How much CSA will be ideal

[68corvette]

CFM is needed to calculate coefficient of discharge, which can be used to calculate how much pressure differential the head is able to see in a running engine.
Pressure differential can be then used to calculate the actual flow speed and maximum potential volumetric efficiency.

So CFM is not irrelevant, but not nearly as important as some from marketin department want to make people believe.

[Erland Cox]

I have never seen a big port hurt torque and hp.
But this is on 4 cylinder engines where I can adjust the runner length for bet hp and totque.
I think that you are wave tuning the engine with port velocity on a single 4 barrel V8 engine.
A smaller CSA makes the wave travel back and forth slower so the engine tunes as if the port was longer.
With a bigger port it takes less time for the wave to arrive back to the valve so the engine can tune at to high rpm.
Intake valve open waves.

Erland

[DrillDawg]

Back around 1980, RM pro stock big sbc made 710hp and their small (365cuin) BBC made 770hp and would run low to mid 8's. What is a stock BBC intake port entry, about 3.8sqin.

[Scotthatch]

Back around 1980, RM pro stock big sbc made 710hp and their small (365cuin) BBC made 770hp and would run low to mid 8's. What is a stock BBC intake port entry, about 3.8sqin.

How much of that power was camshaft rather than port?

[DrillDawg]

Who knows, I'm sure though both where maxed out, and I'm sure the BBC head was rubbed on so the port entry was bigger than stock. This was before they welded them up to roll them for reduced valve angle.

[Scotthatch]

Who knows, I'm sure though both where maxed out, and I'm sure the BBC head was rubbed on so the port entry was bigger than stock. This was before they welded them up to roll them for reduced valve angle.

My point is when you are porting and talking flow numbers it's all about the head the flow and the bench not the HP that comes latter the first goal is to see what you can do to make the head better ...

The other thing since you brought up a big block big valve rectangular port head maxed out is how is it getting used .... you go to the extreme and put that head on a school bus motor and it's just not going to work .... I have a set of sbc Pontiac heads that are just fantastic flow wise and a matching intake but I have to find the right use for them as depending on the cam they will peak at like 9000 to 9500 rpm

[DrillDawg]

LOL, I put them in the context of a pro stock engine, no where in sight of a school bus. But the the comparison shows the extreme differences of the CSA's between two similar sized engines and the results used for the same purpose. The sbc was just slightly slower at the time, maybe due to the weight and or development time in the car.

[Erland Cox]

To calculate the port size you need you need a formula for what you want your engine to do.
Max hp rpm and VE target.
Someone that I really miss here is Chad Speier and he has some helpful formulas on his site: http://speierracingheads.com/formulassites.html
Pipemax will make calculating easy for you.

Erland

[Scotthatch]

To calculate the port size you need you need a formula for what you want your engine to do.
Max hp rpm and VE target.
Someone that I really miss here is Chad Speier and he has some helpful formulas on his site: http://speierracingheads.com/formulassites.html
Pipemax will make calculating easy for you.

Erland

One of the problems with math and porting is the math tends to be idealistic and the port is anything but ideal ... with twists and turns and pinch points and intake runners mating up at angles that are not the same as the port bias you tend to do what works even though it doesn't match the math .... the good news is a running engine is a great averaging machine and if you are off a little it just balances out at a new rpm or HP

[user-30257]

Who knows, I'm sure though both where maxed out, and I'm sure the BBC head was rubbed on so the port entry was bigger than stock. This was before they welded them up to roll them for reduced valve angle.

My point is when you are porting and talking flow numbers it's all about the head the flow and the bench not the HP that comes latter the first goal is to see what you can do to make the head better ...

The other thing since you brought up a big block big valve rectangular port head maxed out is how is it getting used .... you go to the extreme and put that head on a school bus motor and it's just not going to work .... I have a set of sbc Pontiac heads that are just fantastic flow wise and a matching intake but I have to find the right use for them as depending on the cam they will peak at like 9000 to 9500 rpm

If they are 867 heads I bet even on a 290 inch sbc they won't peak that high.

