam lobe, some sort of cam follower, such as a lifter, a push rod, a rocker arm, and the valve (with the associated retainer/keepers, and valve springs). The cam lobe lift is dictated by the dimension from the base circle of the lobe to the lobe centerline, or peak of the lobe. The base circle must be kept large enough to not degrade the strength of the cam, while allowing for enough lift (in conjunction with the rocker arm) to meet all design goals. Obviously, the peak lift of the lobe cannot be higher then the outer diameter of the cam bearings - otherwise, the cam could not be installed. So, in cam design, as more lift is designed in, the base circle becomes smaller in diameter. As the obtainable lift is limited, the lift is multiplied by the rocker arm ratio to bring it up to the desired point(s). If we used rocker arms that had a 1 to 1 ratio, the valve would follow the exact opening and closing as the cam lobe - same peak lift, same opening and closing rate, and same limited valve open area. By making the rocker some greater ratio, such as the standard 1.5, the lift of the lobe is multiplied by 1.5, the opening and closing rates are much faster, and the area under the overall "curve" is much greater. This becomes very obvious by reviewing the graph.

The cam is rated at some duration at .050 lifter/tappet rise. This of course cannot be changed and will remain the same regardless of the rocker arm ratio. However, the valve lift is normally specified with standard 1.5 ratio rocker arms. This can be changed by installing different ratio rockers. As a 1.65 ratio rocker is 10% higher ratio then a 1.50, the lift provided by the 1.65 rocker will be 10 % greater with all cams. This also can be seen on the attached graph. Note that the graph shows a 1.72 ratio rocker, but the action is similar between various ratios. What happens to valve open time with the higher ratio rockers? Because the higher ratio rocker lifts the valve to a higher point in the same time period, it has to lift both quicker and steeper. As the valve begins to open at the same point regardless of rocker ratio, and it opens at the same time as the cam lobe, the duration of the valve opening in crankshaft degrees at the initial opening and closing points is identical to the cam lobe duration. However, because of the quicker and steeper opening/closing rates, the valve open time is greater from any point after initial opening when a higher ratio rocker is used. This is also obvious on the graph. How much more duration? I devised a method to actually measure it. As a standard lobe measuring point is .050 lifter rise, and lobe lifts are normally specified with 1.5 rocker ratio, that means the valve will always be at .075 when the lobe reaches .050" lift (when a 1.5 rocker is installed). By using the .075 point, and determining where it occurs in relationship to the crank in degrees, a yardstick is provided from which to reference any different rocker ratios. As expected, a higher ratio rocker will allow the valve to reach the .075 lift point earlier in the lift cycle (and later in the closing cycle). As the .075 valve lift point is the industry standard when specifying cam duration (1.5 standard rocker ratio X .050 tappet/lifter rise), it becomes a valid reference point. In the Wolverine 234 degree intake lobe, the intake valve was open 4 to 5 degrees longer when measured in reference to the crank when the larger ratio rockers were used. This is also easy to see on the graph.

Summary:

Higher ratio rocker arms open the valve faster, higher, and hold it open for a much greater total period of time as compared to lower ratio units. Does this cause more stress on the valve train? There will be more pressure on the cam lobes due to the friction and pressure caused by the higher lift and resultant greater spring load. However, as compared to providing the same higher lift and effective longer duration with a more radical cam and even stiffer springs, the higher ratio rockers may create less total valve train stress. And such a cam lobe would be very aggressive and would require much heavier springs to keep the lifter from flying off the lobe. Very radical lobes will also add more side stress on the lifters/bores and could possibly cause lifter bore failure. The added pressure on the studs from either higher ratio rockers, or more radical lobe, will be well within the capabilities of modern after market studs.

Safety:

Some precautions are needed when using higher lift rockers. The valve springs must be able to handle the increased lift. Otherwise, spring bind may occur and that will cause serious engine damage. On very high lift setups, or unusually tight lobe separation or advanced intake lobe cams, valve to piston interference must be checked. As the mechanical aspects of different ratio rockers vary, the position of the push rod in relation to the stud may change. Higher ratio units typically have the push rod depression in closer to the stud, and that may cause interference at the tops of the push rod holes in the heads. This clearance must be checked. Higher lift units may cause interference with the rocker covers. This problem can be handled with extra cover gaskets, cover spacers, or even special covers.

More Power? This is the really big question and the answer varies with different applications. As we know, an engine runs best within a given rpm range with an ideal cam - correct lift, duration, and lobe placement. If we have that ideal and perfect cam installed, higher ratio rockers will not help performance. In most cases, we don't have the ideal cam, and additional lift and/or additional duration might help performance. As it is quite easy to install rockers, providing all safety points mentioned above are met, direct testing can be conducted with any engine. I maintain and have proven to my satisfaction that higher ratio rockers can provide the same benefits as more exotic cams but without the excessive costs. The secret to any engine's performance is to obtain maximum area under the valve open curve with the minimum overlap and mildest valve train action, again assuming the open time occurs at the optimum time. High ratio rockers accomplish that due to their complex effect on the valve train dynamics. If we would compare two cams of equal duration and lobe positions, but one with more lift on the lobe and 1.5 ratio rockers, and the second with less lobe lift but higher ratio rockers to equal the lift of the first, the milder lift cam with higher lift rockers will always provide more performance (again providing the cam is not to large to begin with).

Rocker Arm Ratios:

Do not assume rockers are the actual rated lift ratio. Example: My Pontiac 1.5 flat rockers measure an average of 1.48, and a set of original Pontiac 1.65 rockers measure an average of 1.61. A set of 1.6 rated rollers from Jim Butler measured 1.61, and a set of Harland Sharp 1.65 rollers measure 1.75. All of these measurements were made with a lightweight checking spring, and do not represent actual ratio under the normal spring loads of 260 to 600#. We could expect these ratios to diminish as heavier springs are used. The representative from Harland Sharp states that the HS 1.65 Pontiac rollers are "only" 1.70 when measured with a 550# spring load. I suspect my stock push rods would do a real contortionist act with 550# valve springs, but we have to remember that the big rollers require this level of pressure.

more related info

http://www.wallaceracing.com/rockercalc.php

viewtopic.php?f=52&t=198

viewtopic.php?f=52&t=506

viewtopic.php?f=52&t=126

http://www.chevyhiperformance.com/techa ... index.html

http://www.carcraft.com/techarticles/11 ... ewall.html

http://www.popularhotrodding.com/tech/0 ... hrods.html

viewtopic.php?f=52&t=1070

viewtopic.php?f=52&t=181

viewtopic.php?f=52&t=82&p=105#p105

http://www.popularhotrodding.com/engine ... ewall.html

http://www.highperformancepontiac.com/t ... ewall.html

http://www.vetteweb.com/tech/0204vet_sm ... index.html

grumpyvette · Oct 9, 2008

http://www.gofastnews.com/board/tec...-secrets-reduce-valve-shrouding.html#post5343

one factor that gets discussed a great deal is the difference in port size or port CCs, the sad truth is that Id bet 90% of the discussions are just guys repeating stuff they have heard with zero real idea what they are talking about.
while theres generally some relation of port cross sectional area to the listed port CCs its NOT a direct linear relationship, and its the cross sectional area,shape, length and surface finish, of the whole intake runner not the cylinder heads, port CCs that matter to the air flow., and if the exhaust system can,t effectively scavenge the cylinders or the intake can,t supply the flow, or the cam duration and lift don,t match the intended port flow rates performance will suffer. you generally want the smallest high velocity port that matches your applications needs, and flow requirements, on a N/A application, on a supercharged application youve got some other factors and a slightly larger port is usually best.
remember the cam timing and exhaust scavenging also need to match to maintain the max efficient volumetric efficiency.
the most common mistake made by many people is that they fail to look at an engine as an interconnected group of component sub systems and they don,t realize that changes to a single component, no mater how much potential that component has is not going to allow that component or change in the potential to be realized until all the matched and supporting systems have similar potential.
EXAMPLE ,
the heads may be capable of flowing (x) on a stock engine but with careful selection of a cam with the correct duration and lift, and with a tuned header, and matching valve train mods along with some port and bowl clean-up the resulting improvements can be significantly more impressive.

http://garage.grumpysperformance.com/index.php?threads/is-backpressure-hurting-your-combo.495/

http://garage.grumpysperformance.co...alves-and-polishing-combustion-chambers.2630/

http://garage.grumpysperformance.co...e-springs-and-setting-up-the-valve-train.181/

http://garage.grumpysperformance.co...lsa-effects-your-compression-torque-dcr.1070/

http://garage.grumpysperformance.com/index.php?threads/more-port-flow-related-info.322/

http://garage.grumpysperformance.co...2-bbc-rebuild-but-think-things-through.13604/

http://garage.grumpysperformance.co...t-intake-on-oval-port-heads.13146/#post-69975

THINK IT THRU!
you don,t build an engine combo by selecting just heads, first and then matching the other components to that head flow rates, you select a hp/torque/rpm power band as a goal and then select the necessary components to slightly exceed that hp/torque/rpm power bands requirements knowing all parts NEVER work at 100% of the potential when matched in a combo.

Chad Speier posted this bit of info

" look at cylinder heads differently than most, I guess..

Size doesn't matter and I hate when someone says this head or that head is too big. It's all about matching the minimum CSA to the amount of air it is moving, then balancing the port from there.

So, here is how I look at it. BBC core such as this.

380cfm head needs a minimum of 3.25in²
400cfm head needs a minimum of 3.43in²
420cfm head needs a minimum of 3.60in²
440cfm head needs a minimum of 3.77in²
460cfm head needs a minimum of 3.95in²
480cfm head needs a minimum of 4.11in²"

heres free cam selection software to narrow your choices

just for grins put your info into this program, and don,t lie, and see what cam it suggests
http://www.camquest.com/

http://www.compcams.com/Pages/409/camquest-6.aspx

AS your displacement per cylinder increases the effective valve size per cubic inch decreases so you need a slightly tighter LSA , to allow more effective exhaust scavenging of the cylinder volume during the valve over-lap timing, and these charts should help.
but I must point out that the major reason you want that tighter LSA is to allow effective cylinder scavenging with the exhaust inertia helping to drag in the following intake charge as the low pressure at the exhaust port caused by the rapid exiting gases in the headers if the cam timing is correctly matched to the application draws gases into and partial out of the cylinder while both valves are open during the over lap period.
increasing the cam duration past a certain pint determined by several factors such as engine displacement, effective compression and header scavenging efficiency in a set rpm band is usually counter productive, as it tends to bleed off the next intake charge volume.
if done correctly this will increase the efficiency of the cylinder fill rates, and flush out a higher percentage of the remaining previously burnt exhaust gases.

