port speeds and area

[grumpyvette]

I CAN,T EVEN TELL YOU HOW INSANE SOME CONVERSATIONS I HAVE SEEN GUYS GET EVOLVED IN ARE!
GUYS TELL YOU A 210CC air flow research HEADS GOING TO ABSOLUTELY KILL Torque ON A 383 BUT ITS FINE FOR A 400 SBC, WHAT TOTAL b.s, your cylinder heads port size needs to be selected with both displacement and the intended rpm/power band in mind and a 10% change in engine displacement may or may not require a change in port size, as other factors, like the ports minimum cross sectional area and shape, valve curtain area, cam timing,compression ratio, intake runner length and cross section, and your exhaust header design,etc. will have as large or a larger effect results.
look thru the linked info theres calculators , listed in the links and sub-links that can be used to accurately calculate the correct port cross sectional area, and runner length, matching header config cam timing etc.
theres a HUGE MIS -CONCEPTION out there that its always the larger port cross sectional area on any engine that lacks low speed torque, thats responsible for a loss of low speed torque, in most cases it is the combo of a larger than ideal for the application cam duration and a single plane intake, and larger and shorter headers or a restrictive exhaust having been selected ,NOT the cylinder heads port size.
YES cylinder head port cross section will effect the port velocity, but in most cases if your building a performance street cars engine your better off going slightly larger on port size and slightly conservative on the cam duration. and a good dual plane intake and long tube headers with a low restriction exhaust sure helps.
wider LSA smooths out the idle but it reduces overlap, the increased overlap tends to allow cylinder fill at a bit higher rpm and it also tends to kill off a bit of low rpm torque
keep in mind a cam simply controls PART of the complex sequence of mechanical , inertial flow,and thermal events that effect the engines cylinder filling exhaust scavenging efficiency , the head flow, intake design, efi or carb manifold, plenum and runners, exhaust header design, primairy and collector size and length, exhaust back pressure the fuel air ratio, the ignition timing, and the drive train gearing, the engine displacement, combustion chamber shape valve sizes, the valve seat angles and several other factors have significant effect on the power your likely to see and at what rpm, its available.

The following tables illustrate how variations in lobe separation angle and cam
timing will effect the behavior of the engine in which the camshaft is installed.

EFFECTS OF ALTERING CAMSHAFT TIMING
Advancing.......................................... Retarding
Begins Intake Event Sooner................. Delays Intake Closing Event
Open Intake Valve Sooner ........................Keeps Intake Valve Open Later
Builds More Low-End Torque................. Builds More High-RPM Power
Decrease Piston-Intake Valve Clearance Increase Piston-Intake Valve Clearance
Increase Piston-Exhaust Valve Clearance Decrease Piston-Exhaust Valve Clearance

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.

before as cast

after port clean up intake

before as cast

after port clean up exhaust

Calculating Port Velocity
If you know the cross-sectional area of a given port you can calculate the port velocity based on the bore diameter and the piston speed at any given RPM using the following formula.

Port Velocityfps = (Ps ÷ 60) x (B2 ÷ Ap)

Where:

Ps = piston speed in feet per minute

B = bore diameter in inches

Ap = area of port in square inches

The first part of the formula converts the piston speed to feet per second while the second half relates the bore area to the port cross section. Consider the following example: A 3-inch-stroke 302-ci engine running at 4,400 rpm (torque peak) achieves a piston speed of 2,200 feet per minute at that point. The bore is 4.00 inches and the port cross section is 2.44 square inches.

Pvel = (2,200 ÷ 60) x (4.002 ÷ 2.44) = 240.4 feet per second

viewtopic.php?f=52&t=8460

https://www.gregraven.org/hotwater/calculators/airflow-hp

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

https://www.cartechbooks.com/techtips/cylinder-head-math-for-engine-performance/

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

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


viewtopic.php?f=52&t=8460&p=32923&hilit=curtain+flow+angle#p32923

viewtopic.php?f=52&t=322

viewtopic.php?f=52&t=10602

http://www.strokerengine.com/SBCHeadsFlow.html

viewtopic.php?f=69&t=9879

When you see cylinder heads listed as lets say 177cc or 190cc or 210cc port heads thats a reference to the internal intake port runner volume, and while larger port heads tend to flow more air theres no direct linear link, an exceptional 190cc port can out flow a marginal 210cc port, and the shape of the port and its length also effect its volume, a change in port volume of 5% alone with no other change is almost meaningless it the effect it has on engine torque ,compared the intake,runner design, exhaust,or header configuration, compression and cam timing
valve seat and back face angles ,valve diameter and valve lift and duration effect the flow thru the curtain area

Predicting Horsepower from Airflow
Another SuperFlow-sourced formula along the same lines uses airflow through a complete system to predict peak horsepower. If you have already obtained the appropriate flow values and predicted your peak engine speed, you can use the same flow value to estimate peak power. I first learned of this simple formula from former SuperFlow Vice President Harold Bettes more than twenty years ago and have seen its prediction come pretty close many times. SuperFlow developed power coefficients for each of the most widely used flow bench test pressures. Again, remember that they are only accurate if you have airflow measurements through a complete inlet system.

Horsepower = observed CFM x power coefficient x number of cylinders

Power For Flow at Coefficient Inches of Water

0.43 10

0.35 15

0.27 25

0.26 28

Assuming a cylinder head with manifold and open carburetor attached, we observe a net flow of 225 cfm when tested on a flow bench at 28 inches of water. The corresponding power coefficient is 0.26.

Horsepower = 225 x 0.26 x 8 = 468

For best results you would want to verify flow numbers through several different ports.

PORT MATCHING THE INTAKE RUNNER EXIT TO THE CYLINDER HEAD PORT ENTRANCE USUALLY HELPS REDUCE RESTRICTIONS TO FLOW RATES, AND REDUCES FUEL/AIR DISTRIBUTION ISSUES

keep in mind there are tools that can be used to measure air pressure at different points in an intake port that can be used to accurately calculate air flow speeds, and youll moss a ton of info if you don,t read the sub links

on the better 23 degree SMALL BLOCK AFTERMARKET HEADS THERE'S ABOUT 5.5 INCHES OF INTAKE PORT LENGTH ON AVERAGE FROM INTAKE GASKET TO THE BACK OF THE INTAKE VALVE AT THE FAR EDGE

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.circletrack.com/enginetech/1 ... ch_engine/
calculate horse power from intake port flow rates
http://www.wallaceracing.com/calcafhp.php

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

http://www.wallaceracing.com/ca-calc.php

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

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

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

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

http://www.wallaceracing.com/area-under-curve.php

http://www.wallaceracing.com/piston-speed-velocity.php

http://www.wallaceracing.com/header_length.php
related info, that you might need
http://garage.grumpysperformance.co...heads-for-small-block-chevys.3293/#post-26213

http://garage.grumpysperformance.com/index.php?threads/what-are-these-heads.4702/#post-12742

http://garage.grumpysperformance.co...-by-step-guide-with-pictures.5378/#post-71848

http://garage.grumpysperformance.co...ther-efi-intake-manifold-info.431/#post-26322

http://garage.grumpysperformance.com/index.php?threads/porting-can-help.462/page-3#post-59145

http://garage.grumpysperformance.co...ads-tuned-intake-turbulence.12998/#post-67611

Volume (CCs) of Head Gasket
CCs of Head Gasket = Bore x Bore x 12.87 x Thickness of Head Gasket
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
http://users.erols.com/srweiss/calccsa.htm

Your RPM computed from your Cross Sectional Area of 1.95
(the smaller AFR HEADS)
and Bore of 4.03 and Stroke of 3.75 is 5,569.12 .

Your RPM computed from your Cross Sectional Area of 2.05
(the Larger AFR HEADS)
and Bore of 4.03 and Stroke of 3.75 is 5,854.72 .
you,ll barely notice the about 300 rpm shift in the power band on the lower part of rpm range but appreciate it much more on the upper edge of that power curve


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
http://www.superchevy.com/how-to/en...-0902-chevy-engine-port-variations-measuring/
http://www.hotrod.com/articles/choosing-the-right-camshaft/
http://garage.grumpysperformance.com/index.php?threads/bits-of-383-info.38/

Last edited: 1 minute ago

keep in mind in most cases youll want to select a intake port that will allow the highest air flow rates without getting into port stall or making the port cross sectional area restrict flow.
youll find that the average cylinder head intake gasket is about 10%-15% LARGER IN CROSS SECTIONAL AREA THAT THE NARROW SECTION OF MOST INTAKE PORT EITHER DUE TO THE PORT RESTRICTION NEAR THE PUSH RODS OR VALVE THROATS.
ideally youll want to select a port cross sectional area that will provide near 300fps in air flow rates at or near the intended power peak, which in most performance engines will be close to reaching critical piston durability rpm levels.
on most engines using good performance components thats about 4300fpm in piston speeds.

