Air Velocity Speed Limit: Max Velocity Heads + Tuned Intake = Turbulence?

NewbVetteGuy

Well-Known Member
Here's a question I've been pondering; it has 2 constituent parts/ ideas that come together to make the question possible so bear with me:

1. Modern SBC "Street" heads like the AFRs and Profilers have been laser-focused on keeping air speeds up and maximizing airflow velocity to improve torque and cylinder filling across the range. Darin Morgan has gone so far as to say that this type of head is "velocity limited" (they're trying to keep the air speed close to the max at which you no longer can make more power and the airflow goes turbulent- so when you start to spin up in RPMs the airspeed gets too high and flow goes turbulent and you don't flow more air and you don't make more power.) -We can see this from the airflow in these head's falling off at high lifts and power falling off even with high speed capable valve trains at high RPMS.


2. Tuned intakes use pressure wave reflections to jam more air into the cylinder in certain narrow RPM ranges; this increases air velocity through the intake path, within this RPM band.


Question: Will a combo that utilizes a modern SBC "max velocity" street head and a tuned intake hit the max power velocity "wall" much faster than a combo that utilizes a normal single or dual plane intake? (and cease to make power at a lower RPM, limiting max HP)

Specific applied example of my question: If your build uses an AFR 180 head or a Profiler 185cc head, that would normally not go turbulent until 6,500 RPM, would a tuned intake that further increases air velocity cause you to hit the "speed limit" at a lower RPM and prevent you from reaching your max power RPM sooner? -Causing your power curve to drop off sooner- not because of valve train issues or lifter bleed down but simply because your max air speed went too high?

(My guess is that the solution would be to pull out PipeMax and to figure out how much you need to port your heads/ increase your heads' CSA at the pinch point to prevent the flow from going too fast until after your desired peak power RPM...) -My other thought on a solution would be to go with one size bigger head if PipeMax calculations are estimating your air velocity to go above the max velocity limit.





Anyone have any dyno charts from say an AFR 180cc head or Profiler 185cc head on a 350 or 383 with a high RPM-capable valve train and something like a Holley Stealth Ram?

-(IF anyone's got them, please post them here if you can so we can all look together.)


Adam
 
And before anyone goes there, yes I understand that VELOCITY is more important than total airflow. This is why I don't like the idea of going up one size on the heads' intake size and my preferred solution would be small modifications in the CSA at the choke point to keep velocity as high as possible while still hitting the target peak HP RPM.
 
I ran afr 195 street eliminators with a full race isky circle track cam and an rpm airgap it would pull hard and fast through the rpm range it really woke up at 4000rpm and pulled really hard I was short shifting it cause I did not know my bottom end specs just my pistons and compression on that engine.
 
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
an engines Torque peak is almost always very closely related to the point in the rpm curve where the most effective/efficient cylinder fill, cylinder fill is related to both intake port cross sectional area and exhaust scavenging,efficiency, and is limited by port stall, and cam duration in relation to displacement, compression and valve train stability, ...all factors are easily calculated
links below
Cylinderspressure.png


Cylinder-Pressure-Graph.jpg



volumetric.gif


useful RELATED INFO you might want to read

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

http://www.pontiacracing.net/js_header_length1.htm

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

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

http://garage.grumpysperformance.com/index.php?threads/calculating-ideal-port-size.624/

http://garage.grumpysperformance.com/index.php?threads/sellecting-cylinder-heads.796/

http://garage.grumpysperformance.co...ting-a-port-size-and-intake-for-nitrous.4930/

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

http://garage.grumpysperformance.com/index.php?threads/calculating-header-design.185/



EXFLOWZ4.jpg

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

portcsa.jpg

portvl.png

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/
porting+valve_area.jpg

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


FlatVsRollerChart.gif

LiftCurveAread.gif


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)

HeadsVsPortFlow.JPG



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

http://garage.grumpysperformance.co...ing-parts-and-a-logical-plan.7722/#post-51341

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

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

http://garage.grumpysperformance.com/index.php?threads/more-port-flow-related-info.322/#post-12391

http://garage.grumpysperformance.co...at-angles-and-air-flow.8460/page-2#post-32923

http://garage.grumpysperformance.co...olishing-combustion-chambers.2630/#post-50247

http://garage.grumpysperformance.co...-calculators-and-basic-math.10705/#post-46737

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

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

http://garage.grumpysperformance.co...city-vs-intake-runner-sizing.1099/#post-26215

http://garage.grumpysperformance.co...-head-will-bigger-ports-help.7463/#post-25269

http://garage.grumpysperformance.com/index.php?threads/porting-can-help.462/page-2#post-24466

http://garage.grumpysperformance.co...-your-compression-torque-dcr.1070/#post-20586
 
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That a lot of info and it's all already posted here; I'm having a difficult time trying to see how to apply any of it to my question, though.