0607phr_11_z+camshaft_basics+lobe_centerline_angle_determination_chart.jpg

I think this chart above is frequently either ignored or mis-understood
let me show an example
lets say your building a big block 496 with the typical oval port after market heads having 2.19' diam. intake valves and its got 10.7:1 compression.
a 496 displacement has 62 cubic inches per cylinder, if you look at the chart and divide 62 by 2.19 you get 28.3, look at the chart! that would strongly suggest a 100-102 LSA (LOBE SEPARATION ANGLE be selected,) GOOD LUCK FINDING A CAM FOR A BIG BLOCK WITH THAT LSA!

heres a chart I found that I don,t fully agree with, I think its a bit conservative, by about 3%-5% on the required cam duration ,required to avoid detonation with todays crappy octane fuel, but it at least gives you a base to work from, but Id suggest selecting a bit more duration

software like the free comp cams software below

http://www.compcams.com/Camquest/default.asp

you'll also find these links and sub links useful

ID suggest you select from heads from these sources
Jegs; 800/345-4545; Jegs.com

Summit Racing; 800/230-3030; SummitRacing.com

Scoggin-Dickey Parts Center; 800/456-0211; ScogginDickey.com

TRICKFLOW
http://www.trickflow.com/egnsearch.asp? ... 4294867081
http://www.trickflow.com/customerservice
1-330-630-1555 • 1-888-841-6556

BRODIX
http://www.brodix.com/heads/heads.html
479.394.1075

DART
http://www.dartheads.com/products/cylinder-heads
Dart Machinery; 248/362-1188; DartHeads.com

AIR FLOW RESEARCH
http://www.airflowresearch.com/
toll free: 877-892-8844
tel: 661-257-8124

Patriot Performance
Patriot Performance; 888/462-8276; Patriot-Performance.com

RHS
http://www.racingheadservice.com/rhs/cylinder-headshtml
Toll Free: 877-776-4323
Local: 901-259-1134

EDELBROCK
http://www.edelbrock.com/automotive_new ... main.shtml
Edelbrock; 310/781-2222; Edelbrock.com

BMP (world products)
http://www.theengineshop.com/products/cylinder-heads
Tel: 631-737-0372
Fax: 631-737-0467

TRJ
http://trjperformance.com/cylinder-heads-top-end-kits-components/complete-heads/

BUTLER PERFORMANCE
http://www.butlerperformance.com/products/cylinder_heads/cylinder_head_labor.html
866-762-7527

BLUE PRINT ENGINES
http://www.blueprintengines.com/ind...sb-chevy-aluminum-cylinder-heads-cnc-machined
1800-483-4263

PRO-FILER
https://www.profilerperformance.com/
937‐846‐1333

grumpyvette · Oct 20, 2008

there seems to be a HUGE mis-understanding about port size and how it potentially effects your engines torque range,
port size should be thought of more as a restriction to reaching necessary flow than a benefit to making a significant torque curve PROVIDED your matching the total engine component list to the intended rpm range and expected hp peaks the engine will be expected to produce and run at!
YOU GENERALLY WANT THE SMALLEST PORT SIZE THAT WILL PROVIDE THE NECESSARY FLOW REQUIRED
BUT its not port size but the ports cross sectional area and length matched to the other components like the engines displacement,compression, cam timing and bore/stroke ratio PLUS the exhaust systems designed scavage efficiency range at any give RPM level has a major effect on results, the size of the ports in your cylinder heads can be one of the least> THAT'S RIGHT I SAID CAN BE THE LEAST important of the factors that determine where in the rpm range your engine builds its best power, while its true that smaller port cross sectional areas due cause the airflow speeds to increase,, and that INCREASED PORT VELOCITY HELPS PACK YOUR CYLINDERS ,its also very true that the INTAKE MANIFOLD runner length and cross sectional area of the intake used, the compression ratio and the cam timing and the design of the header primary tubes are at least two to three times as important simply because they control the airflow thru the cylinder to a much greater extent, and the engines stroke and total displacement are extremely important, changing JUST the displacement and cam timing has a HUGE EFFECT on WHEN and HOW the airflow in the ports gets its vacuum signal and how the port responds to that change in pressure.
you can build a torque monster engine with large ports in the cylinder heads, quiet easily if the other factors are carefully matched

notice that the 180cc AFR heads which are known for torque production have basically the SAME cross sectional area as the TRICKFLOW 195 cc heads and that the difference between the AFR 180cc heads and the 210cc heads is only approximately a 6% increase in size so the true air flow thru a 210cc head will be only approximately 6% slower on the same engine.........swap to a 383 from a 350 which is approximately 8% larger and you quickly see where the smaller heads can become more of a restriction than a benefit to the combo!

know I know from experience building engines for years that a rough guide to matching hp to the intended engine port flow requirements can be guessed at fairly closely using these formulas below, play with them then measure the port cross sectional area in your engine at its narrow point, and don,t forget the cam lift your restricted too and the valves curtain areas in the combustion chambers

"Fortunately for our purposes, these complex calculations can be broken down into a very simple formula that is useful for us as speed crafters.
Intake Runner Area = Cylinder Volume X Peak Torque RPM / 88200
This formula takes into account the best theoretical speed that air can move down the runners, to give the best volumetric efficiency. Peak Torque occurs in an engine at the RPM where the engine is enjoying its highest volumetric efficiency. "

keep in mind those fancy advertised cylinder head port flow rates at lifts that exceed your cams lift are MEANINGLESS to YOUR engines performance if your intake port flow, is restricted ,if the exhaust headers won,t scavage the cylinders effectively,or you choose to use of a smaller cam, an intake design that restricts flow, a drive train that won,t allow the engine to operate at its ideal rpm band most of the time or a dozen other factors in the engines component selection, its the total combo not any one component that will make or brake your engines potential power curve.

below youll find some things to read/play with

http://www.n2performance.com/lectures/airflow.pdf

http://www.rbracing-rsr.com/runnertorquecalc.html

http://www.circletrack.com/enginetech/c ... index.html

heres a chart FROM THE BOOK,HOW TO BUILD BIG-INCH CHEVY SMALL BLOCKS with some common cross sectional port sizes
(measured at the smallest part of the ports)
...........................sq inches........port cc
edelbrock performer rpm ....1.43.............170
vortec......................1.66.............170
tfs195......................1.93.............195
afr 180.....................1.93.............180
afr 195.....................1.98.............195
afr 210.....................2.05.............210
dart pro 200................2.06.............200
dart pro 215................2.14.............215
brodix track 1 .............2.30.............221
dart pro 1 230..............2.40.............230
edelbrock 23 high port .....2.53.............238
edelbrock 18 deg............2.71.............266
tfs 18 deg..................2.80.............250

ON a supercharged combo,the larger port size in the heads not, likely to be a significant problem
the lack of low rpm port speeds, with larger heads that might be critical on an N/A combo to generate torque, with its superior low rpm volumetric efficiency, is just not that big a factor once you install a supercharger, and the difference in port cross sectional area is more of a restriction with smaller ports than helpful once, you've got over about 2500rpm-3500rpm depending on components selected , a supercharger changes a good deal of the factors that you'll need to look at more closely and negates several factors that in a N/A combo warrant more attention,(especially with a centrifugal, supercharger as they tend to increase in efficiency with the rpms) things like cam timing, and exhaust restriction play a far more important roll and use of a cylinder head with a larger port cross section, and n/a port flow rates get to be slightly less critical,to low rpm responsiveness and with the roots superchargers the low-mid rpm efficiency is far more likely to compensate for the larger port sizes lack of a ports N/A flow rates

http://www.dsmtuners.com/forums/turbo-s ... asics.html

AFR 195 Eliminators
actual cc's in the intake port.....184
cross section area...2.13 sq.in
Flow spec's.....281/221

AFR 195 comp Eliminators
actual cc's ....189
cross section...2.15 sq.in
Flow spec's...306/235

Trick Flow 195 K D
before porting actual cc's....185
after porting ...188
cross section....2.13 sq.in
Flow spec's....270/210

Edelbrock Etec 200's
actual cc's before porting N/A
after porting....197
cross section...2.13
Flow spec's...270/218

(flow spec's @ .600 lift)

Potential HP based on Airflow (Hot Rod, Jun '99, p74):
Airflow at 28" of water x 0.257 x number of cylinders = potential HP
or required airflow based on HP:
HP / 0.257 / cylinders = required airflow
SO HOW MUCH WOULD YOU LIKELY GAIN FROM A HEAD SWAP THAT ALLOWED YOUR HEAD FLOW ON A SERIOUS BIG BLOCK TO JUMP FROM LETS SAY 370CFM to lets say 425CFM?

A HARD number that has held pretty true for conventional BBC on gasoline , with compression ratios up ner optimum, near 12:1-13.5:1 to predict peak HP from head flow is .25-.27 x intake flow rate @ 28" x 8 (# of cyls). Like others have said, a lot of variables,like efficiency of exhaust scavenging,compression ratio and valve lift VS port potential flow, but it has been within 20 or 30 HP on several different BBC's I've seen being dynoed.

For example, I had an 357 AFR-headed 540, the heads flow 425cfm @ 28". So 425 x .27 x 8 = 918 HP. It made 940. Another motor calc'd at 1030, made 1040 on the dyno.

Using the same logic, 50 cfm x .27 x 8 = 108 hp. It's not that simple, it depends on combination, how optimized everything is etc. But if you are looking for round numbers, 50-75 hp is probably realistic, 100 hp possible

ITS A COMMON MISCONCEPTION,THAT YOU MEASURE PORT CROSS SECTION AT THE PORT ENTRANCE,BUT ITS NOT the port area at the entrance , you need to use in the calcs, ITS the MINIMAL port cross section at the SMALLEST point in the port, usually near the push rod area.
LIKE a funnel, its not the largest part of the opening but the smallest thats the restriction to flow
NO!ITS NOT FOOLPROOF! BUT ITS A VERY GOOD TOOL!
what tends to make me crazy is guys that insist on running vortec or similar small port heads and a dual plane intake for max low rpm torque, when I or someone elsae builds thier engine,who then come back and want thier 383-421 sbc to run the big hp/tq numbers and pull hard at 6000rpm and above where those small ports are far past there effective air flow limits
Ive built some KILLER engines useing the 215cc and 230cc IRON EAGLE heads and SIMILAR larger port heads that made great torque in the low and mid ranges, a dual plane intake,with long runners and a 600cfm-750cfm carb helps, as does a cam thats designed for the midrange torque, and full length headers , with 1 5/8" primairies,its NOT the port size in the cylinder heads ALONE that determines the results! its the COMPLETE MATCHED COMBO and the thought that was put into makeing the components match the intended power curve, and matching the cars rear gear and stall speed to that power curve, sure you might be running slightly higher average rpms, to get the best power ,but youll be making a whole lot more power at the rear wheels too!
if you want to get good mileage and decent torque and limit yourself to 1500rpm-3500rpm the small port vortec type heads work great on a 350,thats what G.M. spent the money researching the design to do! ,they are after all TRUCK HEADS!
but increase the displacement to 383 or more and spin the engine to 6500rpm and they become a huge restriction!
while a larger head can give up very little if anything down low in the rpm range but pull far bigger numbers on the hp/tq up higher in the rpm range simply because its still able to flow the necessary voluum of air the engine needs, G.M. knows that! but they also know that 90% plus of the time EMISSIONS and GAS MILEAGE and smooth just off idle low rpm torque is where most engines are used, so they build to fit MOST users expectations

http://www.rbracing-rsr.com/runnertorquecalc.html

play with the calculator,, notice the vortec heads 1.66 are would peak the torque at about 3100rpm on a 383, while a dart 215 cc with its 2.14 port only moves it up to about 3950 rpm AND THATS ASSUMING the larger port head has a matching larger intake runner the whole way to the carb venturies, if you stuck the same intake and other mathing components on BOTH cylinder heads the differance in rpm ranges would be more likely to be in the 300rpm range

EXAMPLE

http://cgi.ebay.com/ebaymotors/ws/eBayISAPI.dll?ViewItem&category=33615&item=7965364790&rd=1