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

valve seat and back face angles ,valve diameter and valve lift and duration effect the flow thru the curtain area

keep in mind that valve may be forced off its seat, too full lift and re-seating 50 plus TIMES A SECOND at near 5500 rpm, so theres very little TIME for gases to move through the very restrictive space between the valve seat and valve edge

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, thus it makes a great deal of sense to push the valve lift a bit over .500, and have an intake port that is at least 3.2 square inches in cross sectional area, if you want to maximize flow on a 2.02" intake valve

notice its right where the roller cams lobe design maximized the extra air flow potential that is the most effective flow area during the whole valve flow curve
and yes it frequently helps to match a roller cam to roller rockers as the reduced friction further helps the engines durability and ability to easily cope with faster valve train component acceleration, that tends to reduce heat and wear.

http://www.circletrack.com/techarticles ... ewall.html
the guys that tell you you should have used 195cc heads on your 383,sbc , and will all point to the larger 210cc head as having lower port flow speeds,...WELL, while thats true, BUT ONLY UP TO A POINT, AND IT MIGHT NOT, BE IN YOUR COMBOS BEST INTEREST TO GO WITH THE SMALLER PORT SIZE the amount of the port flow reduction is all but meaningless, IN MANY APPLICATIONS 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,
repeating 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 between those two heads in cross sectional area,is about 1%
the 210cc heads superior,provided your trying to maximize the combos power potential and are running the engine up into its peak potential power band, PORT FLOW SPEEDS WILL BE EQUAL OR HIGHER JUST 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 about .550 LIFT AND OVER about 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.
now obviously if your running a much smaller cam duration,in the 220-230 @50 lift and under .530 lift low 9:1 or lower compression and a restrictive intake, there's not much point in installing killer heads where you'll never get close to the the larger ports full flow potential

many guys will tell you that selecting oval port heads is better on a street car engine, and they generally have a point, yet depending on compression ratio and cam used you may never notice any loss of low rpm torque, if you select a reasonable size rectangular port head and matched components ,this is one of the huge semi-myths about big block engines.
while its true that the low rpm torque does tend to be reduced with stock oval port heads vs stock rectangular port heads ,its also true that the compression, intake manifold, cam timing,rear gearing and header designs all change the results and its very easy to build a rectangular port engine that destroys tires, and theres a huge range in size of the ports in BOTH oval and rectangle port aftermarket heads

http://www.carcraft.com/techarticles/cc ... ewall.html
read the article

Peaks and Averages
................Avg. TQ Avg. HP Peak TQ Peak HP
Iron .. ........541.1 475.0 595 .........521
Edelbrock 582.1 514.9 618 ........582
Dart .......... 584.2 517.7 615 .......595
TFS ................590.3 522.5 626 ... 595
Brodix .....590.8 ........523.0 626 ........597
here read thru these LINKS THERE'S LOTS OF GOOD INFO! and some CALCULATORS YOU CAN USE, and remember the basic concepts apply to both bbc and sbc engines but naturally the port sizes and flow rates and cam timing needs to match the application
a few hours spent reading links can save you a great deal of wasted time, and a great deal of wasted money

http://www.airflowresearch.com/articles ... 1/A-P1.htm

http://www.tmossporting.com/tabid/1805/Default.aspx

http://racingfeed.com/downloads/chevy_flow_data.pdf

http://www.strokerengine.com/SBCHeadsFlow.html

http://www.wallaceracing.com/area-under-curve.php



http://www.j-performance.com/index.php? ... view&id=48

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://www.s262612653.websitehome.co.uk ... /heads.htm

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

http://www.wallaceracing.com/max-rpm2.php



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

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

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



http://www.wallaceracing.com/max-rpm2.php



http://www.j-performance.com/index.php? ... view&id=28



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

http://www.jsme.or.jp/esd/COMODIA-Procs ... 4_P535.pdf

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

http://www.slowgt.com/Calc2.htm#MinCross

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

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



http://airflowresearch.com/articles/article115/A-P1.htm



http://airflowresearch.com/articles/article031/A-P1.htm

http://garage.grumpysperformance.com/index.php?threads/virtual-dyno-software.2301/#post-53646

http://www.chevyasylum.com/chp/



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

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



http://www.brodix.com/media/images/page_2.jpg

http://www.dartheads.com/customer_servi ... .php?qk=34

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



here's 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

DYNO DON POSTED THIS BIT OF INFO

"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
"

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

your ports cross section selection should depend on the cars gearing , displacement, compression ratio,and average rpm range and the cam timing you'll be using, a 12:1 cpr 383 with a .650 lift cam that spends most of its time in the 4500rpm-7500rpm band will take a larger port cross section , than a 9:1 cpr 383 with a .450 lift cam that spends most of its time in the 1500rpm-5500rpm band. or a 350 will work out best with a 180cc port vs a 195cc or even a 200cc port size, ok I understand WHY your thinking that way but Id doubt you've done the math if you still hold that position, here is why, the 195cc port has a cross sectional area of about 2.15 sq inches MAX, the 180 cc ports run close to 2.1 sq inches ,MAX MOST ARE SMALLER IN CROSS SECTIONAL AREA, but think about this, a 2.02" intake valve that's .450" off its seat has a flow curtain of about 2.86sq inches
2.02" diam x pi 3.147 x .450"=2.86sq inches even at that low lift.
the intake runner design and intake plenum and the cam timing, displacement and compression ratio will have far more effect on the port flow than a simple swap from 180cc to 200cc in the head port size

it does absolutely no good to place a cylinder head with with a port cross sectional area thats larger than the intake port that feeds it,beyond the intake runner exit, in a combo as all the abrupt increase in port cross section does is cause increased turbulence, and a sudden loss of port air flow speed and that tends to cause fuel to drop out of the airflow or at least disrupt is even distribution
in an ideal world ports reduce cross sectional area bye about 3% from entrance to the valve pocket, and the port cross section in the heads a bit smaller than the intake runner.
the port flow is limited by the ports smallest cross section not its largest

http://www.wallaceracing.com/max-rpm2.php

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



http://garage.grumpysperformance.co...out-profiler-cylinder-heads.10065/#post-70886

making even the larger port a restriction, and in any case a difference of about 3%in cross sectional area is in effect meaningless to flow rates,
KEEP IN MIND that a good deal of the power in any engine combo will be the result of how efficiently you blend factors like,
EFFECTIVE COMPRESSION,vs fuel octane
CYLINDER HEAD FLOW rates vs displacement
and
EXHAUST scavenging efficiency.(cam timing)
theres a good deal of math involved, that can be used to accurately predict the results but there's also an ART and SKILL to tuning and engine assembly, and experience goes a long way there.
and yes a slight mis-match of components, not getting the clearances correct, or a few degrees of cam duration,plus or minus from what the engine needs, and a few cfm difference in intake or exhaust restriction,flow, a few extra fractions of an inch of valve lift, a better or worse multi angle valve job and your up or down 60-80 hp...

port throats generally run 80%-85% of total valve diameter because you need to maintain sufficient valve seat contact area to allow sealing and cooling and some wear during operation

 

[grumpyvette]

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 calculators, 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 that's the restriction to flow
IDEAL FLOW FLUX another critical intake pumping process parameter that has been discovered over the years of ENGINE PRO SOFTWARE DEVELOPMENT is the maximum intake flow per unit of area that can be obtained on the flow bench when tested at 28 inches of H20 .
This value is calculated using the intake throat minimum cross sectional area (CSA) which is usually located just up stream of the intake valve seat insert or seat ring.

THINK THROUGH YOUR OPTIONS AND THE COMPLETE COMBO,
I see guys have long discussions about things like the difference in port cross sectional area or the best connecting rod length, to use, no one factor is going to make your engine totally dominate the competition, its a combo of small almost insignificant individual component choices being made and a good deal of time and effort taken during the assembly and clearancing work, that stack up to give you or prevent you from maximizing the engines performance.
you may not even think about factors like polishing crank journals, or valve train geometry or intake runner cross sectioinal area or length ,or intake runner port matching or surface finish, but the combined effects of your choices and components selected do mater!
look guys I think a good deal of this discussion is missing the point here, Ive built well over 150 engines in the last 45 years, (I lost cound decades ago)
but I can assure you that longer rods and the easily verifyable slight increase in dwell time, the longer rods produce will be totally meaningless UNLESS, you design the engine for and select components too take full advantage of the minor increase, by carefully calculating the REQUIRED compression ratio,fuel octane required,all the factors related to the cam timing,(duration,lift, LCA) you calculate and build and install, and tune the engine for , a matched exhaust header scavenging (header primairy length and diameter plus collector design) and the intake runner length and cross sectional area, to maximize the cylinder scavenging effects, plus you match the fuel/air ratio, and ignition advance curve, to maximize that longer dwell times potential advantage.