I have not only the cross-sectional area of my intake 1.75", but the end-to-end centerline of the runner length from the intake all the way to the valve: 19.25".


I've also got CFM flow #'s and MEASURED velocity #'s at the valve curtain and throat of a set of Profiler 195ccs that have only had VERY minor porting by Chad Spier racing if any of this helps to calculate / estimate the air velocity at a given RPM with the head/ intake combo...

I'm just not sure on what's required to "solve" for the air velocity of a given combo at a given RPM...


Adam
 
the idea of the posted linked info was to ideally allow you to look up and find out WHY and HOW you select a certain matched combo, but heres the basic info
(yes theres more but Ill leave you a few minor points on valve size, seat angles plenum volume,cam duration, and exhaust header config. to still find

http://www.wallaceracing.com/chokepoint.php
http://www.rbracing-rsr.com/runnertorquecalc.html
http://www.velocity-of-sound.com/velocity_of_sound/calculator1.htm
http://www.wallaceracing.com/header_length.php
cosp3.jpg

Your PORT STALL,RPM computed from your Cross Sectional Area of 1.75 and Bore of 4.03 and Stroke of 3.75 is 4,997 RPM

3.1 sq inches is about ideal, on a serious race engine with 383 cubic inch displacement, if max hp is the goal, as it puts the max torque near 5700 rpm and peak hp at about where max piston speed is becoming critical with good quality components and a solid lifter cam, obviously you can use the calculated input's to change the results to match changes in your intended goals, the linked info contains FAR more related tips
if your building a 383 with smaller ports like that you'll have a very torquey
mid rpm range combo, but sacrifice peak power
your current port length of 19.25 puts the ram tune at 3700 rpm with a 1.75" cross section

FlatVsRollerChart.gif

as the cam duration increases the valves tend to close later in relation to piston movement up the cylinder ion the compression stroke, so your effectively trading more individual cylinder volume , with a low duration cam for a bit less trapped cylinder volume BUT more power strokes per second with a longer duration cam that allows the engine to make better power at a higher average rpm range
postiongraph.jpg

http://garage.grumpysperformance.co...alves-and-polishing-combustion-chambers.2630/
http://garage.grumpysperformance.com/index.php?threads/bits-of-383-info.38/
http://garage.grumpysperformance.com/index.php?threads/semi-fool-proof-cam-sellection.82/
 
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Grumpy, I have a question, I ran across this add.
for the new LS chevy heads, notice the ports are 260cc,
and I noticed the .700 lift was 384 CFM at .700 lift
well thats well above most SBC flow numbers in fact its decent for most BBC cylinder heads
yet the port size is only 260cc which is about the port volume of a stock,
muscle car era, oval port BBC cylinder heads intake port


260cc LS3 Cylinder Head
LS3_Intake_Recolor__86161.1493677807.500.290.png

http://www.airflowresearch.com/260cc-ls3-cylinder-head/
260cc Street Head Flow Chart
.200 .300 .400 .500 .600 .650 .700
Int 159 234 293 336 366 377 384
Exh 112 158 207 235 248 251 255


Heres a small rectangular port BBC AFR head with similar flow numbers,
notice its a 315CC intake port,
so why does the BBC cylinder head need a port,
thats roughly 55cc larger to flow similar air flow or put a different way,
why can't a small oval port BBC head flow similar numbers.

315cc BBC Rectangle Port Cylinder Head
http://www.airflowresearch.com/315cc-bbc-rectangle-port-cylinder-head/
CNC_Intake__24045.1449253177.500.290.png

315cc BBC
.200 .300 .400 .500 .600 .700 .800
Int 169 249 312 353 380 386 387
Exh 146 184 238 271 296 310 315

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
brodixik.png


trickflow 230cc makes a good racing sbc head choice
trickflow230.png

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

176-210cc.png




https://www.summitracing.com/parts/afr-1055/overview/make/chevrolet
http://www.airflowresearch.com/210cc-sbc-race-cylinder-head/
afr210cc.png



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
119651.png

119651.jpg

119651.jpg



251.gif

well the first thing Id point out is the volume of any engines cylinder heads intake port is restricted or limited, by the length, width and distance from the cylinder heads intake manifolds mounting surface to the back of the intake valve and that distance varies a great deal between different engine designs.
you can,t randomly compare two totally different engine designs,
and get comparable port volumes.