BTW notice the 215cc heads and the strong torque curve????? its fairly obvious from the dyno chart this combo is UNDER CAMMED to make good low rpm tq at the sacrifice of potential top rpm power,

power/tq starts to fall off at about 3700rpm,while thats a good idea in a street engine, you could pick up some mid and top rpm power by swapping to a slightly wilder durration cam PROVIDED THE REST OF YOUR COMBO, like the trans stall speed and rear gear allow it
just some info
a 10.3:1 cpr 383 with 215cc alunminum heads if its matched to a 3000rpm stall converter and 3.73-4.56 rear gears makes a really nice power curve with a cam similar to the CRANE 114681 or lunati voodoo 60104 or for that matter most cams with a 235-245 intake duration and about a .510 or greater lift on a 110-112 LSA
swapping to a cam like that would boost power significantly (40-50hp)_but also make it less street driver friendly in that it would require the drivetrain changes above ans sound like a race engine at idle and would be unlikely to pass emmission testing

"Is there any problems with an under cammed engine? "

no! not if low and mid range torque and NOT peak horsepower is the goal.....but Id like to point out again that the 215cc ports size makes very good low an mid range rpm torque if the compression and cam used are designed for very good low an mid range rpm torque, the comon crap you always hear about port size being very critical to low rpm torque is just that ( mostly CRAP), its just not as important as displacement, compression or cam timing to the results and small cross section ports restrict high rpm power far more than large ports hurt low rpm torque IF THE OTHER COMPONENTS in the combo are DESIGNED to produce mid range tq/power

to answer your question, AND keep anyone reading this up to speed on what we are talking about I think we need to explain a few factors that also need to be looked at. look here
these are the valve timeing overlap ranges that are most likely to work correctly

trucks/good mileage towing 10-35 degs overlap
daily driven low rpm performance 30-55degs overlap
hot street performance 50-75 degs overlap
oval track racing 70-95degs overlap
dragster/comp eliminator engines 90-115 degs overlap
torque is basically the result of cylinder pressure (dynamic compression) and leverage (stroke) plus the NUMBER OF POWER STROKES PER MINUTE (rpm) from the cylinders that are efficiently filled (volumetric efficiency). up to a certain rpm level the cylinders don,t efficiently fill due to low port air speed, above that level the valves and pistons move too fast to effectively fill the cylinders due to lack of time. your highest torque will be at the point where the engine spins the fastest it can while still packing the cylinders to the max efficiency.
here read this info
http://www.babcox.com/editorial/us/us110128.htm

then look at the chart to get a rough idea as to the duration necessary to fill the cylinders effectively . duration , lift and LSA are all a combo that must match compression, displacement, rod length to stroke ratio,port size and length,exhaust scavageing effectiveness, ETC.
look here
http://www.iskycams.com/ART/techinfo/ncrank1.pdf
then look at your cam spec sheet, the piston compresses nothing untill the piston has reached the point where both valves are closed, from that point on your compressing the voluum in the cylinder. look at this cam

http://www.compcams.com/information/search/CamDetails.asp?PartNumber=12-433-8
the pistons not compressing anything untill 77 degrees past BDC, looking at the other chart we see that the piston is about 2.4" down the bore on a 350 chevy not the 3.5 inches that the engines static compression in theory could compress

heres the answer to a similar post that fits here very closely

first is that the port can only flow when the valve is open......and THAT depends on the cam timing and displacement and rod to stroke ratio,.and .050 lift is a good place to judge or compare port flow from so you have some basis to compare from when looking into potential changes.
next, the chevy v8 operates on a 720 degree repetative cycle of which ,if we measure from .050 lift we find ONLY about 200-250 of those 720 degrees are potentially flowing air thru the port or 28% to 35% of the time

PORT SIZE FLOW AND THE RELATION TO CAM DURATION

FIRST, This will not be anything more that a brief glimpse into a subject that takes years to understand fully and IÃ¢â‚¬â„¢m sure there are a few people on the site that can give more exact info! This is meant to apply to the 350-383 sbc engines most of us are useing
My purpose is merely to give an idea as to the relationship between the factors and yes IM ignoring several minor factors to make things easier to understand like dynamic compression and valve timing overlap
But lets look a a few concepts
(1) There are 720 degrees in a 4 cycle engines repetitive cycle of which between about 200degrees to about 250 degrees actually allow air to pass into the cylinder, (the valves open far enough to flow meaningful air flow) and the piston has a maximum ability to draw air into that cylinder based mostly on the engines displacement and the inertia of column of air in both the intake port and the suction (or negative pressure the PROPERLY designed headers provide) this produced a max air flow thru the ports, the greater the volume of fuel/air mix effectively burn per power stroke the greater the engines potential torque production, the faster you spin an engine the greater the NUMBER OF POWER STROKES PER MINUTE, and up to the point where the cylinder filling effectiveness starts falling off due to not enough time available to fill that cylinder the torque increases, above that rpm or peak torque itÃ¢â‚¬â„¢s a race between more power stokes and lower power per stroke
(2) look at this diagram
(3)

As air enters an engine it normally travels thru both an intake system and the cylinder heads intake port to eventually pass into the cylinder thru the valve. The valves in a normal small block corvette engine are between 1.94 and 2.08 in diameter, thatÃ¢â‚¬â„¢s between 2.9sq inches and 3.4 sq inches of area, but because the valves require a seat that at a minimum are about 85%-90% of that flow area we find that the intake port even with out any valve has a max flow of not more than about 90% of the flow thru a port of valve size. Or in this case 2.46 sq inches-2.9 sq inches of port area, Since you gain little if any flow having a port thatÃ¢â‚¬â„¢s substantially larger than the valves AT NORMAL ATMOSPHERIC pressures and since you canÃ¢â‚¬â„¢t substantially increase the valve sizes for several mechanical reasons you must improve efficiency, this is done in two major ways, you can match the intake port length and cross sectional area to the engines most efficient rpm range on the intake side, to build a positive pressure behind the intake valve as it opens and match the exhaust length and diameter on the exhaust side to provide a negative pressure to help draw in more volume this will require the cam timing match that same rpm range of course. By experimentation its been found that air flow port speeds in the 200-320 cubic feet per minute range are about the best for a chevy V-8 now lets say you have a 383. 383/8=47.875 cubic inches per cylinder, the rpm range most used is 1500rpm-6000rpm so thatÃ¢â‚¬â„¢s where are cam and port size must match, you can do the math , (47.875 x Ã‚Â½ engine rpms = cubic inches, divided by your cams effective flow duration, (use 210-235) as a default for a stock cam) x 720 degrees/1728 (the number of cubic inches in a cubic foot) to get the theoretical max port flow required (I will save you the trouble its 250cfm-275cfm at max rpms and about 2.4-2.9 sq inches of port cross section, depending on where you want the torque peak, or use this handy calculator,

Intake Runner Area = Cylinder Volume X Peak Torque RPM 88200
Or this helpful site http://www.babcox.com/editorial/us/us110128.htm

Either way youll find that youll want a port size in the 2.4sq -â€œ2.9 sq inch area
Now use this calculator to figure ideal port length, REMEMBER youll need to add the 6 in the cylinder head to the intake runner length to get the total length and you can,t exceed the engines REDLINE RPM which with hydrolic lifters seldom is higher than 6400rpm
http://www.bgsoflex.com/intakeln.html

Ever wonder why your engines torque curve gets higher with the engines rpm level until about 4000rpm-5500rpm(DEPENDING ON YOUR COMBO) but fades above that rpm level?
well it depends on several factors, first as long as the cylinders can fill completely you get a good fuel/air burn so you get a good cylinder pressure curve against the piston each time the cylinder fires, THE ENGINES TORQUE CURVE INCREASES WITH THE NUMBER OF EFFECTIVE POWER STROKES PER SECOND, at very low speeds theres not enough air velocity to mix the fuel correctly or produce a effective ram tuning effect but as the rpms increase the cylinders fill very efficiently until the rpms reach a point where the cylinders just don,t have the time necessary to flow
enough air through the valves to fill the cylinders , remember a 5000rpm the intake valve out of 720 degs. in each cycle opens for about 250degs of effective flow even with a hot roller cam, now thats only about 35% of the time and theres 41.6 intake strokes per second , thats only 1/60th of a second for air to flow into the cylinder
Its your engines ability to fill the cylinders that increases your power and the more efficiently you do that the higher the rpm level you can accomplish that at the more power your engine makes, remember the formula for hp is (torque x rpm/ 5252=hp) so moving the torque curve higher in the rpm range increases hp but at some point the time available to fill the cylinders becomes so short that efficiency begins to drop off rapidly, the peak of efficiency is reached normally in the 4500rpm-5500rpm range, and as rpms increase its a race between more power strokes per minute trying to raise the power and the increasingly less effective percentage of cylinder filling dropping the power.
Volumetric Efficiency
The volumetric efficiency of a 4-stroke engine is the relationship between the quantity of intake air and the piston displacement. In other words, volumetric efficiency is the ratio between the charge that actually enters the cylinder and the amount that could enter under ideal conditions. Piston displacement is used since it is difficult to measure the amount of charge that would enter the cylinder under ideal conditions. An engine would have 100% volumetric efficiency if, at atmospheric pressure and normal temperature, an amount of air exactly equal to piston displacement could be drawn into the cylinder. This is not possible, except by supercharging, because the passages through which the air must flow offer a resistance, the force pushing the air into the cylinder is only atmospheric, and the air absorbs heat during the process. so, volumetric efficiency is determined by measuring (with an orifice or venturi type meter) the amount of air taken in by the engine, converting the amount to volume, and comparing this volume to the piston displacement.
this increases until the torque peak then falls as the rpms increase. Here is a rough guide to match duration to port flow at different rpm level

if youve been following along youll find that youÃ¢ll need intake ports about 2.3-2.9Ã¢â‚¬Â sq inches in cross section, and between 12Ã¢â‚¬Â and 21 Ã¢â‚¬Å“ long (DEPENDS ON WHERE THE ENGINE IS DESIGNED TO MAKE MAX HP) and cam timing in the 215@.050 to -240@.050 lift range, as the rpms or displacement increase either the port flow or the cams duration must increase or the engines cylinder fill efficiency rpm will drop!
Now this is important, as the port flow efficiency goes up though the use of longer and larger intake ports the cam duration could remain the same or even be lower and you get more efficient cylinder filling as the rpms increase, thatÃ¢â‚¬â„¢s why high efficiency port designs like on the LS1 can use lower duration cams to flow similar total air flow thru the ports than the lower efficiency ports like the old fuelie heads could but at some point all ports reach max flow and an increase in the time the valves remain open at higher rpms increases the cylinder fill efficiency and that increases the engines ability to make torque at that rpm range
if you pick a smaller runner or longer runner you should pick a cam with a shorter duration to match the resulting lower torque peak that will likely result