its been my experience that a properly done valve job with 3-5 angles and its the port throat and valve guide area under the valve,
yup! hard to beat the value in hp/vs cost outlay,
in a well designed and carefully assembled, BBC
if your willing to build a fairly high compression version that runs race octane fuel or E85 you can get amazing power, Ive build several dozen 496 BBC engines over the past 4 decades , and getting 600hp-800hp, or more or more depending on your checking account balance and how willing you are too hear it scream in agony, as you rip its heart out, if youve got a reasonable budget is no big challenge:laughing:

[
that is a huge factor in its potential flow, but remember the header scavenging and compression and cam timing all effect the potential results, while the article may promote the 50 Deg valve seat angle a change in cam timing port shape or exhaust scavenging or rocker ratio, various porting tech, piston too combustion chamber mods, heat reflective coating, merge collectors , would have a more noticeable effect on the engines power curve in my opinion.
theres a reason the early SBC 23 degree heads with similar valve size to the later 18 degree heads can,t keep up, and its not the valve seat angles, theres a reason the later vortec heads with similar port volume and valve size to the mildly ported corvette fuelie heads out flow those early heads that were designed in the 1960s , and its not the valve seat angles!
and the biggest reason the 50 degree valve seat angle is not commonly used is long term durability, valves wear and seats wear and as the valve sinks deeper into the heads combustion chamber flow is reduced , now on a race engine that will be dis-assembled every season that may not be a huge issue, but if you expect to get 50K-100K miles its something you'll want to think through.

blending the valve seat into the port throat with a 3-5 degree multi angle valve job, and porting the bowl area and valve guides,will have far more effect on power than a couple degree change in valve seat angle

read this related thread and sub linked info
http://garage.grumpysperformance.com/index.php?threads/valve-seat-angles-and-air-flow.8460/

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

the valve seat throat area as a percentage of the intake valve diameter effects the port flow rate, yes the port cross section and angle also effect flow rates and larger valves and larger throat areas with less restriction obviously have some potentially lower flow restriction.
SO HOW do you MEASURE THEN??
lets do a bit of math, and keep in mind that a correctly designed header and exhaust system, if matched to the correct cam timing can significantly increase the engines potential power/rpm band
port cross sectional area can be measured and the stall speed , accurately calculated, as can the required matching header configuration, and cam timing, yeah! it takes some reading but the infos readily available

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

USE THE CALCULATORS
http://www.rbracing-rsr.com/runnertorquecalc.html
http://www.wallaceracing.com/chokepoint.php
http://www.wallaceracing.com/header_length.php
http://www.superchevy.com/how-to/en...-0902-chevy-engine-port-variations-measuring/
http://www.hotrod.com/articles/choosing-the-right-camshaft/
http://garage.grumpysperformance.com/index.php?threads/bits-of-383-info.38/

if you were to look at a performance big block chevy cylinder head your largest standard intake valve size is either a 2.19" or in a few cases the larger 2.3" valves
a bit of math shows that you won,t reach the max potential flow until valve lift reaches or slightly exceeds about .575-.600 inches of lift with a big block chevy
and a bit more math suggests a minimum of 4.2 square inches of port cross sectional area would be about ideal to match that potential flow,
if you built a 496 BBC stroker that 4.2 SQ inch port would max out at about 6000 rpm and would be best matched with a single plane intake and a cam with a tight 105-106 LSA

http://www.wallaceracing.com/Calculators.htm

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

port cross sectional area has far less effect on the engines low rpm and mid rpm torque than the displacement and compression ratio.
I can,t begin to tell you the number of times Ive grabbed snap gauges and a dial caliper and got questioned about what I was measuring when checking port throat restrictions or runner cross sections.
and in case some guys still don,t grasp it the point is that your dealing with a rather complex system with several potential restrictions and simply throwing a good flowing intake on an engine or increasing the rocker ratio may or may not provide an increase in flow potential, the result depends on how the rest of the components flow and react to the component being changed or the mods you've done, there's always several components that act like weak links in the chain, so locating those and improving those gets the best results, but of course once they are radically improved other components can become the new weak link or restriction.
so your trying to maintain a balance that potentially allows you to reach and exceed the power goals while hopefully not going bankrupt

keep in mind the big block 396 engines back in the 1970s muscle car ear had 255 cc intake ports that were a bit larger than the 155-165 cc SBC ports on the slightly larger displacement 400 sbc, ...have you ever wondered how almost a 100cc difference in intake port volume was used on the two similar displacement size engines,
yet both made rather similar lower and mid rpm torque?

http://garage.grumpysperformance.com/index.php?threads/port-speeds-and-area.333/

http://garage.grumpysperformance.com/index.php?threads/port-and-runner-math.148/#post-34936

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

READ THRU THESE LINKS
viewtopic.php?f=52&t=796

viewtopic.php?f=52&t=462

viewtopic.php?f=52&t=322

viewtopic.php?f=52&t=181

viewtopic.php?f=52&t=5078

viewtopic.php?f=52&t=8460&p=29682&hilit=head+flow+numbers#p29682

viewtopic.php?f=55&t=624&p=28122&hilit=head+flow+numbers#p28122

viewtopic.php?f=38&t=1099&p=26215&hilit=head+flow+numbers#p26215


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 scavenging , 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

READ THIS ALSO

viewtopic.php?f=3&t=1817&p=4699&hilit=rigged#p4699

I think this may help

http://www.wallaceracing.com/Calculators.htm

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

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

http://www.superchevy.com/how-to/projec ... ock-build/

Cylinder Head Runner Volume
http://www.racingheadservice.com/rhs/cy ... olume-faq/
Although Racing Head Service® offers many different intake runner volumes in its cylinder heads, chances are that only one or two of them are appropriate for your application. When it comes to deciding which cylinder heads to order, it is important that you make a realistic judgment of your intended use for your vehicle.

Remember that velocity produces low rpm torque, and flow produces high rpm horsepower. So that 170cc cylinder head that you’ve been looking at -with its smaller, higher-velocity runners and valves, is going to accelerate well from a stop, produce lots of low speed torque, and be a great performer below 6000 RPM (which covers about 97% of all street-performance scenarios), but it may not reach the peak RPM you’d want in say, a drag race engine. Conversely, that high–flowing 235cc Small Block Chevy cylinder head that your friends tell you is all the rage at the local track is going to help your engine to rev like crazy and produce a ton of upper rpm horsepower, but it won’t build power below 3500 RPM -making it virtually unusable on the street.

Which is the correct way to go? Most experts will tell you that the answer is not “bigger is better”, but rather that you should run the correct heads for your application with components (cam, intake, exhaust system, etc.) that are designed to work with them. So if you’re looking to build an all-out race car that will never see street duty, that 235cc head with compression, cam, induction, and drivetrain to match will have you winning races in no time. If you just want to get an extra 20 or 30 horsepower out of your street vehicle, and you aren’t planning on performing 4000 RPM launches anytime soon, then that 170cc head is probably the best choice.

The tables listed below will offer some general cubic inch and RPM guidelines to consider when selecting the intake runner volume of your new cylinder heads:

 

[grumpyvette]

of course you'll want to match the heads you select,
to the intended rpm/power range and application and match the cam timing, compression ratio, and drive train gearing, etc.
so lets discus the current car/truck weight, transmission, tire size, rear gear ratio and what your intended goals and budget limitations are, as a start point.
the last thing you'll want to do is select parts that may cripple or restrict the engine performance by mis-matching components or selecting parts on price alone, we all work on limited budgets,
but its will pay big dividends in power produced too carefully select matched components
and generally the biggest mistake is mis-matching heads, intake and cam combos or scrimping on the quality of the components used,
a couple extra hours or even days spent in detailed of research may prove critical, in fact anything less than buying and reading through several books and reading a couple dozen links and all the sub-links is very likely to leave you missing valuable and critical info youll need later, and thats usually going to cost you wasted time and cash.
the big mistake's most people make is in not selecting the correct cam, to match the displacement and compression and drive train gearing or selecting a restrictive cylinder head or intake that does not match the intended power range
you should read these thread with a calculator and pen and pad to take notes
if you ignore the sub-linked info your ignoring 3/4 of the related useful data.

yes all the linked info below looks over whelming but ,
youll be amazed at the detailed info and,
the mistakes you can avoid by reading carefully and asking detailed questions, thus saving money and time
http://garage.grumpysperformance.com/index.php?threads/sellecting-cylinder-heads.796/

http://garage.grumpysperformance.com/index.php?threads/semi-fool-proof-cam-sellection.82/

http://garage.grumpysperformance.com/index.php?threads/first-hotrod-build.12902/#post-67005

http://garage.grumpysperformance.co...ing-a-383-sbc-combo-planing.12168/#post-58778

http://garage.grumpysperformance.com/index.php?threads/bare-minimum-tools.11026/#post-48785

http://garage.grumpysperformance.com/index.php?threads/matching-parts-and-a-logical-plan.7722/

http://garage.grumpysperformance.com/index.php?threads/what-to-look-for-in-a-good-engine-combo.9930/

http://garage.grumpysperformance.com/index.php?threads/another-383-build.12786/

http://garage.grumpysperformance.com/index.php?threads/383-information-overload.11137/

http://garage.grumpysperformance.com/index.php?threads/a-383-build.10991/

http://garage.grumpysperformance.com/index.php?threads/impersonator.9600/

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

http://garage.grumpysperformance.com/index.php?threads/port-speeds-and-area.333/

http://garage.grumpysperformance.com/index.php?threads/valve-seat-angles-and-air-flow.8460/

http://garage.grumpysperformance.com/index.php?threads/tbucket-engine-project-dart-shp.3814/


