[Steve C.]

http://www.wallaceracing.com/chokepoint-rpm.php
Calculator for cross section based on rpm

Fun to play with numbers...

A truck motor 4.180 bore 4.210 stroke at 5000 rpm = 2.33 sq inches.
Use a factory 2.05 x 1.30 intake gasket at 2.31 sq inches.
Same bore & stroke taken to 6000 rpm, needs 2.596 sq inches or a Felpro 1233 gasket at 1.180 x 2.200 or 2.596 sq inches.
A truck motor 505 at 6000 rpm needs a SCE #128103 gasket, 2.320" tall.

[johnta1]

Here's an interesting discussion.
Speedtalk

[John Bailey (GTOKID)]

I FEEL DUMBER FOR ACTULLY READING THIS POST. 6X 455 CAST ROD,TRW'S ,USED ROLLER, HERBERT LIFTERS,VICTOR, 1050 CARB, 3.90, 74 GTO 3555LBS 10.27 @ 127 UNLEADED GAS....BIG DEAL NOT!!! ITS MORE THAN HEADS AND CAM....ITS THE WHOLE COMBO. GUYS LIKE HAND,OWENS, HOSTLER WORK ON THE WHOLE CAR. YOU DO NOT NEED ALU HEADS TO GO FAST

[uneasyrider]

Theoretical cfm (total for engine) = (rpm x cid)/3456
Q (flow rate in cfm) = V (velocity in ft/min) x A (area of the inlet/port/carb in sqft.)
piston velocity(V) = (stroke(in) x rpm)/6

Q=(6000x462)/3456=802.1cfm total thus div. by 8 for ea. cyl.=100.3ft^3/min
V=(4.21x6000)/6=4210ft/min
100.3ft^3/min=4210ft/min x A
A=0.0237ft^2=3.40in^2

3.40 is about 23% larger than the 2.6(2.596) the formula gives. They must be adding in all the other things in there some place or I've screwed up which wouldn't be the first time.

[uneasyrider]

Originally Posted by Steve C.

http://www.wallaceracing.com/chokepoint-rpm.php
Calculator for cross section based on rpm

Fun to play with numbers...

A truck motor 4.180 bore 4.210 stroke at 5000 rpm = 2.33 sq inches.
Use a factory 2.05 x 1.30 intake gasket at 2.31 sq inches.
Same bore & stroke taken to 6000 rpm, Felpro 1233 gasket at 1.180 x 2.200 or 2.596 sq inches.
A truck motor 505 at 6000 rpm, SCE #128103 gasket, 2.320" tall.

That works out a lot better than what I was comeing up with. My calc. was about 23% bigger than the real world. They must be accounting for the tuning effects of the manifold(s) and cam etc. The overlap, scavenging from the exhaust and the "ram tuning" of the manifold would increase the velocity and density of the charge. OR I screwed up somewhere and that wouldn't surprise me.

[Skip Fix]

I think what your previous post and the caluclator shows is there are ALOT of different formulas for the rpm range based on CSAs, choke points, cc of port, cc of entire intake tract, etc etc. They ALL are just ball park estimates and real world combinations have alot more factors in them.

It is the reason why 3 different heads from the same manufacturer, same port length, same cc, probably the same CSA, same intake, cam,carb can have 3 different rpm ranges! SHAPE!

[slowbird]

I know that Steve knows this but two things about his cross section. One the min. doesnt occur at the gasket but at the pushrod area, two you need to factor in the corner radius, usually that is about .05 to .100 subtracted off. I believe that a stock Pontiac head is around 2.00 at the pushrod area, which is about 4800rpm

[Steve C.]

The program mentions choke point. That one and many similar calculators we play with do show a trend as the inputs are varied, that can be very helpful.

One good way to illistrate the point about runner shape. Within the Performance Trends program there is a area to input port dimensions and it calculates the runner volume. Input 1.2 x 2.3 x 5.125 with a retangular port shape and it suggests 231 cc runner, change the input to reflect a rounded retangular shape and it drops to 219 cc's.

[60man]

Originally Posted by GTOKID

I FEEL DUMBER FOR ACTULLY READING THIS POST. 6X 455 CAST ROD,TRW'S ,USED ROLLER, HERBERT LIFTERS,VICTOR, 1050 CARB, 3.90, 74 GTO 3555LBS 10.27 @ 127 UNLEADED GAS....BIG DEAL NOT!!! ITS MORE THAN HEADS AND CAM....ITS THE WHOLE COMBO. GUYS LIKE HAND,OWENS, HOSTLER WORK ON THE WHOLE CAR. YOU DO NOT NEED ALU HEADS TO GO FAST

Agreed...it's the whole package working together that makes are car what it is. I followed Jim Hands policy when building my car from scratch..My car is more of a race only deal now but with last 462 "race motor" Jim's wagon could run a little faster than mine and go on road trips....with 3.36 gears !! Different strokes for different folks..
Not that heads aren't important but they are only a part of the equation..IMO
I saw a set of SBC heads at a shop a while back that flowed 440 CFM !!
The port entry was only 2/3rd the size of mine...but the bolws were like pint milk cartons ...of course there was no mention of velocity ..SBC so I assume 9-10K + power band..

[Geoff]

I just received my 65cc KRE D port heads; they are unported. The intake openings at the flange are quite small, but the bowls look huge compared to a stock D port.

[uneasyrider]

Boy the site is sure messed up. I posted that twice becuase the first time I didn't think any of it went through.

Anyway, I agree, they are all "ball park" figures but I think that calculator is closer than what I was doing.

[Rocky Rotella]

60man, it's great seeing the old cars run so well! I love that launch photo! What'd you do to the suspension to drop 60' times to 1.50 and yank the front tire? Are you running an auto or manual?

Keeping with the theme of the topic, what heads are you running? Do you know the peak airflow and port volume. Also what is the cam lift and duration, and engine shift point?

Keep up the great work, I want to see your Ventura run sometime!

[60man]

Originally Posted by Rocky Rotella

60man, it's great seeing the old cars run so well! I love that launch photo! What'd you do to the suspension to drop 60' times to 1.50 and yank the front tire? Are you running an auto or manual?

Keeping with the theme of the topic, what heads are you running? Do you know the peak airflow and port volume. Also what is the cam lift and duration, and engine shift point?

Keep up the great work, I want to see your Ventura run sometime!

Thanks Rocky..off topic for a minute..Tom Molyneaux took that picture at Cecuil County last season. He is a free lance photographer/writer. Do you know him ?? He to was surprised !! It has pulled bigger wheelies !! The suspension is basically "stock". I just added some Comp. Eng. shocks all around and run Hoosier radial slicks. They are only 9" to boot I run a TH400 with a 4,600 stall converter and motor was built for TORQUE !! I don't know what the port volume is but I do know they flow right at 310 CFM ..KRE D ports. When I discussed buying these head with Jeff K. I asked to retain good velocity as well as CFM..Not sure what he did but I am pleased. Went from 12.19 to 11.68 off the trailer....Cam is a relatively "small". UD solid.
It's 247/259 @ .050 and 110 LSA/degreed in at 106..lift is .580/.610 with HS1.65's..I shift the motor at 5,600-5,800..and generally launch off idle to hit tires hard to make them bite.
I'll have to check into the port volume as it applies to this subject. I might add I was running ported 670's and a slightly smaller Hyd. cam and running the 12.19's..
I have followed and applied a lot of Jim Hand's ideas for my Land Barge...it worked !! Not sure if I'll make the Hot Rod Reunion this year. Maybe you can see car at Norwalk...I've read a lot of your articles. Keep up your good work ...