Id like to point out something here!
EXAMPLE (DYNO SHEET)
LOOK CLOSELY AT THE TORQUE CURVE
heres the combo
SBC 407
Ã‚Â· Block, 509, +30, Zero deck, Blanked water passages, Clearanced oil ways, Lifter valley vents, ARP main & head studs, Durabond cam & Clevite 77 main bearings.
Ã‚Â· Crank, Scat 4340 forged steel, 3.75Ã¢â‚¬Â, internal balance, Pioneer SFI balancer + ARP bolt.
Ã‚Â· Rods, Comp. Products 6.00Ã¢â‚¬Â H beam bronze bushed + ARP bolts Clevite 77 bearings.
Ã‚Â· Pistons, SRP #4032 flat top, 5cc relief, Speed Pro plasma moly file fit rings.
Ã‚Â· Complete rotating assembly balanced. Including - Flywheel, Clutch, Balancer & Crank pulley.
Ã‚Â· Heads, AFR 210 Race Ready, 76cc, 2.080/1.600 valves, drilled for steam. FelPro #1014 gasket.
Ã‚Â· Cam, Comp. Cams Ã¢â‚¬ËœMagnumÃ¢â‚¬â„¢ #12-450-8 (286HR) Hydraulic roller.
230/230 @ .050, .377 lift 110 LSA 106 ICL.
Ã‚Â· Pushrods, Howards Cams heavy wall 5/16Ã¢â‚¬Â 7.4Ã¢â‚¬Â long.
Ã‚Â· Rockers, Pro Magnum roller, 1.6, 7/16Ã¢â‚¬Â stud.
Ã‚Â· Lifters, Pro Magnum hydraulic roller. AFR Hydr-Rev kit.
Ã‚Â· Comp Cams Springs #950 + #740 retainers installed at 1.875Ã¢â‚¬Â
Ã‚Â· AFR rev kit, AFR stud girdle.
Ã‚Â· Lube, Melling M99HVS pump, Canton 7qt 5 trap pan with inbuilt windage and scraper, Cooler, Accumulator, oil stat, remote filter.
Ã‚Â· Holley 800cfm #4780C, 1Ã¢â‚¬Â spacer, Victor Jr single plane.
Ã‚Â· Static CR 10.32, Dynamic CR 7.9.
Ã‚Â· Quench 0.0415Ã¢â‚¬Â (Gasket .039Ã¢â‚¬Â + .0025Ã¢â‚¬Â down hole).
Ã‚Â· MSD Pro Billet Street Dizzy, MSD 6AL, MSD Blaster 2 coil, MSD 8,5mm leads.

Id like to point out something here to those of you who keep insisting that your required to run small ports sizes and dual plane intakes to make decent mid range torque
look closely at what the combo uses

Heads, AFR 210 Race Ready, 76cc, 2.080/1.600 valves, drilled for steam. FelPro #1014 gasket.
Ã‚Â· Cam, Comp. Cams Magnum #12-450-8 (286HR) Hydraulic roller.
230/230 @ .050, .377 lift 110 LSA 106 ICL.
Holley 800cfm #4780C, 1" spacer, Victor Jr single plane

like IVE CONSTANTLY SAID, ITS THE CAM AND PROPERLY MATCHED COMPRESSION RATIO THAT HAS THE LARGEST EFFECT ON THE ENGINES TORQUE POTENTIAL, while its true that smaller ports can increase the volumetric efficiency at low rpms, they are not always required, and the tend to hurt the high rpm performance, you also don,t need a great deal of duration in the cam you pick,if the heads your useing flow decently, notice hes only running 230 @.050 lift
LARGE ports matched to the correct compression ratio and cam can make very good torque.
as always its the total combo OF PARTS and how the parts match the displacement and intended rpm range, NOT the result of a SINGLE PART choice!

grumpyvette · Oct 20, 2008

PORT SIZE FLOW AND THE RELATION TO CAM DURATION

FIRST, This will not be anything more that a brief glimpse into a subject that takes years to understand and Im sure there are a few people on the site that can give more exact info! This is meant to apply to the 350-383 sbc engines most of us are using
My purpose is merely to give an idea as to the relationship between the factors and yes IM ignoring several minor factors to make things easier to understand
But lets look a a few concepts
(1) There are 720 degrees in a 4 cycle engines repetitive cycle of which between about 200degrees to about 250 degrees actually allow air to pass into the cylinder, (the valves open far enough to flow meaningful air flow) and the piston has a maximum ability to draw air into that cylinder based mostly on the engines displacement and the inertia of column of air in both the intake port and the suction (or negative pressure the PROPERLY designed headers provide) this produced a max air flow thru the ports, the greater the volume of fuel/air mix effectively burn per power stroke the greater the engines potential torque production, the faster you spin an engine the greater the NUMBER OF POWER STROKES PER MINUTE, and up to the point where the cylinder filling effectiveness starts falling off due to not enough time available to fill that cylinder the torque increases, above that rpm or peak torque itÃ¢â‚¬â„¢s a race between more power stokes and lower power per stroke
(2) look at this diagram

a very common misconception, "that the intake runner size has the most effect on the engines torque curve,is mostly a myth" in reality ,compression ratio, cam timing and engine displacement and proper exhaust scavenging ALL have a larger effect on the engines torque that the intake runner cross sectional area.(yes getting it correct helps but your more likely to cause a problem by selecting an intake port and runner combo thats too small and restrictive than one thats too large in cross sectional area.

torque curve closely matches the cylinder fill efficiency ,
(3)
As air enters an engine it normally travels thru both an intake system and the cylinder heads intake port to eventually pass into the cylinder thru the valve. The valves in a normal small block corvette engine are between 1.94 and 2.08 in diameter, thats between 2.9sq inches and 3.4 sq inches of area, but because the valves require a seat that at a minimum are about 85%-90% of that flow area we find that the intake port even with out any valve has a max flow of not more than about 90% of the flow thru a port of valve size. Or in this case 2.46 sq inches-2.9 sq inches of port area, Since you gain little if any flow having a port thats substantially larger than the valves AT NORMAL ATMOSPHERIC pressures and since you can not substantially increase the valve sizes for several mechanical reasons you must improve efficiency, this is done in two major ways, you can match the intake port length and cross sectional area to the engines most efficient rpm range on the intake side, to build a positive pressure behind the intake valve as it opens and match the exhaust length and diameter on the exhaust side to provide a negative pressure to help draw in more volume this will require the cam timing match that same rpm range of course. By experimentation its been found that air flow port speeds in the 200-320 cubic feet per minute range are about the best for a chevy V-8 now lets say you have a 383. 383/8=47.875 cubic inches per cylinder, the rpm range most used is 1500rpm-6000rpm so thats where are cam and port size must match, you can do the math , (47.875 x Ã‚Â½ engine rpms = cubic inches, divided by your cams effective flow duration, (use 210-235) as a default for a stock cam) x 720 degrees/1728 (the number of cubic inches in a cubic foot) to get the theoretical max port flow required (I will save you the trouble its 250cfm-275cfm at max rpms and about 2.4-2.9 sq inches of port cross section, depending on where you want the torque peak, or use this handy calculator,

Intake Runner Area = Cylinder Volume X Peak Torque RPM 88200
Or this helpful site
http://www.rbracing-rsr.com/runnertorquecalc.html
before you reach for your wallet, do some basic math and read a few dozen related links
http://www.wallaceracing.com/calcafhp.php

http://www.superchevy.com/how-to/en...-0902-chevy-engine-port-variations-measuring/

http://www.gmhpclub.com/performancecalculators.htm

http://garage.grumpysperformance.com/index.php?threads/port-speeds-and-area.333/#post-37705
USE THE CALCULATORS to match port size to intended rpm levels... but keep in mind valve lift and port flow limitations
http://www.wallaceracing.com/runnertorquecalc.php
http://www.wallaceracing.com/ca-calc.php
http://www.wallaceracing.com/area-under-curve.php
http://www.wallaceracing.com/chokepoint.php
http://www.wallaceracing.com/header_length.php
http://www.circletrack.com/enginetech/1 ... ch_engine/

http://www.wallaceracing.com/calcafhp.php

http://hpwizard.com/engine-horsepower-calculator.html

http://www.hotrod.com/articles/airflow-research-cylinder-power/

http://www.powerperformancenews.com/tech-articles/cylinder-head-tech-airflow-vs-power/

http://www.calculator.net/engine-horsepower-calculator.html

http://www.calculatoredge.com/new/horsepower.htm

Either way youÃ¢â‚¬â„¢ll find that youÃ¢â‚¬â„¢ll want a port size in the 2.4sq Ã¢â‚¬â€œ2.9 sq inch area
Now use this calculator to figure ideal port length, REMEMBER youll need to add the 6Ã¢â‚¬Â in the cylinder head to the intake runner length to get the total length and you can,t exceed the engines REDLINE RPM which with hydrolic lifters seldom is higher than 6400rpm

http://www.bgsoflex.com/intakeln.html

http://garage.grumpysperformance.co...video-with-info-worth-watching-through.15999/
Ever wonder why your engines torque curve gets higher with the engines rpm level until about 4000rpm-5500rpm(DEPENDING ON YOUR COMBO) but fades above that rpm level?
well it depends on several factors, first as long as the cylinders can fill completely you get a good fuel/air burn so you get a good cylinder pressure curve against the piston each time the cylinder fires, THE ENGINES TORQUE CURVE INCREASES WITH THE NUMBER OF EFFECTIVE POWER STROKES PER SECOND, at very low speeds theres not enough air velocity to mix the fuel correctly or produce a effective ram tuning effect but as the rpms increase the cylinders fill very efficiently until the rpms reach a point where the cylinders just dont have the time necessary to flow
enough air through the valves to fill the cylinders , remember a 5000rpm the intake valve out of 720 degs. in each cycle opens for about 250degs of effective flow even with a hot roller cam, now thats only about 35% of the time and theres 41.6 intake strokes per second , thats only 1/60th of a second for air to flow into the cylinder
Its your engines ability to fill the cylinders that increases your power and the more efficiently you do that the higher the rpm level you can accomplish that at the more power your engine makes, remember the formula for hp is (torque x rpm/ 5252=hp) so moving the torque curve higher in the rpm range increases hp but at some point the time available to fill the cylinders becomes so short that efficiency begins to drop off rapidly, the peak of efficiency is reached normally in the 4500rpm-5500rpm range, and as rpms increase its a race between more power strokes per minute trying to raise the power and the increasingly less effective percentage of cylinder filling dropping the power.
Volumetric Efficiency
The volumetric efficiency of a 4-stroke engine is the relationship between the quantity of intake air and the piston displacement. In other words, volumetric efficiency is the ratio between the charge that actually enters the cylinder and the amount that could enter under ideal conditions. Piston displacement is used since it is difficult to measure the amount of charge that would enter the cylinder under ideal conditions. An engine would have 100% volumetric efficiency if, at atmospheric pressure and normal temperature, an amount of air exactly equal to piston displacement could be drawn into the cylinder. This is not possible, except by supercharging, because the passages through which the air must flow offer a resistance, the force pushing the air into the cylinder is only atmospheric, and the air absorbs heat during the process. so, volumetric efficiency is determined by measuring (with an orifice or venturi type meter) the amount of air taken in by the engine, converting the amount to volume, and comparing this volume to the piston displacement.
this increases until the torque peak then falls as the rpms increase. Here is a rough guide to match duration to port flow at different rpm level

if youve been following along youll find that youll need intake ports about 2.3-2.9Ã¢â‚¬Â sq inches in cross section, and between 12Ã¢â‚¬Â and 21 Ã¢â‚¬Å“ long (DEPENDS ON WHERE THE ENGINE IS DESIGNED TO MAKE MAX HP) and cam timing in the 215@.050 to -240@.050 lift range, as the rpms or displacement increase either the port flow or the cams duration must increase or the engines cylinder fill efficiency rpm will drop!
Now this is important, as the port flow efficiency goes up though the use of longer and larger intake ports the cam duration could remain the same or even be lower and you get more efficient cylinder filling as the rpms increase, thats why high efficiency port designs like on the LS1 can use lower duration cams to flow similar total air flow thru the ports than the lower efficiency ports like the old fuelie heads could but at some point all ports reach max flow and an increase in the time the valves remain open at higher rpms increases the cylinder fill efficiency and that increases the engines ability to make torque at that rpm range