READ THRU THESE, LINKS BELOW AND THE ONES EARLIER IN THE THREAD,theres a great deal of info you can use
viewtopic.php?f=52&t=2077&p=44546&hilit=ccing+heads#p44546

viewtopic.php?f=52&t=2630&p=6788&hilit=+shrouding#p6788

viewtopic.php?f=52&t=181

viewtopic.php?f=52&t=528

viewtopic.php?f=52&t=401

viewtopic.php?f=52&t=796

viewtopic.php?f=52&t=148

viewtopic.php?f=52&t=8460

viewtopic.php?f=52&t=975

viewtopic.php?f=52&t=322

viewtopic.php?f=52&t=534

viewtopic.php?f=52&t=389

viewtopic.php?f=52&t=965

viewtopic.php?f=50&t=1266

viewtopic.php?f=71&t=741

 

[grumpyvette]

ok basics, you can use the calculator links above in this thread to get a better grasp on figures.....

lets look at a typical oval port bbc HEAD,

a valve flows only when its open enought to allow air to pass between the seat and edge of the valve, and since it takes a bit of time for inertia to overcome the movement of the mass thats usually at about .004-.006 lift, on the intakes, exhaust valves are under far more pressure than the 14.7 psi that atmosphere air provides so they can be smaller and still flow well..

Valves open and close much faster tham most guys realize, at only 1000 rpm, the intake valve, opens and closes 8.3 TIMES a second, at 7000 rpm thats 58.3 times a second.

the valve throat area can rately exceed 90% of its dia. and 85% is far more comon.
at some point in its lift the area between the outer valve seat and the lower valve surface or the curtain area that forms a theoretical cylinder wall reaches the same total surface area as the port throat and further flow increases drop off rapidly past that point.
On a 2.2" valve that throat area where the valve seats is probably no larger than about 2" in dia. and has about a 3.15 sq inch area, a 2.2" valve has a perimeter of about 6.9" so a lift of about 0.45" will match the throat flow rates.

obviously you want to reach and exceed that lift point durring the cylinder filling process to maximize the port flow, potential, and hold the valve open at that lift or higher durring peak flow.

max port flow rates are usually reached approximately at or just after the piston passes the 90 degree arc point in its downward rotation.

port angle, cross sectional area, runner length , PLENUM VOLUME, RUNNER ANGLE , CARB VENTURIE SIZE AND LOCATION,and seat and valve design, combustion chamber shrouding, displacement, header scavaging ETC. effect the efficiency of the flow into the cylinder.

TIME, not port size or valve size becomes a significant restriction to flow in a N/A engine at some point

 

[grumpyvette]

btw, before reading thru this, remember that car weight, rear gear ratio,carb size , cam timing, valve size, header design, converter stall speed transmission gearing and tire diam. all effect the correct choices,
As the head flow rates and cross sectional area get larger in relation to the displacement they feed,the need to use extended duration cams and large plenum areas under the carb tends to get a bit smaller, or lower, at any given rpm level, simply because it takes less time for the port flow to fill the cylinder. but also keep in mind that larger ports are usually designed to run at HIGHER RPMS and use larger matching cam timing to use that extra flow potential, so youll usually be operating the engine at a higher average rpm band which tends to require a matching increase in the cam duration because of the shorter TIME available for that higher flow rate port to flow air/fuel mix into the cylinders.

lets say you have a 11.5:1 compression ratio 540 BIG BLOCK CHEVY
and youve got a choice of some stock but reworked 260cc ported oval port heads that flow 320cfm, at .650 lift and a set of TRICKFLOW 360cc heads, that flow 410cfm,at .750 lift
neither is IDEAL for the application, but EITHER set of heads can be helped a good deal by matching the cam timing and intake sellection and drive train gearing, and either head can produce decent hp/tq..
it should be rather obvious that the smaller heads will require a single plane intake and probably a cam in the 260-270 duration range to maximize the power curve, the larger heads might work better with a slightly lower duration 250-260 duration range and may or may not work best with a dual plane intake to boost port speeds, and cylinder fill efficiency.
but the oval port heads will tend to have a lower torque peak. due to the comparatively restricted flow rates.

were back to use of the calculations, and measuring the port cross section and flow rates, in the linked info above in the thread or here.

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

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

viewtopic.php?f=52&t=322

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

http://www.j-performance.com/index.php? ... view&id=48

heres a good example of fairly large 340cc port head BBC engine potential with a relatively mid range cam, and 10:1 cpr for a BBC of that size

http://www.edelbrock.com/automotive_new ... _675.shtml

 

[grumpyvette]

http://www.hotrod.com/how-to/engine/0906phr-10-questions-chevy-big-block/

interesting article by
mike-cfm


Understanding the benefits of cylinder head porting

Air and fuel equal power. Yes it’s just that simple… or is it? We’ve all heard the adage “an engine is an air pump”. Theoretically; the more air and fuel that pumps through it, the more power it will make. While this is true for the most part, it is a bit more complicated than that. Engines are a nightmare of in-efficiency and parasitic loss; and builders continually strive to reduce these losses. In this article I’m going to lean towards the efficiency side and discuss cylinder head modification to promote power production.
While casting techniques have improved dramatically over the years, it’s still not a perfect process. Core movement and shrinkage are just two of the problems foundry’s face when producing cylinder heads. This leaves room for improvement through porting. So how does porting improve the airflow and power production of a cylinder head? First let’s take a look at what makes one tick. Some of the leading factors in cylinder head efficiency are; size, shape, flow, volume, valve diameter, valve job, and valve angle. I’ll start by discussing size and volume. These may sound like the same thing, but are actually quite different. Size refers to the minimum cross section, or the smallest window in the port defined in square inches (generally found in the pushrod pinch). Volume covers the complete area of the port defined in cubic centimeters. Volume is used to compare similar design heads for the same make of engine, while cross section is used to compare heads of all makes. Engine size, RPM, and power adders directly affect what the cross section and volume of a head needs to be. The shape of the port has one of the largest effects on overall engine acceleration. Sounds odd right? The shape? It’s true; shape promotes velocity, or air speed, through the port. Velocity above all else will make the head most efficient at producing usable power. Valve diameter, throat diameter, valve job, and valve angle are all crucial in allowing air to pass around the valve itself into the cylinder. Last, but not least, flow comes into play. It’s preached the most in all racing circles and flow does have its place, but without shape, cross section, and volume factored in it means little. Like I stated before, velocity is king in making power.

With a basic understanding of the makeup of a cylinder head, let’s move on to the benefits of modifying one. There are many common mistakes and misconceptions about how cylinder heads effect power production. Simply assuming that the biggest, highest flowing head will make the most power can lead to thousands of wasted dollars. I cannot stress enough how important proper port sizing is to optimum power production. Ideal average airspeed through a very efficient port will fall between .45 and .55 Mach, or roughly 550 feet per second on a live, running engine. It takes the correct size and shape of a runner to ensure the engine experiences these average velocities. It is quite possible for a head to gain flow on the test bench, but actually loose velocity and in turn, power. One important thing to remember is that the port not only moves air, but also fuel. Keeping that fuel in suspension is an absolute must to promote power. An experienced head porter will design a port profile based around all needs of the engine; taking into account the drive train, vehicle weight, and its intended usage. With these things considered, and a proper execution of such, the engine should see gains in both power and acceleration. It begins with a precise cut on the valve seats. It’s beneficial to use multiple angles breaking at least every ten degrees, but no more than fifteen on the intake seat. This promotes fuel suspension as a radius cut will allow fuel to fall out and go unburned. A radius cut however, works quite well on the exhaust seat. Moving into the port the throat should be approximately 90% of the valve diameter while the bowl can be opened to 110%. This completes the proper venturi effect around the valve. This is very important as the valve is the biggest restriction in the port. Shaping the guide, using a gentle radius in the corners, and rolling the short turn into the throat will all promote additional flow and air speed.
Now enough of the blah, blah, blah! Let’s move on to a real life example with before and after test results. For this example I’ll talk about a typical 540” Chevrolet with a single Dominator using a 345cc aluminum head. This engine utilizes a .775” lift roller cam and squeezes it with a 13.5:1 compression ratio. It powers a 3200 lbs stock suspension car on 10” tires with a 2 speed automatic transmission. Using the techniques described in this article the heads were modified and improved as shown in the charts below.