it should be rather obvious that a port thats taller & narrower or shorter in length will result in less internal volume,and if the line of sight from the intake manifold mount surface to the valve is both shorter and straighter it might flow air with less potential flow restriction.
the engineers that designed the chevy LS series engine did not consider any interchangeability between the two totally different engine designs , the LS series engine was designed at least 35 years after the BBC engines and they took advantage of computers and research that was done in that 35 plus years to improve the basic design, but keep in mind the BBC while an older design, it still has the advantage in the basic design allows a significantly larger displacement
the LS series is basically designed to be a 327-454 displacement engine
the big block chevy is a 366-632 displacement capable design.
yes both engines can be built larger with after market components
portcsa.jpg

https://www.calculatorsoup.com/calculators/geometry-solids/rectangularprism.php


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

a great deal of the info you may want can be calculated after carefully measuring the intake port and runner length and cross sectional areas.(remember its not the intake port gasket cross sectional opening, cross sectional area, its the smallest part of the port cross sectional area and valve throat areas that limit port flow rates)
if as an example we selected a port with about a 2 sq inch cross sectional area, you'll find max torque on a 350 will fall near 4000-rpm and port stall near 6000-rpm

rtyu1.jpg

rtyu2.jpg

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

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

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


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

http://www.rbracing-rsr.com/runnertorquecalc.html
13cal.jpg

17903.jpg

ticalcx1.jpg

http://www.walmart.com/ip/Texas-Instruments-TI-30X-IIS-Scientific-Calculator/1535939
http://www.summitracing.com/parts/cca-5605/overview/
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
pencilbal.jpg

watch the video, and 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,
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.

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

I know yes I'VE also done this, that's how we ALL gain experience....
I find it really amazing how often I see guys get 1/2 way into an engine assembly process and they suddenly want to change or modify some major component,
now in most cases that get expensive and the change will result in having to make corresponding matching changes in other
components
you could have saved a great deal of time and money,
by taking extra time in the research, phase of the engine build,
by simply shopping carefully,for each component and calculating how it will match the other selected components and it generally helps if you deal with a well known major name brand manufacturer and ask lots of carefully thought out questions and know exactly what your trying to accomplish and what your options are that you would want or prefer to have, especially in major components like the rotating assembly, and valve train components ,
ordering custom made 2618 forged aluminum, pistons with,
light weight tool steel wrist pins,
gas ports,
and thermal coated domes,
and friction reducing skirts,
a BALANCED 4340 forged steel rotating assembly,
with connecting rods that use ARP 7/16" rod bolts of the correct for the application strength rating.


Piston Alloy Comparison
4032........................... ................................2618
High silicon ......................................... ...........No silicon
Low expansion ................................... .........High expansion
Tighter piston-to-wall clearance . ...........More Piston-to-wall clearance needed
Quiet Operation .................................Noise when cold
Less ductile ........................................... More ductile
More stable & consistent.................... ...... Higher resistance to detonation
Longer life cycle.............................................. Shorter life cycles
Harder .................................................... ........Softer

http://www.venolia.com/


RELATED LINKED INFO
http://garage.grumpysperformance.com/index.php?threads/snap-ring-pliers.11029/#post-48839

http://garage.grumpysperformance.com/index.php?threads/precision-measuring-tools.1390/

http://garage.grumpysperformance.com/index.php?threads/piston-suppliers.2208/#post-19329


http://garage.grumpysperformance.com/index.php?threads/thermal-coatings.2610/#post-12861

http://garage.grumpysperformance.com/index.php?threads/piston-related-info.110/#post-31943

http://garage.grumpysperformance.com/index.php?threads/types-of-crankshaft-steel.204/#post-240

http://garage.grumpysperformance.co...ore-clearance-on-your-block.14251/#post-72471

http://garage.grumpysperformance.co...lling-connecting-rods-pistons.247/#post-57737

http://garage.grumpysperformance.co...y-in-building-a-good-engine.11682/#post-54682

http://garage.grumpysperformance.co...a-scat-rotating-assembly-be.11495/#post-52962

http://garage.grumpysperformance.co...-calculators-and-basic-math.10705/#post-46582

http://garage.grumpysperformance.com/index.php?threads/rod-bolts-rpm-vs-stress.341/#post-68856

http://garage.grumpysperformance.com/index.php?threads/rotating-assembly-bearings.9527/#post-70329

http://garage.grumpysperformance.com/index.php?threads/piston-to-bore-clearance.4630/#post-12417

http://garage.grumpysperformance.co...n-you-plan-for-quench.11298/page-2#post-51613

http://garage.grumpysperformance.co...-displacement-street-engine.10961/#post-48185

http://garage.grumpysperformance.com/index.php?threads/piston-coating-deburring.4516/#post-16279

http://garage.grumpysperformance.com/index.php?threads/engine-balancing.3900/#post-10338

http://garage.grumpysperformance.co...ns-one-really-over-looked-part.978/#post-1711



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/
 
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