grumpyvette · Nov 21, 2008

I CAN,T EVEN TELL YOU HOW INSANE SOME CONVERSATIONS ARE! GUYS TELL YOU A 210CC AFR (AIR FLOW RESEARCH) HEADS GOING TO KILL TORQUE ON A 383 BUT ITS FINE FOR A 400 SBC, WHAT B.S.,,
the same guys that tell you you should have used 195cc heads on your 383,sbc will all point to the larger 210cc head as having lower port flow speeds, while that's true, the amount of the port flow reduction is all but meaningless, AT ANY RPM POINT, if you ask them how much the port flow was reduced you'll never get a firm intelligent answer because they don,t have a clue, and are just repeating , like mindless parrots,crap they heard. DO YOU REALLY THINK SUBTRACTING 4% FROM THE DISPLACEMENT OR ADDING 1% TO THE PORTS CROSS SECTIONAL AREA WILL HURT THE TORQUE NEARLY AS MUCH AS THE ADDED PORT FLOW HELPS THE UPPER RPM POWER CURVE
the difference is about 1%
the 210cc heads superior,REMEMBER ITS NOT THE HEADS PORT VOLUME BUT THE COMPLETE RUNNER LENGTH AND CROSS SECTION, PLUS THE PLENUM VOLUME, THAT WILL EFFECT PORT FLOW SPEEDS, FLOW SPEEDS WILL BE EQUAL OR HIGHER JUST 100-200RPM HIGHER IN THE POWER CURVE WITH THAT 383 VS A 400SBC...... and your correct! the cam, intake and other factors far out weight the difference in port cross section and flow speed differences, any reduction in torque is due to lower compression, a different cam or the intake or header design not the port size difference, and the 210cc head has a marked advantage with the larger cams
JUST REMEMBER THE 210CC HEADS ARE DESIGNED FOR sbc combos WITH CAMS WITH OVER .575 LIFT AND OVER 245 DEGS DURATION AT .050 LIFT, AND COMPRESSION RATIOS OVER 10.5:1 IF YOUR LOOKING TO GET THE FULL ADVANTAGE FROM THE PORT DESIGN, AND DISPLACEMENTS OF 377 PLUS
here
http://www.airflowresearch.com/super-chevy-apr-2010-210cc-sbc.php

http://www.rbracing-rsr.com/runnertorquecalc.html

http://www.compcams.com/Community/Articles/Details.asp?ID=1737510521

http://users.erols.com/srweiss/tablehdc.htm

viewtopic.php?f=52&t=1751&p=4387#p4387

http://www.malcams.com/legacy/misc/headflow.htm

http://victorylibrary.com/mopar/intake-tech-c.htm

ok first point lets go thru some basics, on port flow restriction,AND AT FIRST LETS DISCUSS STOCK OR NEARLY STOCK SBC PORTS AND HEADS, the typical intake gasket might look like your dealing with a 1.2" x 2" tall port or a 2.4 sq inch opening but in reality its generally slightly smaller at the narrow point in the port, where the push rods restrict the port size.
the port cross sectional area at the narrowest point will be the restriction, that choke point in the runner not the valve size in most applications, is the weak link, WHY?
just like a chains only as strong as its weakest link, a port will only flow up to its tightest restriction,
well your 2.02 valve has a circumference of just over 6" so at about .400 lift the valves curtain area exceeds the throat restriction cross section, in your typical sbc heads , but remember the port throat rarely exceeds 90% of the valve diam.(there's obviously an area for the valve to seal/seat against) so the true opening under a 2.02" valve will rarely be larger than a 1.8" circle or about a 2.6sq inch area, reduced further by the valve stem,your looking at about 2.3 sq inches in a factory head or the smaller port aftermarket sbc heads.
remember the valve lifts off its seat,reaches peak lift, then returns to its seat, so its at peak lift once but passed thru the lower lift flow rates, twice making those flow rates far more important to total flow, measured, thru the port.

heres a chart FROM THE BOOK,HOW TO BUILD BIG-INCH CHEVY SMALL BLOCKS with some comon cross sectional port sizes
(measured at the smallest part of the ports)
...........................sq inches........port cc
edelbrock performer rpm ....1.43.............170
vortec......................1.66.............170
tfs195......................1.93.............195
afr 180.....................1.93.............180
afr 195.....................1.98.............195
afr 210.....................2.05.............210
dart pro 200................2.06.............200
dart pro 215................2.14.............215
brodix track 1 .............2.30.............221
dart pro 1 230..............2.40.............230
edelbrock 23 high port .....2.53.............238
edelbrock 18 deg............2.71.............266
tfs 18 deg..................2.80.............250

AFR 195 Eliminators
actual cc's in the intake port.....184
cross section area...2.13 sq.in
Flow spec's.....281/221

AFR 195 comp Eliminators
actual cc's ....189
cross section...2.15 sq.in
Flow spec's...306/235

Trick Flow 195 K D
before porting actual cc's....185
after porting ...188
cross section....2.13 sq.in
Flow spec's....270/210

Edelbrock Etec 200's
actual cc's before porting N/A
after porting....197
cross section...2.13
Flow spec's...270/218

(flow spec's @ .600 lift)

now that means that as long as the valve remains over about .400 lift the port flow is going to be close to maximum levels, yes IM fully aware every flow chart you see shows port flow increases on typical SBC heads up to about .500-.550 of lift, but in the real world its the flow below .500 lift that maters and in most street cars the cams don,t exceed about .550-.570 peak lift, lets look at time, at peak hp your probably running at between 6000rpm-7000rpm with most combos, there's a 720 degree cycle the engine goes thru and only about 45 degrees are at peak lift, 45 degrees out of that 720 degree repetitive cycle, or about 1/8th of the intake stroke while the valve might be at the lower lifts up to about 180 degrees, or as much as 4 times as long.

Potential HP based on Airflow (Hot Rod, Jun '99, p74):
Airflow at 28" of water x 0.257 x number of cylinders = potential HP
or required airflow based on HP:
HP / 0.257 / cylinders = required airflow

ITS A COMMON MISCONCEPTION,THAT YOU MEASURE PORT CROSS SECTION AT THE PORT ENTRANCE,BUT ITS NOT the port area at the entrance , you need to use in the calculations, ITS the MINIMAL port cross section at the SMALLEST point in the port, usually near the pushrod area.
LIKE a funnel, its not the largest part of the opening but the smallest that's the restriction to flow, so invest a couple dollars in snap gauges and a dial caliper, youll be amazed at what you learn, about ports and flow

http://www.wallaceracing.com/chokepoint.php

http://www.wallaceracing.com/chokepoint-rpm.php

http://www.wallaceracing.com/dynamic-cr.php

http://www.kb-silvolite.com/calc.php?action=comp2

http://www.wallaceracing.com/lpv.php

http://www.wallaceracing.com/dynamic-cr.php

SO HOW do you MEASURE THEN??

http://www.harborfreight.com/cpi/ctaf/displayitem.taf?Itemnumber=5649

http://store.summitracing.com/partdetail.asp?autofilter=1&part=SUM-900014&N=700+115&autoview=sku

runner LENGTH and CROSS SECTION plus PLENUM VOLUME (if there is a plenum)effects the intake harmonics and how effectively you can ram tune the intake runner charge to fill the cylinders, and don,t forget exhaust scavaging , compression ratio and cam timing, and valve curtain area,and drive train gearing must match the intended combos effective operational power band

http://victorylibrary.com/mopar/intake-tech.htm

http://www.rbracing-rsr.com/runnertorquecalc.html

http://www.bgsoflex.com/intakeln.html

http://www.engr.colostate.edu/~allan/fluids/page7/PipeLength/pipe.html

IF you take this advice seriously youll save ALOT of time and money

DO YOURSELF A HUGE FAVOR
buy these books, FIRST it will be the best money you ever spent, read them, and you will be miles ahead of the average guy. youll save thousands of dollars and thousands of hours once you've got a good basic understanding of what your trying to do!

http://www.themotorbookstore.com/resmchstvi.html

how to assemble an engine basics on video

these books

HOW TO BUILD MAX PERFORMANCE CHEVY SMALL BLOCKS ON A BUDGET by DAVID VIZARD
http://www.amazon.com/Build-Perform...=sr_1_1?ie=UTF8&s=books&qid=1195231793&sr=1-1

JOHN LINGENFELTER on modifying small-block chevy engines

http://www.amazon.com/John-Lingenfe...=sr_1_1?ie=UTF8&s=books&qid=1195231760&sr=1-1

SMOKEY YUNICK,S POWER SECRETS

http://www.amazon.com/Smokey-Yunick...=sr_1_1?ie=UTF8&s=books&qid=1195231724&sr=1-1

How to Rebuild Small-Block Chevy Lt1/Lt4 Engines
http://www.amazon.com/Rebuild-Small-Block-Chevy-Engines-Hp1393/dp/1557883939/ref=pd_sim_b

grumpyvette · Dec 2, 2008

keep in mind swapping heads gives you the option to increase or decrease the compression ratio of the combo, and once the compression ratios increased you can use a longer duration cam timing without sacrificing a great deal of low rpm torque, that you would loose with the lower compression ratio if the same cam were installed in the lower cpr combo

assume on a stock 350 small block)

Speaking in generalities and assuming no other changes, what's the relation between cylinder head combustion chamber size and overall engine compression?

Does just changing heads from a stock 76cc head, to a head with a smaller chamber make that much overall difference on engine c/ratio? Such as a 64cc or 58cc chamber. How about changes on necessary octane requirement?

Just curious to see what can be expected. I've read plenty on what performance gains can be had and what would work best for 350 TPI, but curious to see the other factors may play out.