Flow Bench Test
Lift Stock Intake / Ported Intake / Stock Exhaust / Ported Exhaust
.200” 138 .........../ 167............. / 110 ................ /118
.300” 213........... / 242............. / 146 ................./ 158
.400” 276........... / 292 ............./ 188 ................./ 202
.500” 328........... / 345............. / 217.................. / 239
.600” 365........... / 382 ............./ 241 ................../ 260
.700” 382........... / 400 ............./ 256................... / 281
.800” 387............ / 415 ............/ 267.................... / 299

Dyno Graph
RPM Before HP / After HP / Before Torque / After Torque
5500 668.7........ 710.3 ............658.2 ..........662.1
5800 722.4 ........ 742.7 ............665.3.......... 671.5
6100 747.0........ 796.7 ............670.4 ..........688.4
6400 778.3........ 822.4............ 672.1.......... 685.0
6700 789.3........ 847.5............ 661.0.......... 676.7
7000 796.6 ........ 862.7............ 652.3........... 655.8
7300 780.2 ........ 871.3............ 636.4.......... 646.4
7600 767.8 ........ 862.7 ............608.1.......... 621.2

On track performance
Before...................... After
9.63 @ 140 mph 9.18 @ 146 mph


As you can see the heads gained in flow, the engine gained in power, and the car went faster. The average measured airspeed increased by 30 feet per second at 28” of water. Translated into live running engine conditions, this calculates to a gain of roughly 65 fps. This gain moved the numbers right into the optimum airspeed range of 0.5 mach. The engine efficiency also improved as show by fuel consumption during the dyno test. The engine made more power using less fuel. The numbers don’t lie. Given proper execution, porting will improve a cylinder heads numbers every time.
__________________
Another quick head article
I didn't have time to go into a lot of detail, I will talk more about the benefits of SB2 heads at a later date.


SB2.2 heads – NASCAR’s gift to the small Chevy

A NASCAR engine is one of the most efficient power plants in all motorsports. Next to the NHRA Pro Stock engine it’s the most technologically advanced domestic V-8. A NASCAR engine makes as much as 2.4 horsepower per cubic inch through a restricted inlet and utilizing a flat tappet cam. These engines must also endure over 500 miles of 9500 rpm torture. The mega-dollar budgets of the teams provide for a slew of well researched parts with top notch development. Just because these parts were designed to go in circles doesn’t mean they can’t be slightly modified to fit a drag racing engine. The SB2 head has seen a few different versions since its inception. I’ll discuss the latest and best version, the SB2.2. This head has had years of testing, re-design, and improvement. All of this testing done with near unlimited budgets and the most advanced equipment possible. As you can imagine… these things are pretty darn good.
Most racers are un-aware, but SB2.2 heads will bolt on a standard Chevrolet block. Yep, no need for an overpriced, custom machined piece. Heck, even a plain old stock 400 block will work. They do require several SB2.2 specific parts, but nothing exotic or beyond the normal needs of any engine. Beyond the head assemblies themselves the SB2.2’s require their own cam, rockers, valve covers, intake manifold, valley tray, pistons, and headers. Any of the parts listed are readily available through various outlets.
Let’s take a look at the specifics of the head. While conventional small block Chevrolets use a 23 degree valve angle, the SB2.2 uses an 11 degree intake valve angle and 8º exhausts. The intake valve is also canted at 4 degrees towards the bore centerline. With these angles the intake valve actually moves away from the cylinder wall during the lift cycle. This allows for a much larger valve as well as a shallower chamber. Port volumes for the SB2 are much larger than traditional small block heads. While a typical aftermarket 23* intake runner may fall in the 215-230cc range, the SB2.2’s often fall between 280-300cc. Now don’t be fooled by these numbers. The intake port may sound huge by comparison, but it is much higher and longer than a factory layout and in turn has a larger volume. When comparing heads of different design for the same engine it is more important to use the minimum cross sectional area, or the smallest area of the port. It’s very difficult to produce adequate cross sections for engines over 400” with 23* heads. Pushrod bulges and low port locations on 23* heads often become a restriction on larger engines. SB2.2’s on the other hand have high ports with offset pushrods and are capable of feeding even the biggest small blocks. The valve layout is a bit different than standard with the outside cylinders intake and exhaust valve positions being reversed. The intake ports are also spread, but not symmetrical. The overall concept of the head design was to optimize the use of a single four barrel manifold by pointing the runners toward the center of the engine. Even with this purposeful design the heads do still lend themselves worthy of a well prepared tunnel ram intake with two carbs. I’ve included a chart for a direct comparison a factory style head to the SB2.2.
The potential of the SB2.2 is overwhelming. With intake flow exceeding 400cfm these heads will support a large amount of power. It is quite common for a 440” engine with two carburetors to make in excess of 1000 horsepower using a well prepped set of SB2.2 heads. Dollars spent can also be quite reasonable when they are purchased in kit form. SB2 experienced shops such as M&M Engines in Indianapolis sell top end kits in various forms starting around $5000. A similar 23* setup would only run about $1000 less. That’s dollar per horsepower value anyway you look at it. Both boost and nitrous friendly as well, SB2.2 engines have been dyno tested at close to 3000 hp. As you can easily see these heads work!

23 degree / SB2.2

IN port volume

200-230cc / 270-310cc

Min. cross section

2-2.3” square / 2.4-3.2” square

Chamber volume

64-76cc / 34-50cc

IN valve size

2.02-2.100” / 2.15-2.2”

Max ave. IN flow

300-330cfm / 400-440cfm

Power potential

650-750 / 900-1050

Kit cost

$6500 / $8200


Kit includes: Complete ported heads (SB2 heads use titanium valves), shaft rockers, sheet metal valve covers, ported intake, custom pistons, rings, roller cam, roller lifters, pushrods, all bolts, all gaskets, valley tray (SB2) header flanges (SB2)
__________________
http://www.cfmperformance.com (317) 627-4186

http://mmcompetitionengines.com/Flow Numbers.html

 

[87vette81big]

Grumpy,
Can you explain how professioal engine builders measure actual airspeeds inside of running engine?
Induction side and intake ports.
Everyone is allways concerned with big airflow cfm numbers.
True it builds big high rpm horsepowet at WOT. But on the street we seldom get to use it most of the time.
I have known a few professioal headporters, been told a cylinder head with a highly efficient intake port has very high velocity. Something you promote likewise. Many cylinder heads as tested on a flow bench will exhibit big cfm airflow but also have bad turbulance present. With a flowbench operating, a loud drumming noise is preset, oscillating up and down in audible frequecy ranges. Clean cylinder head airflow is best I am told , flow bench remains quiet, only the vacuum cleaner motors whirring away.
How come cylinder head manufacturers never promote and publish cylinder head airflow speeds at 12, 28, 45, 65, inches of water vacuum depression? Seems to me it would be much more constructive and usefull when comparing cylinder heads and building an engine for street and stip drag useage.

Brian

 

[grumpyvette]

http://www.dartheads.com/tech-articles/port-volumes/


Tech Articles
Port Volumes

Posted on June 29th, 2011 under Tech Articles. Both comments and pings are currently closed.

Dart U Master

Port Volumes

By
David Vizard
By David Reher, Reher-Morrison Racing Engines

“The pressure curves explained what I’ve learned about racing engines through years of experience and observation.”

Unless your race car is powered by a jet engine or a turbine, a critical factor in engine performance is the pressure exerted on the pistons. The goal in race engine development is to maximize the cylinder pressure that pushes against the pistons and thereby rotates the crankshaft.

But have you ever thought about how that pressure is applied in the real world?

Several years ago, I had an opportunity to find out what actually happens inside a cylinder. We were working with GM on Pro Stock engine development, and an engineer showed up at our shop with a device to measure cylinder pressure inside a running engine.

As you would expect, a transducer that can survive the heat and strain of a Pro Stock big-block running at 10,000 rpm is a rather sophisticated (and expensive) piece of hardware. We modified a cylinder head to allow a sensor to be inserted into the combustion chamber, where it relayed data on cylinder pressure to a computer. The computer’s software then plotted a curve of cylinder pressure versus crankshaft position. What we saw was very instructive.

I expected that cylinder pressure would rise and fall smoothly as the fuel burned. What the transducer showed was very different: The pressure spiked upward to a sharp peak, and then dropped rapidly. When the fuel-air mixture ignited, the cylinder pressure rose in a nearly vertical line – and then it fell just as quickly. All of this happened within five or six degrees of crankshaft rotation. A big bang . . . and then nothing.

At this point I should point out the important difference between the actual cylinder pressure that we measured and the theoretical Brake Mean Effective Pressure (BMEP). BMEP is a calculation used by engineers and engine builders to compare the relative performance of different engines. It is the average (mean) pressure that would produce the engine’s measured output if the pressure on the pistons was uniform throughout the power stroke – which it obviously is not in the real world.