Please stop posting your bullshit. People might take it for real info, like all your other posts.

[GARY C]

To calculate the port size you need you need a formula for what you want your engine to do.
Max hp rpm and VE target.
Someone that I really miss here is Chad Speier and he has some helpful formulas on his site: http://speierracingheads.com/formulassites.html
Pipemax will make calculating easy for you.

Erland

True! it may need testing and adjusting for ones application but it gives you actual numbers to start with.

[GARY C]

To calculate the port size you need you need a formula for what you want your engine to do.
Max hp rpm and VE target.
Someone that I really miss here is Chad Speier and he has some helpful formulas on his site: http://speierracingheads.com/formulassites.html
Pipemax will make calculating easy for you.

Erland

One of the problems with math and porting is the math tends to be idealistic and the port is anything but ideal ... with twists and turns and pinch points and intake runners mating up at angles that are not the same as the port bias you tend to do what works even though it doesn't match the math .... the good news is a running engine is a great averaging machine and if you are off a little it just balances out at a new rpm or HP

Did you actually take the time to study the info provided in the link or did you just discount it in favor of your theory?

[Scotthatch]

Who knows, I'm sure though both where maxed out, and I'm sure the BBC head was rubbed on so the port entry was bigger than stock. This was before they welded them up to roll them for reduced valve angle.

My point is when you are porting and talking flow numbers it's all about the head the flow and the bench not the HP that comes latter the first goal is to see what you can do to make the head better ...

The other thing since you brought up a big block big valve rectangular port head maxed out is how is it getting used .... you go to the extreme and put that head on a school bus motor and it's just not going to work .... I have a set of sbc Pontiac heads that are just fantastic flow wise and a matching intake but I have to find the right use for them as depending on the cam they will peak at like 9000 to 9500 rpm

If they are 867 heads I bet even on a 290 inch sbc they won't peak that high.

Please stop posting your bullshit. People might take it for real info, like all your other posts.

This is a little rude

You do know what's going on out in the world of engines don't you?? .... NASCAR has made rules for years to keep the rpm down ..... and I was kinda just chit chatting not outlining a build ....

http://speedsociety.com/the-12000-rpm-n ... credible/

[Scotthatch]

If they are 867 heads I bet even on a 290 inch sbc they won't peak that high.

Please stop posting your bullshit. People might take it for real info, like all your other posts.

This is a little rude

You do know what's going on out in the world of engines don't you?? .... NASCAR has made rules for years to keep the rpm down ..... and I was kinda just chit chatting not outlining a build ....

http://speedsociety.com/the-12000-rpm-n ... credible/

What is with dipshits always posting links to other bullshit.. 12,000rpm.. doesn't nearly sound like it. And if it is, I bet it's 3,000rpm past peak power and 2,500 past valve float.

You are welcome to believe what you want you can do a search and find all sorts of 10000 rpm sbc engines ....

As for the rest of what I post you have no say in it ... take it or leave it or post technical information that proves it wrong just making rude comments does not make you look like you know what you are doing .... I came here to pass on what I know ... I am not selling anything ... if what I pass on to others works then great if not then I hope something else does all I know is it works well for me and before I kick the bucket I thought others should know ..... that is kinda the point of this place isn't it?

[midnightbluS10]

If they are 867 heads I bet even on a 290 inch sbc they won't peak that high.

Please stop posting your bullshit. People might take it for real info, like all your other posts.

This is a little rude

You do know what's going on out in the world of engines don't you?? .... NASCAR has made rules for years to keep the rpm down ..... and I was kinda just chit chatting not outlining a build ....

http://speedsociety.com/the-12000-rpm-n ... credible/

What is with dipshits always posting links to other bullshit.. 12,000rpm.. doesn't nearly sound like it. And if it is, I bet it's 3,000rpm past peak power and 2,500 past valve float.

What's with dipshits coming on here to do nothing but start trouble and talk shit? THAT'S bullshit.