Thanks"
Ok lets look at it a bit, theres two types of compression ratio, static and dynamic, keep in mind its MOSTLY dynamic compression ratio, that effects your results.
youll gain about 3% in hp increasing the effective static compression ratio one full point, so swapping from a 9:1 to a 10:1 cpr boost torque about 3%
swapping from a 76cc head to a 58cc head is a 1.84:1 cpr change so you can reasonably expect a 1.84 x 3% or a 5.52% boost in torque from that change alone.
if your current engine made 330hp that would jump to about 5.52% higher if the tq curve remained consistant, so youll see about 350 hp.

one of the the main functions of compression is to pack the fuel/air mix into a tight area for both fast effective ignition and to provide a mechanical advantage for the piston & rod assembly to push against the crank throw,as that mass in the combustion chamber burns and rapidly expands.

lets look ast your question, given identical 350 displacement engines with flat top pistons and a common .032 thick head gasket, a .023 deck and 5cc valve notches, heres what your going to see in STATIC COMPRESSION,as a result of combustion chamber changes

58cc=10.61/1
60cc=10.36/1
62cc=10.12/1
64cc=9.89/1
68cc=9.47/1
72cc=9.09/1
74cc=8.91/1
76cc=8.75/1

keep in mind you want to stay at about 8:1-8.5:1 in DYNAMIC compression

to run comon pump gas without getting into detonation
that depends on the fuel octane, cylinder head temp. and several other variables but generally 8.0-8.5:1 dynamic works out well if your going to run mid grade pump gas

lets do a bit of math
just a bit of info on intake gaskets sizes to match port cross sectional areas

Calculating the valve curtain area
The following equation mathematically defines the available flow area for any given valve diameter and lift value:
Area = valve diameter x 0.98 x 3.14 x valve lift
Where 3.14 = pi (π)
For a typical 2.02-inch intake valve at .500-inch lift, it calculates as follows:
Area = 2.02 x 0.98 x 3.14 x 0.500 = 3.107 square inches
SO lets do a bit of math
a cylinder head with a 2.02' intake valve and a cam with a .450 lift at the valve with a 1.5:1 rocker will in theory produce a valve curtain area of 2.79 sq inches, swapping to a 1.6:1 ratio increases the lift to .480 lift 2.98 sq inches, increasing the available port flow potential at least in theory by about 6%, but keep in mind the port can only flow at full valve lift for the limited time the valve remains at full lift and if the narrowest section of the port cross sectional areas less that the valve curtain area that not the valve restricts flow
THUS the most you can reasonably expect is a 6% flow increase , from the rocker ratio upgrade but reality and the fact that the valve is opening and closing perhaps 57 times a second at peak rpms, and the port may be more restrictive that the valve curtain area, on many small block combos suggests the results will be lower

viewtopic.php?f=52&t=148&p=34936&hilit=calculate+port+stall#p34936

heres a chart FROM THE BOOK,HOW TO BUILD BIG-INCH CHEVY SMALL BLOCKS with some common cross sectional port sizes
(measured at the smallest part of the ports)
...........................sq inches........port cc
edelbrock performer rpm ....1.43.............170
vortec......................1.66.............170
tfs195......................1.93.............195
afr 180.....................1.93.............180
afr 195.....................1.98.............195
afr 210.....................2.05.............210
dart pro 200................2.06.............200
dart pro 215................2.14.............215
brodix track 1 .............2.30.............221
dart pro 1 230..............2.40.............230
edelbrock 23 high port .....2.53.............238
edelbrock 18 deg............2.71.............266
tfs 18 deg..................2.80.............250

USE THE CALCULATORS
http://www.rbracing-rsr.com/runnertorquecalc.html
http://www.wallaceracing.com/chokepoint.php
http://www.wallaceracing.com/header_length.php

COMMON SBC INTAKE PORTS
felpro # 1204=Port Size: 1.23" x 1.99"=2.448 sq inches

felpro # 1205=Port Size: 1.28" x 2.09"=2.67 sq inches

felpro # 1206=Port Size: 1.34" x 2.21"=2.96 sq inches

felpro # 1207=Port Size: 1.38" x 2.28"=3.146 sq inches

felpro # 1209=Port Size: 1.38" x 2.38"=3.28 sq inches

felpro # 1255 VORTEC=Port Size: 1.08" x 2.16"-2.33 sq inches

felpro # 1263=Port Size: 1.31" x 2.02"=2.65 sq inches

felpro # 1266=Port Size: 1.34" x 2.21"=2.96 sq inches

felpro # 1284 LT1=Port Size: 1.25 x 2.04''=2.55 sq inches

felpro # 1289 FASTBURN=Port Size: 1.30" x 2.31" 3.00 sq inches

the valve curtain area, cam duration and lift controlling that curtain area,or port cross sectional area will pose a restriction to air flow at some point,in the engines rpm band, but you can extend the effective air flow duration and efficiency with carefully timed exhaust scavenging, that helps draw in the intake runner inertia load of air/fuel,charge much more effectively if the peak negative pressure wave is correctly timed

calculators

http://kb-silvolite.com/calc.php?action=comp

http://www.csgnetwork.com/compcalc.html

http://www.bgsoflex.com/cr.html

threads/info

http://victorylibrary.com/mopar/chamber-tech-c.htm

http://victorylibrary.com/mopar/piston_position-c.htm

http://victorylibrary.com/mopar/cam-tech-c.htm

http://forum.grumpysperformance.com/viewtopic.php?f=52&t=727

http://forum.grumpysperformance.com/viewtopic.php?f=50&t=499

READ THRU THESE

http://www.gofastnews.com/board/technic ... lumes.html

http://www.gofastnews.com/board/technic ... areas.html

viewtopic.php?f=52&t=796

viewtopic.php?f=52&t=534

viewtopic.php?f=52&t=389

viewtopic.php?f=52&t=333

having the plenum divider fully in place below the carb base, tends to help lower rpm torque and crisp responsiveness to minor throttle position changes, removing the divider effectively increases the plenum volume the runners draw from and that tends to slow low rpm response to throttle changes but it tends of increase the flow rates slightly at high rpms so power in the upper rpm band tends to go up as the plenum volume is less of a restriction.
notching the divider tends to split the difference to some extent.
theres two basic carb spacer designs, they are commonly 1" or 2" tall, the one hole open spacer and the 4 hole designs, the 4 hole design in effect maintains the divided plenum, but adds plenum volume and reduces the restriction the limited space between the carbs venturies and individual intake runner entrances can have in some intake designs.
the open common plenum spacers are designed for use with single plane intakes where adding plenum volume helps upper rpm flow..
naturally you can mix/match and gain or loose plenum volume, and increase the distance from the carb base to the intake runners entrance, which can be helpful, especially if your installing a nitrous plate under the carb, or if your intake currently lacks plenum volume for your application.
as a general guide,and assuming your static compression ratio matches the cam duration you select, if your running less than about a 235 dur @ .050 lift cam, with a 2.57:1-3.36:1rear gear ratio, a dual plane intake should prove beneficial, have more than about 245 degrees dur. @ .050 lift, and a 3.45:1-plus rear gear and a single plane intake will generally prove useful.

you might find this of interest

http://victorylibrary.com/mopar/intake-tech.htm

http://www.circletrack.com/enginetech/c ... index.html

grumpyvette · Oct 20, 2010

Drag Racing Cylinder Head Selection

By Brendan Baker

Brendan Baker

"When you talk about performance heads for drag racing - or any other performance application for that matter - the best heads aren't necessarily the ones with the biggest cubic feet per minute (CFM) numbers. Experts say that the key ingredient is high velocity matched with good flow. But the high flow numbers may blind your customers from seeing the whole picture, so it is up to you to explain.

Some cylinder head experts compare flow numbers to horsepower numbers on a dyno - but guess what? They're not all equal. So if you see one head with extremely high CFM numbers there are a couple of guesses what may be going on. One cylinder head expert says that the general enthusiast/racer doesn't know if the numbers are bogus, all he sees is a big number and that's what he wants.

Larger engines need larger volume ports. And today there are many aftermarket cylinder heads to choose from with larger ports. But before these heads were available, drag racers didn't have many options as to what size heads to use. Most racers would look for the biggest stock head available and adapt it to their application. Yet one of the biggest problems with using stock heads is that you're stuck with the port locations and the thickness of the casting, so you can't get too radical.

Some aftermarket heads have features such as raised runners and relocated ports to improve airflow. Today's aftermarket "as cast" cylinder heads with unmachined ports often flow better than stock heads that have been ported. And "bare" aftermarket heads are available to allow CNC porting to create almost any shape port you want.

Cylinder head specialist Darin Morgan says that with all the aftermarket heads available choosing a cylinder head today is a difficult task. Unfortunately, a bad choice can cost thousands of dollars in wasted time, says Morgan, and a bad head choice may go unnoticed without ever showcasing how good your engine could have been.

So with all the heads on the market, how do you make the right choice? Morgan says it's a complex issue with no simple answer.

"I wish I could lay out some quick and easy mathematical equations or some simple guidelines to help, but there simply aren't any," says Morgan. "It's a complex issue, which is why so many people have trouble. The best way to grasp what's most important is to use what I consider the five most important variables used to tune the induction system:

1.
Average velocity;

2.
Individual instantaneous velocities;

3.
Shape/design (maximize a homogeneous velocity profile over the entire port and at the same time promote efficient flow);

4.
Rate of velocity change; and

5.
Airflow.

Morgan says that if you follow his five variables you'll soon find the most important rules of designing an induction system are: Velocity, Velocity, Shape, Velocity and, finally, Airflow.

We then talked to Curtis Boggs at Race Flow Development (RFD), who says his company takes a bare casting and comes up with its own port designs. He says the design being made determines which head casting will end up being used. "It could be a Dart, Edelbrock or something else - each casting has its own design issues," he says.

Boggs says that most of his customers are professional engine builders who call him to make custom cylinder heads. "Customers who call me tend to call three different shops on a regular basis - we all do high end head work. I can tell who they've called by the CFM number they quote," jokes Boggs. "If it's 20 CFM higher than the laws of physics, then I know who they've talked to."

Boggs reiterates what other cylinder head specialists have said about comparing flow numbers to a dyno rating. "It's become a popular way to sell cylinder heads," says Boggs. "Publications have promoted the CFM number too, probably from a little ignorance (we plead the fifth! - Ed). "While it makes sense that a larger CFM number indicates more air flow, and therefore more power, that's partially true, but it's not the most important aspect in selecting a good cylinder head."

Boggs describes how he designs a cylinder head for an application: "Darin Morgan is a friend of mine and we tend to have a similar philosophy on head design. I tend to be a little more generous on valve size than he is, and I also use the percentage of a bore size as criteria for choosing an intake valve. That is also tied to the size of the throat under the valve, which, as far as I'm concerned, is the most critical dimension. That sets the air speed at which the air exits the valve into the chamber.

"It's all air speed," says Boggs. "If you understand basic fluid dynamics (how things flow and what kind of shapes they like), you'll have well-shaped ports. And if you've designed your port to hit the proper target air speed (it's going to give you a certain size port to hit that speed if you design around the cross-sectional areas), in general, the CFM number should follow that.

"But the CFM number is the last thing I pay attention to," continues Boggs. "If everything else has lined up properly in designing the port, the CFM number should be there. But it's not the number you design around."

So if someone claims 20 more CFM, it's not a good thing? Not necessarily, according to cylinder head experts.

A very good example would be a 500 cid NHRA Pro Stock engine, explains Boggs. He says you can make that cylinder head flow 600 CFM, but for the most part, the front running engines don't typically flow that much.

"I know of one set of Pro Stock heads that won a race and were top qualifier at several other races last year that flowed only 560 CFM peak. That's 40 CFM less than what other people claim their heads produce."

So, explain the experts, while you can technically have the same air speed you may not get the same CFM number.

"That is more common than most people realize," says Boggs. "Many Comp Eliminator style heads have 2.5 or 2.6 hp per cubic inch, or even more, and are very efficient engine combinations. But most people would be surprised at the CFM number for these engines. An example would be the current trend for 300-inch motors with SB2 heads in Comp Eliminator. That particular cylinder head only flows 360 CFM. And at that number most people would want to throw that head in the trash, but it's a record-holding car." In general, you set air speed in a couple of different places in the cylinder head. The simplest example would the 18-degree SBC. Generally, the smallest part of the intake port through the entire tract will be at the pushrod pinch. That's why everyone keeps using offset rockers, trying to make the port bigger. The peak airspeed is from the manifold plenum to the back of the valve.

In addition, the throat behind the valve is the second place you can set airspeed. At the pushrod you have a choke point called the primary choke, so that's the fastest part. And that's the first part when the air goes too fast that it'll choke. So you set your air speed at the pushrod and your exit air speed into the chamber at the throat.

Once you know the bore and stroke of an engine, you have a hole with a piston going up and down, you have to fill it with air. So you know what the volume of air you have to move. Now you can calculate back up to the intake tract and figure you have a certain amount of time to move a specified amount of air, so the port has to be, for instance, 3.2 sq.in of area to move that amount of air at 300 ft. per second.