The engineer also had been testing a small-displacement turbocharged engine, and he shared its pressure graphs with me. The trace was strikingly different from our naturally aspirated engine. In the turbo engine, cylinder pressure rose relatively slowly, maintained a steady plateau for about 30 degrees of crankshaft rotation, and then fell gradually. The peak reading wasn’t as high as our naturally aspirated engine, but the duration was five or six times longer. In effect, the force of the cylinder pressure was pushing against the piston for a much longer interval. It’s no wonder that turbocharged and supercharged engines make so much power!

The pressure curves explained what I’ve learned about racing engines through years of firsthand experience and observation. We worked on a customer’s turbocharged, methanol-burning Toyota engine that produced 2058 horsepower from 189 cubic inches. For those of you keeping score, that’s almost 11 horsepower per cubic inch with a production block and cylinder! We filled the cast-iron block and aluminum head with high-pressure grout, machined billet main caps, and increased the diameter of the head studs to withstand the pressure that this engine was capable of producing.

Induction pressure definitely makes a difference. In a naturally aspirated engine, the force that fills the cylinders is the differential between atmospheric pressure (approximately 14.7 pounds per square inch at sea level) and the lower pressure inside the cylinders. When these pressures equalize, cylinder filling stops. Bolt a turbocharger (or supercharger) onto the engine and now there are three or four atmospheres of pressure in the induction system to fill the cylinders. In the example of the Toyota turbo engine, we had 60 psi pressure to ram air and fuel into the cylinders.

Even with sky-high cylinder pressure, the parts always looked perfect whenever we overhauled that engine. In fact, forced induction engines can be very durable, providing the components are designed to withstand the engine’s output and the fuel/air mixture and the spark timing are correct. The fact that there is always pressure in the cylinder, even during the overlap period when the intake and exhaust valves are open simultaneously, works as a cushion that keeps the piston/pin/rod assembly under constant compression. A normally aspirated engine can be harder on parts because the piston assembly is unloaded during the overlap period, allowing the rods to stretch and varying the loads on the pins and bearings.

I haven’t seen a cylinder pressure curve from a nitrous-injected Pro Mod motor, but I’m certain that the pressure spike is short and vicious. We typically set the spark timing in a nitrous Pro Mod motor at 5 or 6 degrees before Top Dead Center because nitrous oxide is such a powerful oxidizer that the fuel burns extremely fast, reducing the need for more than a few degrees of spark advance.

I’ve seen what the cylinder pressure in a nitrous-injected Pro Mod motor can do, and it’s amazing – flattened wrist pins and connecting rod bores knocked out of round. It takes some serious hardware to stand up to the forces in a Pro Mod engine. We’re not running Top Fuel parts yet, but we’re getting closer.

So whether an engine is competing in Bracket 5, Pro Stock, or Pro Mod, performance is ultimately all about cylinder pressure.

What you need to know to know and why to maximize your cylinder head investment.

Introduction:
We, at Dart, asked engine research consultant, university lecturer and world renowned performance tech author (over 4000 magazine articles and 32 books with #’s 33 and 34 in the making) David Vizard to write up for us the results of his port volume tests. Our goal here is to show that bigger is not always better. A fifty year veteran of high performance engine building and dyno testing plus a 4 figure number of race wins using his go fast technology puts David Vizard in a unique position to do this write up from firsthand experience. My suggestion is take the time to read it and reap the substantial benefits that this knowledge will impart.

- Jack McInnis
Dart Machine Ltd.

More airflow usually equates to greater output but in the case of a cylinder heads port sizing the lure of ‘bigger’ ports can be a trap waiting to snare the uninformed.

A 4 cycle engine is far from being a simple air pump. The principle reason turning apparent simplicity into real world complexity is the dynamic ‘stop – start’ nature of the flow through the engine and the fact that air is very much heavier than is often supposed. Rapidly changing rates of pressure and suction bring strongly into play both the momentum and the pressure wave effects that can be used to boost cylinder filling. At the end of the day this means that for a given displacement and rpm band there is a set of ports that are right for the job. Anything more than a few percent bigger or smaller is not. The following tests will demonstrate the difference delivered by a range of port sizes.

The Test Engine.

The test engine, a 383 Scat cranked stroker, is typical of the majority of small block Chevy’s built these days. Intended for use with 89 octane fuel this engine is well within the budget of most serious hot rodders.

This was one of my budget builds, a replica of which you can get at Pro Stock engine builder/racer Terry Walters in Roanoke VA. () for about $5400 turn key. The final price though will depend on the exact spec. For this test this Scat 3.75 inch stroker (budget cast steel series 9000 crank teamed with Scats budget 6 inch I beam pro-comp rod. Pistons were forged Silvolite ICON items. These in conjunction with the ‘as-cast’ 72 cc combustion chamber Dart heads tested delivered 9.8/1 CR. Had the 64 cc heads been use the CR would have been bumped to 10.7/1 for use with 93 octane. For what it is worth the torque and horsepower jump by about 15 numbers with the CR increase. For this engine the cam used was a custom 276 hydraulic roller grind done to precisely cater for the cylinder head characteristics, CR and displacement involved. If the saving of about $250 is of interest then it’s worth noting that a hot street hydraulic flat tappet cam with a 280 duration will deliver very comparable results. My book ‘How to Build Max Performance Small Block Chevy’s on a Budget’ (available http://www.Amazon.com) goes into very precise detail on the cam selection for a given combination. It goes so far as to give the cam for your build to a precision equal or better than testing a half dozen or more likely candidates on the dyno.

If you are into small block Chevy’s it’s worth noting that the reviews on Amazon.com indicate this to be the top rated book on the market. The info it contains is highly pertinent to not only the home engine builder but also the small shop that needs to build cost effective crate engines.

Headers used were a set of street Hookers with 1- 5/8 th primaries and a 2-1/2 secondary (collector) 18 inches long. The carb was a entry level 750 cfm AED unit mounted on a Dart two plane intake. It is worth mentioning here that it is, for this test to be valid, important for the intake manifold is capable of servicing the needs of the engine at both low and high speed. This means a manifold that flow well by virtue of with efficient ports not big ones. The Dart two plane item met those needs. At each cylinder head change, which ran small to large, the intake manifold was re- matched to the bigger ports at the manifold face. Ignition was via a Pertronix contactless unit. These are low cost and get the job done well.

The Test Heads.

Here is a shot of Darts Platinum heads chambers with and without valves. The design of these heads is the result of a lot of R&D on both wet and dry flow benches and the dyno. If this technology is to be converted into results on your motor it makes sense to choose the right port volume for the application.

The intent here is to run four pairs of the Dart Platinum Pro 1 heads having intake port volumes of 180, 200, 215, and 230 cc. Regardless of port volume all these heads flow about the same cfm until some 0.400 inches of valve lift have taken place (see Fig 1). Even at 0.600 were the test engines valve train tops out there are measurable flow differences. Because of these differences are the result of a port size increase they are a legitimate component in our bid to investigate the overall effect on the engines torque/power curve.

Fig 1. For all practical purposes there is no great flow difference between these heads until about the 0.400 lift mark. At this point the superiority of the bigger ports starts to pay off. Even so those differences are hardly significant until about 0.500 lift. To tap into the full potential of the bigger ports a valve lift of at least 0.600 was necessary.

Here are relative sizes at the manifold face of the 180 cc port runner (left) versus the 230 runner (right).

Check out the flow curves in Fig 1. and you will see that the majority of the flow increases with increasing port volume occurs at the higher lift value. So much so that any test that did not put enough lift into the valve to access the extra flow at high lift would be totally skewed in favor of the smaller port heads…

We talk port size in cc’c but the reality is that it is the port cross sectional area that is the factor we wish to control. So why is port cross sectional area important? If the area is bigger the flow surely goes up and that’s what we want is it not? Sure the engine wants as much airflow as possible but much of the flow through-put depends on port velocity and the generation of pressure pulses. This means an overly large port can hurt power even though it may, on the flow bench at least, flow better. The question is how does this work out on the dyno?

Dyno Results.

So you can better see what’s going on here the torque and hp graphs have been separated. The effect any particular head has on low speed output can be more clearly seen by considering the curves shown on the low end of the torque graph. To see the effects on the top end check out the curves from mid to high rpm on the hp graph.

Fig 2. The dyno results tell us that smaller, higher velocity ports, favor low speed output. (black 180, red 200, green 215, blue 230). These results also show that going too big (blue curve of 230 cc port) on the ports, for the intended combination produces, only marginally worse results almost everywhere in the lower rpm range, but what they ignore is theres a great many other factors at work here.

It is easier to see what is working best at the top end of the rpm range by looking at the hp curves. Here we see that the 215 cc port (green curve) equaled or beat the 230 cc port (blue curve) everywhere thus proving bigger is not always better. Combining what we see from the torque curves and the hp curves the 200 cc runner (red curve) proves to give the best average numbers over the rpm range tested.