Boggs says you make adjustments in .100" increments of the cross-sectional area, which are small adjustments. If you adjust .100" you could be affecting the air speed by 20 or 30 ft. per second. They're very precise adjustments.

Boggs and other cylinder head experts say they need to get as much detail as possible from a customer before they can properly design the port. Everything comes under consideration at that point. If it's a road racecar, for example, you have to consider what track it is. If it's a drag race engine it's a little easier because you only have straight-line acceleration.

Subsequently, with drag racing you're solely worried about acceleration rate say experts. In drag racing applications you can get away with a bigger cylinder head and use more gear, a big converter and so on. But there's always a balance. If you make it too big, the car won't ET well. A bigger head will give you more top end power but you can't launch as well.

Here's where guys buying cylinder heads from CFM numbers alone get into trouble, says Boggs. If the cylinder head really does have a bigger number, and it's designed by someone with an uncalibrated flow bench, there's only one way to do that: The hole has to be bigger! You just can't change physics.

"So people who are buying the biggest number they can find also have the biggest holes, and the biggest holes aren't the ones going down the race track the fastest," explains Boggs. "You make most of your ET in a drag race car in the first 60 to 100 feet. You've got to get the car going - that's where the best ET is. Top speed doesn't mean anything. You're not accelerating at the top of the track. If you buy a head based on CFM and the air speed is too slow because of the big hole, the car won't accelerate."

Matt Driskell, Driskell Enterprises, says he looks at how heavy the car is and what's going to be done with it. "On anything up to a 555 cid to 565 cid engine, I'll use a head that's anywhere from 350-360 cc intake runner volume," says Driskell. "If there's an application where the car is a lot heavier, I might use a 320 or 330 cc range, if it needs a lot of torque and doesn't need to peak really high in engine rpm."

Driskell says most of what he's learned about cylinder head work is from his experience at the track and in talking to other experts. "From what I've found, you can look at flow numbers all day long in this range (320-360 cc). But it's just something to look at, in my opinion. You can dry flow the heads all day long and pick the best one but it'll perform differently out on the track."

If you have a Top Dragster that weighs 1,800 lbs. and you're trying to go 8.20 to qualify for your Quick 8 Class at your local track, experts say you'd better pay attention to what you're doing. And that's where you need a cylinder head built for the application.

Street-Strip guys can buy an as cast aftermarket head and put a valve job in it and go. Nothing really comes out of the box ready to go, which is where engine builders come in. A custom head that is built for a specific drag race application will require a lot more work and effort than a mass produced head that you clean up and ship out.

The criteria changes for what you need to do the higher up you go on the drag racing scale. At the mid-level to high-end drag racing classes, air speed is the real key to pay attention to. Remember: a CFM number is a just a number that someone decided to advertise. "

grumpyvette · Dec 3, 2010

Intake and Exhaust Size - Enginology
Sizing Does Matter
From the January, 2011 issue of Circle Track
By Jim McFarland

Inlet And Exhaust Path Sizing
This month, we'll step out of the "theoretical box" and into one that's a bit more practical by discussing and focusing on some fundamental ways of relating inlet and exhaust path sizing to an engine's ability to produce torque. In the process, it's important to understand that what follows can be used as a diagnostic approach to determining why torque boosts occurred where they did, as well as a tool for helping shape a given torque curve to match where an engine needs to perform best.

We'll lace all this with a few examples, just to reinforce the points shared. Also, keep in mind that the approach we'll take is pursued somewhat at the risk of oversimplification because there are far more precise and encompassing methods available. What follows are the type of tools that work well in the dyno room or for basic parts selection, void of any intricate math or computer programs.

We've previously mentioned that both intake and exhaust flow is unsteady and somewhat pulsating, punctuated by interruptions that include the opening and closing of valves and pressure excursions involving the combustion space.

The study of wave motion plays into this, among other analyses. But for purposes of our discussion, let's say there will be a "mean flow velocity" in intake and exhaust paths that occur at or very near peak volumetric efficiency (a torque peak) in both these paths. A commonly-accepted value for this is 240 feet/second. Although many intake manifolds have runners with taper (or slightly varying cross section areas) and some headers incorporate "steps" or sudden changes in flow path cross section, we'll initially assume constant flow path areas and then examine the non-constant areas later in our discussion.

Suppose we begin by evaluating how what we've called "mean flow velocity" plays into intake manifold function. Reliable information has shown an engine's torque peak is directly linked to a mean flow velocity of 240 feet/second. Since flow path section area, engine speed, and piston displacement dictate where in the rpm range this flow rate is reached, there is a mathematical relationship from which any one of these can be determined, if the other values are known or assumed. In a simplified format, the equation is as follows:

Peak Torque rpm = (Flow path area) x (88,200) / Displacement of one cylinder)

As an example case, let's assume a total V-8 engine piston displacement of 350 ci, giving us 43.75 ci/cylinder. If the section area of the intake runner is 3.0 square inches, we can plug these values into our little equation to calculate a corresponding torque peak at 6,048 rpm. At least this is where it should occur. Of course, this only addresses how the intake manifold will contribute to the engine's overall torque curve. If we observe this boost (from the intake manifold) occurring at a lower rpm, we could say the engine is "under-cammed," and if it appears at a higher rpm, the engine could be over-cammed.

So, one use for our equation is to evaluate how a particular intake manifold will influence overall torque, particularly at its mean flow velocity. If we'd like to select/design/modify an intake manifold's runner section area to boost torque at a desired point, the equation can be algebraically rearranged to solve for the required section area to read as follows.

Flow path area = (Peak torque rpm) x (Displacement of one cylinder) / 88,200

In this case, let's assume we'd like an intake manifold torque boost at 5,800 rpm (for whatever reason, like gearing, track length, and so on) and need to know the section area associated with this engine speed. Inserting these values into our little equation tool computes an intake flow path area of 2.88 square inches.
As also previously discussed in this column, flow path length is a factor in how an intake or exhaust system contributes to overall torque output. The rule of thumb here is length affects how a given torque boost "rocks" about its peak rpm point. It's the section area that relates to the peak point since cross section size (flow rate) links directly to engine speed or piston displacement.

For example, given a fixed section area, the 240 feet/second mean flow velocity will occur sooner as piston displacement is increased. And, of course, the opposite is true if engine size decreases. (We've included a simplified illustration intended to help you visualize these relationships.)

So what about intake and exhaust flow paths of non-uniform cross section? Since we're attempting to stay with the hands-on approach to making these concepts a useful tool to engine builders, tuners, and parts manufacturers, we'll avoid how intake passage taper plays into the issue.

For the sake of simplicity, you can calculate the entry and exit section areas, average the two, and use that number for flow path section area in the equation. While it won't provide the most refined data, you may be surprised at how useful it can be.

On the exhaust side, when using headers with specific "steps" or sudden changes in section area, here's how you can view that subject. When what we'll call an exhaust "pulse" experiences a sudden change (increase or decrease) in section area, there will be a corresponding reaction in a reverse direction.

Again, simply stated, each section of primary pipe that differs from another will generate its own contribution to net torque from the exhaust system. And, as you might expect, the influence of each section's length on the whole is much like the intake side.

Now, where's the value in learning about and understanding this month's topic? If you're trying to evaluate an engine's performance, either on the dyno or track, knowing something about two major factors in overall torque output can help a range of topics, including on-track gearing, chassis set up, and driving technique. Certainly there are other engine components and conditions that affect net torque. But it's also a given that intake and exhaust systems have a major influence in where and how a racing engine operates in its intended speed range.

Can you use this "tool" to identify intake and exhaust system dimensions to optimize their application toward specific operational objectives? Absolutely. Is it possible to size intake and exhaust systems to broaden a net torque curve by increasing the rpm range between their respective torque peaks? Again, absolutely.

Just remember that when you look at an overall torque curve (or data) that displays only one peak, that doesn't mean each system isn't contributing its separate part. I've been a part of tests that helped verify this by literally tuning an exhaust system well beyond a test engine's rpm range to more clearly define torque contribution by the intake system, dimensioned as described in the column you're reading. We then tuned the intake system beyond the available rpm range after re-dimensioning the exhaust system to evaluate its contribution. The peaks for each were remarkably close to the predicted rpm, based on the engine's piston displacement and intake/exhaust dimensions. So the idea works. And when you stop and think about it, it's a quick way to evaluate and match parts to either minimize mistakes, reduce parts investment, or both.

Indycars · Dec 4, 2010

I like the way Jim McFarland writes. It's straight forward in a logical progression thru the subject making it easy to read. That articles was especially interesting in that you could easily do the calculations without having a million dollar lab to get at the data.

grumpyvette · Mar 2, 2011

http://carprogrammer.com/Z28/CylinderHe ... _notes.htm

cylinder Head Development Notes

Intake Runner -

When air travels through a tube, if the air velocity gets sonic, the speed of sound, the airflow through that tube is constant. In other words, once air velocity becomes sonic, you cannot flow any more air. Under sonic conditions, the only way to increase airflow is to either increase the area of the tube or increase the pressure on the feed side of the tube. (http://oldsracer.tripod.com/art2.html)

The difference in an engine is that the air velocity that flow "stalls", or no longer increases with increasing valve lift, is closer to mach .6 rather than mach 1. This is because of things like friction get involved and as the port changes cross sectional area; the flow gets faster through this section.

In order to make HP you need air flow. An engine is just an air pump, the more air you pump, the more HP you will make. As you move more air, the air velocity goes higher and higher with increasing RPM. Once the air velocity gets too high, you canâ€™t flow any more air. Olds engines have very small intake ports.

>There are two ways to talk about port size, most people talk about port size in ccs. This is fine, but what really matters is the cc's divided by runner length. I convert this to an average size diameter of the port. If you look at a Ford 390-428 head (or 352 to 428 head for the people that remember), the ports are very short so the cc's of the port are smaller, even though the average diameter of the port is still very reasonable. I will refer to port volume in average diameter rather than ccâ€™s. The average diameter of the ports is only 1.80" in diameter. This is calculated with a port volume of 187ccs and a port length of 4.5". This length is calculated through the center of the port to the valve opening. For comparison, the Edelbrock heads have an average diameter of 1.71" and a set of ported Batten heads have an average diameter of 1.91". A stock set of "double camel hump" small block Chevy heads have an average diameter of 1.6" and a set of NASCAR Winston Cup heads have an average diameter of 2.04".

The limiting factor for an Olds engine making power is the intake ports on the cylinder heads. With the small port diameter, the air velocity gets very high and the intake ports stall. Most production Olds cylinder heads stall around .550" lift. I have never seen a production Olds intake port that still flows more air beyond .575" lift, most likely; you are not the exception to the rule. You cannot make the ports big enough due to several limiting factors. One is the fact that the intake port is sandwiched in between two pushrod holes. You can only make the port so wide because of this. In addition, one of the head boltholes is also located down in the port and prevents you from making the port big enough. This is why raising the roof of the intake port is so successful, it adds port volume, slowing down the air.

how do I increase volumetric efficiency of my motor?

http://www.wallaceracing.com/chokepoint.php
http://www.rbracing-rsr.com/runnertorquecalc.html
http://www.velocity-of-sound.com/velocity_of_sound/calculator1.htm

Volumetric Efficiency: Is calculated by dividing the mass of air inducted into the cylinder between IVO and IVC divided by the mass of air that would fill the cylinder at atmospheric pressure (with the piston at BDC). Typical values range from 0.6 to 1.2, or 60% to 120%. Peak torque always occurs at the engine speed that produced the highest volumetric efficiency.
keep in mind as rpms increase so do port speeds and volumetric efficiency UP TO A POINT, WHERE THE TIME LIMITATION TO FILL AND SCAVENGE the cylinder limits power
(http://www.superflow.com/support/suppor ... ciency.htm)

First, maximum flow is limited by the valve area. There is a chart in the SuperFlow manual that shows the maximum flow potential. It is based on a flow coefficient of 0.74. Certain head designs are much better than other head designs. But over the years when people just sat there with a valve and a port and tried to make it perfect, they seldom exceeded 0.74 coefficient of discharge (Cd).