Inspection of the torque curves in Fig 2 show the 180 cc ports (black) turned in the best numbers up to 3400 rpm with a peak of 482 lbs-ft. The 200 cc port (red ) though marginally lagging initially proved stronger from 3400 rpm up where it ran up with, or close too, the bigger ports.

Considering the torque curves of Fig 2 and the hp curves in Fig 3 shows that for our spec of 383 incher, the 200 cc ports delivered the best curve. The 215 cc (green curves) heads made the highest hp by pumping out 478 horses as apposed to 457 for the 180 cc runners, 472 for the 200 and 475 for the 230’s. The price the 215’s pay over the 200 to achieve this 7 hp advantage is that they give away up to 10 lbs-ft of torque in the rpm range from 2300 to 3200.

As for the 230 cc port runner heads these, on our 383, failed to deliver any advantage anywhere in the rpm range. The smaller 215 cc port heads actually outperformed the 230’s everywhere! If the test engine was capable of more rpm or was of a larger displacement the bigger port heads would have paid off.

So how do you decide what port volume your small block Chevy should have for best results? Check out the chart Fig 4. This will give a good starting point for port volume selection for a 23 degree headed small block Chevy. A word of caution here. Do not overestimate the power you are likely to see. All that will do is lead you into a bigger port than would be optimal. This leads to less power than you had hoped for. At the end of the day a little too small is better than a little too big!



A final point, just in case you are wondering, with a slightly bigger cam and 10.5/1 CR the as-cast 200 cc Platinum Darts, on this engine, allowed it to crank out 500 lbs-ft and a tad over 502 hp.

For more in-depth David Vizard tech on hi-performance engines and cylinder heads in particular go to http://www.motortecmagazine.net

David Vizard, considered by many to be one of the world’s leading Performance Auto Tech seminar speakers, will be holding a two day seminar on 10th and 11th Sept 2011 at TPI specialties in Chaska Minnesota. If you want to get the benefits of a seven figure dollar R& D budget for the cost of a seminar ticket this is the place to be. As a true performance enthusiast you about owe it to yourself to check out this seminar at http://www.davidvizardseminars.com.

 

[87vette81big]

What I have learned Grumpy is most available cylinder heads & induction systems in use are not the limitation
on C4 SBC & BBC C4 Corvettes.
Its the available Exhaust headers in $500-750 range.
You can't get Big tube 1-7/8"-2" primary & 3-1/2"- 4" collectors.
Easily bought for other cars.
Dana IRS holds back power level that can be planted the ground on laynch too.
Till both solved Mustangs will continue to set records.
Corvette guys will dream only.
Talking about well north of 600 HP.
High RPM'S OF 7-9K.

 

[87vette81big]

Have to remember recession never ended.
Obama care will kill nearly all budgets.

Available 4-link kits cost $5k in a C4 vette.
Custom headers $2k.
$7k.
More than most C4 vettes are worth today.

Home made only answer.

 

[grumpyvette]

theres at least a dozen guys who will debate endlessly about what intake, manifold or cam, is the best on most cars, a few will discuss headers, but darn few seem too understand that the exhaust scavenging , cam timing and intake runner design are all part of a matching system, and if any one parts not designed to operate at max efficiency , in the same rpm, displacement and flow rates its going to reduce the engines power potential.
as always an hour , or two spent testing and finding out the actual FACTS of the engines operation rather than making random guesses, and a bit of research into your options ,rather than guessing and buying parts before you have verified the problem goes a very long way toward preventing you from wasting money and time!
what amazed me for years was that so many guys I talk with have NEVER even ONCE measured the engine in their cars EXHAUST back pressure, at wide open throttle so they have ZERO idea if they are dealing with an exhaust on the car that's hurting the engines power potential
and I doubt that number exceeds 10% of the guys I talk with , and of those few darn few guys ever do the math to design a better exhaust or do much more than complain about the lack of off the shelf options to cure the problem ...if ..IF they even understand it MIGHT BE an issue limiting the cars performance
if you select a cam thats designed to maximize power at lets say 6000rpm in a 12.5:1 compression 454, you need to select heads, intake, and an exhaust system that is designed to operate efficiently at the same rpm and power band.

one reason a properly port matched tunnel ram intake flows efficiently is a strait path to the intake valve, in the cylinder head from the plenum, match that to a well designed exhaust , high compression and matching cam timing,and you can significantly increase an engines ability to breath

READING THESE THREADS MAY HELP GUYS READING THIS



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.circletrack.com/enginetech/1 ... ch_engine/
calculate horse power from intake port flow rates
http://www.wallaceracing.com/calcafhp.php

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

http://www.wallaceracing.com/ca-calc.php

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

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

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

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

http://www.wallaceracing.com/area-under-curve.php

http://www.wallaceracing.com/piston-speed-velocity.php

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

 

[grumpyvette]

http://www.airflowresearch.com/articles ... arison.php

 

[Grumpy]

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

Hey everyone im new to the site so please forgive me if im doing this wrong or in the wrong place. First I want to mention the reasons for the way our engine is built. In the class we race in we are chipped at 6500 rpm, limited to .500 lift measured at the valves, must run oem cast iron heads, and run a holly 4412 2 barrel with a restrictor plate under it. We are limited to 370 CID. Our engine is a 350 .030 over (355) with vortec 062 .194 heads. Roller Rockers. 5.7 rods with an aftermarket stock crank. flat top pistons. I am wondering if anyone can tell me at which point in the rpm range I am making peak torque without me putting this thing on a dyno. Cam is a howards mechanical flat tappet cam with a lift of .515 I and .515 E advertised. Degree of duration at .050" is 252 intake and 258 exhaust. Lobe center is 106 and intake c/l is 102 advertised. Looking to correctly select a torque converter. Truck weighs approx. 4300 lbs and races in short course off road. We currently run a 3800 stall converter and tranny temp hasn't gotten over 185 so we have plenty of room to play with there. What does everyone think and what other info to you need?? thanks a bunch

A useful tool for calculating the power potential of cylinder heads is the following formula HP=. 257 x (peak) airflow x number of cylinders. If we plug in flow data from a CNC-ported small-block cylinder head that offered a peak flow of 304 cfm, we get the following: HP=. 257 x 304 x 8 or 625 hp.
you may find these calculators rather useful, but I think your current converter stall speed is pretty close to ideal in that application, with that displacement that cam and those heads your power band more than likely falls in the 4000rpm-5800rpm band

engine
http://www.wallaceracing.com/max-rpm.php

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

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

http://www.wallaceracing.com/curtain-area-calc.php

http://www.wallaceracing.com/max-rpm2.php

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

drive train

http://www.wallaceracing.com/calc-gear-tire-rpm-mph.php

http://www.wallaceracing.com/calc-rgr.php

 

[87vette81big]

I will take the smaller port heads on the street myself Grumpy.

Off topic kinda, I watched a 1974 Pontiac Lemans sell on ebay recent.
Car was in bad shape. A beater Rat Rod.
But it had a real nice 455 .
Edelbrock Aluminium heads.
Guy said it was real fast. Won every race on the street local. Perhaps he did.
Every Pontiac guy watches ebay along with Mopar guys like my bud Bob nearby.
I thought the car would sell for at least $7,000 just for the engine & built Turbo 400 Trans.
To my disbelief it sold for just $3,000.00.
Guy said he had $18,000 in the engine.
It was a 455 Stroker. 474 ci.

I am not the only that likes factory Iron performance Poncho heads .

 

[Strictly Attitude]

I will take the smaller port heads on the street myself Grumpy.

Off topic kinda, I watched a 1974 Pontiac Lemans sell on ebay recent.
Car was in bad shape. A beater Rat Rod.
But it had a real nice 455 .
Edelbrock Aluminium heads.
Guy said it was real fast. Won every race on the street local. Perhaps he did.
Every Pontiac guy watches ebay along with Mopar guys like my bud Bob nearby.
I thought the car would sell for at least $7,000 just for the engine & built Turbo 400 Trans.
To my disbelief it sold for just $3,000.00.
Guy said he had $18,000 in the engine.
It was a 455 Stroker. 474 ci.

I am not the only that likes factory Iron performance Poncho heads .

No you are not every time I find poncho or olds it is a stripped down short block

 

[87vette81big]

No you are not every time I find poncho or olds it is a stripped down short block

Some of the best advice I ever got from Grumpy is that a Good Fullsize Truck 4X4 & a Good Dual Axle car trailer is a must have.
The good deals are always a distance away.
Must have a way to get Engines, TH400's & My Poncho 9.3's rear diffs home.

 

[Grumpy]

like I stated many times,
its the combo of the engines,
compression,
displacement ,
cam timing
and the exhaust scavenging ,
and the intake manifold design,
NOT the intake port cross sectional area,
that are the most critical factors, in the engines lower rpm and mid rpm torque.
but for damn sure an intake runner port can be small enough to noticeably restrict upper mid range and peak power significantly,

 

[DorianL]

Yes that first video has gone viral. I had seen it an it made me raise an eyebrow.