In the early days before everybody was flow testing, they just made the port big. In doing so, they frequently made the cross-sectional area too great, even when it had maximum flow. Maximum power is obtained with the smallest port cross-section that will deliver that flow.

If you are really limited by the valve area and youâ€™ve got that all maximized, but your port is too large, the flowbench doesnâ€™t know the difference. It just says, "Yeah, thatâ€™s a good flowing valve." But the transient pulsation in the running engine, the inertia supercharge, and the tuning effects, are proportional to the velocity of the air going down the port. If it is too small, the flow will drop off. Thatâ€™s not good. But if it is not as small as possible, there will be a reduced inertia supercharge effect. The engine can lose 10% or 15% of your power, particularly near peak torque, instead of peak power.

Experiment to determine if the port is as small as it can be, use various size ball bearings â€” 1/4", 5/16", 3/8" â€” and put them on the end of a piece of 0.06" welding rod. Then run the balls up and down the port and watch what happens to the flow. If there are cross-sections where nothing happens, that port is probably bigger than it needs to be at that point. Take some clay and smooth it in, and make the port smaller. If the flow doesnâ€™t change appreciably, the port is probably bigger than it needs to be in that area. There is a relationship between the port area, port volume, and the power produced at various speeds by the engine.

Typically, the port is slightly converging as it comes down from the intake manifold, and the minimum cross-section area of the port is about 80% of the valve area. The ratio varies from engine design to engine design. Oversized ports, if they are too large, will reduce the inertia supercharge effect, which rams the air in just as the intake valve is closing. Inertia supercharge helps provide high volumetric efficiency.

Engines tend to peak when the maximum velocity through the valve at the maximum point in the intake cycle is about 550 to 600 feet per second. At greater velocities, the power drops. The engine will keep getting more and more power until it reaches the point where the "Mach" is 0.55, and then the power drops. You have to increase the airflow, and reduce the Mach number, in order to get power at a higher speed. Mach is ratio of air speed to the speed of sound, about 1080 feet per second at sea level.

SuperFlow recommends that you always use a radiused inlet guide when testing a cylinder head by itself. A radiused inlet guide has a rounded shape to guide the air into the test piece. A sharp edge at the port entrance will cause the air to flow in toward the center of the port rather than following the port walls. The edge acts like it is choking the airflow. The flow difference can be as much as 30% due to the sharp edge effect. The radiused inlet guide directs the air straight into the port with a small loss, just as it would be if an intake manifold was connected. When an operator tests his head without a radiused inlet guide or an intake manifold, his results will be very different than your results. So it is critical to use a radiused inlet guide. The radius should be about half the width of the port. For a 2" wide port, use a 1" radius radiused inlet guide as the minimum dimension. The same radiused guide should of course be used for all comparative tests.

At what speed will the engine develop peak power? Speed determines the intake runner length, the exhaust runner lengths, the cam timing, how to gear the car... All these factors are inter-related. Peak power speed is based on the Mach number again. When Mach is 0.55, the power will peak.

Using a simple equation, peak rpm is going to occur at the flow in CFM per cubic inch of cylinder, multiplied by 1265. For 100 CFM, divide by the cubic inch displacement of that cylinder and multiply it by 1265, and that will give the speed for the peak rpm for the engine. There are some of the production engines that are pretty restrictive that will actually achieve this power at about 10% higher speed. For most race engines, this number is a pretty good one. After a couple of rounds of flow testing, you can see where it is actually occurring. Then you might want to modify this number to fit your specific combination. Any of these formulas can be adjusted to fit a specific engine if required.

The cross-sectional area of most intake ports becomes gradually smaller as the air moves toward the valve. This causes the air to accelerate as it approaches the valve, and actually helps ram more air past the valve into the cylinder when the valve opens. Any sudden changes in the cross-section of the port can disrupt this effect and restrict air flow. Thatâ€™s why port modifications that are made in the area just above the valve must not upset the normal increase in air velocity. The same goes for the exhaust side, too, except here the cross-section of the ports gets larger as the exhaust gases flow away from the valves. Again, the secret to maximizing flow is to have a smooth transition and as few obstructions as possible.

The joint where the intake manifold and cylinder head meet also is a critical area. If the runners in the intake manifold are not perfectly aligned with the ports in the head, sharp edges can interrupt normal air flow and impair performance. Matching up the ports so thereâ€™s a smooth transition from manifold to head will ensure maximum air flow. The same goes for exhaust ports. The head ports must be aligned with the header openings so the exhaust gases can pass freely out of the engine without encountering any sharp edges or obstacles.

Bigger is not always better. Grind away too much metal and you may end up ruining the casting if you cut into a water jacket. But even if you dont grind all the way through, removing metal in the wrong places can actually end up hurting air flow more than it helps. Heres why: The secret to maximizing air flow and engine performance is maximizing volumetric efficiency and air flow velocity.

Big ports with lots of volume will obviously flow more air than a smaller port with less volume - but only at higher rpm. A lot of people dont know that. At lower rpm and mid-range, a smaller port actually flows more efficiently and delivers better torque and performance because the air moves through the port at higher speed. This helps push more air and fuel into the cylinder every time the valve opens. At higher rpm, the momentum of the air helps ram in more air, so a larger port can flow more air when the engine needs it.

When you go to select headers for your car, or chose cylinder heads, you need to shop carefully.
keep in mind that some bbc and some SBC heads have the exhaust port locations raised about 3/4-1.125 inchs higher than standard heads, for better flow while in most cases this does not pose a problem it can place the header collectors high enough to touch the firewall/floor boards in some cases, heres some links that may allow you to find related info

http://www.trickflow.com/search/department/cylinder-heads/section/cylinder-heads/make/chevrolet?N=4294961402+4294965891+4294966157

http://www.airflowresearch.com/

http://www.profilerperformance.com/racing/cylinderheads/bbc-24-heads

http://www.theengineshop.com/products/cylinder-heads/world-productsfoot-big-block-chevy-iron-heads/

http://www.nastyz28.com/bbcmenu.php

http://www.minuit10.net/EngineCode/chevy/BBChevyCylinderHead.htm

http://rehermorrison.com/product-category/components/cylinder-heads/cylinder-heads-big-block-chevy/

http://www.edelbrock.com/automotive/mc/cylinder-heads/chevy/

http://www.dartheads.com/

http://www.brodix.com/

http://www.allproheads.com/

http://www.procylinderheads.com/

http://bigblockchevyheads.net/454-heads

http://www.superchevy.com/how-to/en...206-oval-port-big-block-chevy-cylinder-heads/

http://www.cartechbooks.com/techtips/killerbigblockchevy/

http://www.chevyhardcore.com/tech-s...uide-to-budget-bbc-cylinder-heads-under-2000/

http://www.hotrod.com/how-to/engine/ccrp-0803-big-block-cylinder-heads/

grumpyvette · May 1, 2011

GRUMPYVETTE?
Ive always heard that you should select the smallest port that flows enough to meet your power requirements and Im looking at the 195cc and210cc AFR heads, both flow about what I need but I don,t want to use a cam with more than .600 lift , and IM going to use a SUPERCHARGER so the larger heads main advantage being at those higher lifts , Im leaning towards the 195cc heads,as Im sure the superchargers going to further increase flow rates.
http://www.airflowresearch.com/super-chevy-apr-2010-210cc-sbc.php
this is a no brainer, with a supercharger theres no question the large cross sectional area on the slightly larger 210cc head has an advantage, remember your mechanically PRESSURIZING the port and plenum and runners to well above standard N/A air pressure levels, not relying on the low pressure in the cylinder caused by the piston dropping away from TDC to allow the port to flow, the smaller port becomes a restriction under those conditions compared to the larger port cross section.
keep in mind supercharged applications require a wider LSA and more exhaust duration,both to trap the incoming charge , before it can exit out the exhaust valve and to allow the cylinders to fill more efficiently , as the exhaust needs to close earlier and the longer exhaust duration to compensate for the greater volume of burn gases.

http://www.wallaceracing.com/runnertorquecalc.php
keep in mind that as your throttle blades on the carburetor or EFI throttle body open the plenum vacuum tends to drop and velocity in the ports increase as the rpms increase, and at 6000rpm theres 50 valve open/close cycles per second on each intake port.thats 50 separate intake, port inertia start and stop sequences, the resulting ,intake port reversion, and exhaust scavenging pulses in the headers trying to draw in the intake charge by dropping the exhaust port pressure effecting flow thru the intake ports,
heads are generally flow rated at 28" of vacuum but your engine pulls far lower plenum vacuum at high rpms and with wide open throttle

Grumpy · Aug 21, 2022

Grumpy · Aug 21, 2022

How Valves Seal

Stainless Valves: Do you really need them?

I thought this was interesting info from the Isky website. I can't find where I have SS valves, but a magnet will NOT stick to one of the Brodix IK200 valves. I'm wondering if I should consider buying valve lash caps??? http://www.iskycams.com/techinfo_index.html Click on "Tech Tips 2000"...
garage.grumpysperformance.com

don,t forget to use proper valve spring seats/shims

now you may not need these, on all applications, but aluminum heads can be damaged if the valve spring is run directly on the head surface ,and if the springs base can move around due to harmonics at high rpms it can cause valve control issues and wear issues and they are a good idea on even...
garage.grumpysperformance.com

sellecting valve springs, and setting up the valve train

How do you determine the spring pressure needed to keep the valves under control for a given lift, duration, and max rpm. It might take you several hours to read thru all the links and sub links but its time very well spent as it could save your engine from destruction and save you thousands of...
garage.grumpysperformance.com

more port flow related info

grumpyvette

Administrator

sellecting cylinder heads

port speeds and area

grumpyvette

Administrator

grumpyvette

Administrator

grumpyvette

Administrator

Attachments

grumpyvette

Administrator

grumpyvette

Administrator

grumpyvette

Administrator

grumpyvette

Administrator

grumpyvette

Administrator

Indycars

Administrator

grumpyvette

Administrator

grumpyvette

Administrator

Grumpy

The Grumpy Grease Monkey mechanical engineer.

Grumpy

The Grumpy Grease Monkey mechanical engineer.

How Valves Seal

Stainless Valves: Do you really need them?

don,t forget to use proper valve spring seats/shims

sellecting valve springs, and setting up the valve train

more port flow related info

Administrator

Administrator

Administrator

Administrator

Attachments

Administrator

Administrator

Administrator

Administrator

Administrator

Administrator

Administrator

Administrator

The Grumpy Grease Monkey mechanical engineer.

The Grumpy Grease Monkey mechanical engineer.

How Valves Seal​

Stainless Valves: Do you really need them?​

don,t forget to use proper valve spring seats/shims​

sellecting valve springs, and setting up the valve train​

How Valves Seal

Stainless Valves: Do you really need them?

don,t forget to use proper valve spring seats/shims

sellecting valve springs, and setting up the valve train