However, it does seem to mean that I would be extremely happy with a mild-cam 383 with 195cc heads. I don't need to go crazy on this one to make it a fun drive for both the wife and me.

 

[Grumpy]

For 5 decades I've heard endlessly about how installing larger free flowing cylinder heads would devastate the engines ability to make any low or mid rpm torque.
especially when Id suggest using a set of smaller 300cc-320cc, aluminum,rectangle port heads on a 496 BBC, or 200 cc-210cc heads on a 406 sbc, I was asked to build
yet on every engine I've ever had built or had some guy ask me to look at, to see why it ran a great deal less impressively than he expected it too,
they brought into my shop its was very obvious (at least to me) that it was the combo of low compression, too little displacement, with too much cam duration ,
a restrictive exhaust or some guy who was trying to save money and continuing to use a stock stall speed torque converter, or retain a badly mis-matched 2.87:1-3.08:1 rear gear ratio,
with an engine that he miss matched components by slapping a large carburetor , and a single plane intake on,an engine that will rarely exceed 6000 rpm, that was the major reason.
if you want an engine combo to run your first step is to logically match the list of components you,ll use to the application,
and that requires you stop, engage the brain and think things through carefully,
and the most common way to screw up the process is to over cam a low compression engine,
have a restrictive exhaust or mis-match the drive train gearing to the engines power band.
I'm not a big time commercial engine builder, but I've built well in excess of 150 plus engines over the last 50 years, (3-5 a year on average)
the issue with using a lot more cam duration , is simply you need the cam duration to match the static compression too allow the engine resulting dynamic compression,
too maximize the engines effective compression but keep it just under the detonation threshold limits for the octane of fuel used.
change the compression and cam duration and you change the power band and where in that power band the effective exhaust scavenging will work best.
A useful tool for calculating the power potential of cylinder heads is the following formula HP=. 257 x (peak) airflow x number of cylinders. If we plug in flow data from a CNC-ported small-block cylinder head that offered a peak flow of 304 cfm, we get the following: HP=. 257 x 304 x 8 or 625 hp.

if your experiencing detonation issues that are cured by swapping to higher octane rated fuel, and you would prefer to use the lower octane , less expensive fuel, you should adjust your cars ignition advance combination , so that its advance curve has either less initial timing, or delaying the mechanical advance vs. rpm with some stiffer springs, or a combination of both might reduce the pinging under load at 2500-3500 rpm where its most commonly seen,. Does this detonation or pinging, only occur at WOT? If not, limiting the vacuum advance with a stop, or using an adjustable vacuum advance unit and raising the amount of vacuum required vs. the amount of vacuum advance might be warranted also and installing a lower temp rated t-stat and adjusting the engine fuel/air ratio a bit richer may also help..
notice they kept the same cam duration and compression ratio in the video,
thus the torque curve remained rather consistent and only the slightly different intake port velocity changed.
as long as the timing and fuel/air ratio remained constant and the exhaust scavenging and cylinder fill rates remained consistent the power produced stayed rather consistent,
as the ports cross sectional area increased
,power on the upper rpm range increased due too,
a less restrictive port not choking off the upper rpm cylinder fill efficiency.
but the larger ports had little effect on the lower and mid rpm ranges
there will be guys suggesting that the larger port size requires a longer duration cam to breath efficiently....
while thats certainly correct the fact is that the longer duration cam timing ,
would also require a higher matching static compression , and a change in drive train gearing to work correctly.. in a car, as the engines whole power band would move higher,in the rpm range,
a point all too often being
ignored in the dyno tests and discussions you see, posted

a close look at the simple mechanical physics of engine component timing will show you that as cam duration is increased the intake valve close point in relation to the crank assembly rotation, and as a result the upward movement of the piston,
in the cylinder on the compression stroke in relation too,
the intake valve seating and sealing the cylinder,
so that upward moving piston can compress the trapped fuel/air mix above it,
into the combustion chamber will occur later ,
(remember nothing gets compressed until both valves seat and seal)
and thus the volume of trapped fuel/air mix is reduced at lower rpms, with a longer duration cam timing.
if you reduce the effective mass of compressed fuel/air mix,
you reduce the potential pressure in that cylinder on the power stroke.
as the rpms INCREASE ,this loss of fuel/air mix trapped above the piston is partially offset,
by increased cylinder fill efficiency rates as inertial ram tuning and more effective exhaust scavenging,both increase as rpms increase if the proper compression and cam timing are well matched.
both factors tend to increase the mass of trapped fuel/air mix that gets compressed by the raising piston on the compression stroke.
the longer duration cam and overlap in valve timing, allows the , much more efficient properly timed exhaust ,
scavenging to draw in the intake fuel air mass and draw out the exhaust gases.

I've found BRODIX I.K. heads are very good quality, and decent value per dollar,
for a high performance street/strip style engine
https://craftperformanceengines.com...nder-Heads--brodix_cylinder_heads_sbc_ik.html

trickflow 230cc makes a good racing sbc head choice

https://www.trickflow.com/parts/tfs-3241t001-c03

profiler 210cc is a good compromise race and street strip head
https://www.profilerperformance.com/176-sbc-23-degree-heads.html

https://www.summitracing.com/parts/afr-1055/overview/make/chevrolet
http://www.airflowresearch.com/210cc-sbc-race-cylinder-head/

related info
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

https://www.profilerperformance.com/176-sbc-23-degree-heads.html

http://garage.grumpysperformance.co...olishing-combustion-chambers.2630/#post-48319

http://garage.grumpysperformance.co...r-flow-heads-the-best-choice.9415/#post-34274

http://garage.grumpysperformance.co...good-street-combo-your-after.5078/#post-14433

http://garage.grumpysperformance.com/index.php?threads/more-port-flow-related-info.322/#post-722

http://www.superchevy.com/how-to/en...-0902-chevy-engine-port-variations-measuring/
http://www.hotrod.com/articles/choosing-the-right-camshaft/
http://garage.grumpysperformance.com/index.php?threads/bits-of-383-info.38/

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

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

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

http://www.wallaceracing.com/calc-cfm-head.php

http://www.wallaceracing.com/ca-calc.php

http://www.wallaceracing.com/csa-calc.php

http://www.wallaceracing.com/area-under-curve.php

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

http://www.wallaceracing.com/throttle-blade-diameter.php

http://garage.grumpysperformance.co...mble-and-swirl-quench-squish.4081/#post-12283

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

http://garage.grumpysperformance.com/index.php?threads/port-speeds-and-area.333/

http://garage.grumpysperformance.com/index.php?threads/valve-seat-angles-and-air-flow.8460/

http://garage.grumpysperformance.com/index.php?threads/header-dimension-calculator.15013/

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

http://garage.grumpysperformance.co...-by-step-guide-with-pictures.5378/#post-73427

http://garage.grumpysperformance.co...llecting-cylinder-heads.796/page-2#post-90819

http://garage.grumpysperformance.co...ng-combustion-chambers.2630/page-3#post-77963

http://garage.grumpysperformance.com/index.php?threads/the-new-215cc-vortec-heads.266/#post-75012

https://www.enginebuildermag.com/2006/11/wet-flow-testing/

https://rehermorrison.com/tech-talk-40-wet-flow-revelations-the-monsoon-inside-your-motor/

https://www.musclecardiy.com/cylinder-heads/the-basics-of-wet-flow-cylinder-head-testing-part-4/

http://garage.grumpysperformance.co...ir-ratios-that-gets-ignored.15506/#post-95741

https://www.airflowresearch.com/wet-flow-development/

https://www.hotrod.com/articles/cylinder-head-flow-bench/

https://www.chevydiy.com/airflow-basics-for-chevy-small-block-cylinder-heads/

http://www.superchevy.com/how-to/engines-drivetrain/sucp-0803-performance-cylinder-head-comparison

http://garage.grumpysperformance.com/index.php?threads/port-speeds-and-area.333/#post-72826

SBC Cylinder Head Info

http://enginebuilderprofessional.com/chevy_flow_data.pdf

Quench: Unlocking Performance Squished Between the Piston and Head

Quench is the clearance between the piston and cylinder head at TDC. It can affect engine effeciency and performance, if you truly understand it.

www.enginelabs.com

Stan Weiss' - Cylinder Head Flow Data at 28 Inches of Water -- DFW / FLW Flow Files for use with Engine Simulation Software

Cylinder Head Flow Data @ 28 Inches of Water -- DFW / FLW Flow Files for use with Engine Simulation Software

users.erols.com

 

[Grumpy]

port speeds and area

I CAN,T EVEN TELL YOU HOW INSANE SOME CONVERSATIONS I HAVE SEEN GUYS GET EVOLVED IN ARE! GUYS TELL YOU A 210CC air flow research HEADS GOING TO ABSOLUTELY KILL Torque ON A 383 BUT ITS FINE FOR A 400 SBC, WHAT TOTAL b.s, your cylinder heads port size needs to be selected with both displacement...

garage.grumpysperformance.com