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Discussion Starter #1
Trying to learn me some things.

Let's say for peak power at 6k rpm, what is better?

A set of heads with smaller intake cc that has better flow numbers at a given lift.

Or

Not as good flow numbers but with larger intake cc.
 

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I’m guessing smaller cc with better flow.
Every engine combination wants a specific "size" port. Not the smallest, not the biggest, but the right port and valve. It has to do with cross sectional areas and velocities more than raw airflow. A big port with poor airflow will have low velocity and poor cylinder filling. A small port with a lot of airflow will have high velocity and may be too small and be a restriction. The right port and valve will have the ideal airspeed for the given engine displacement, rpm and intended use.
 

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calculate the cross sectional area you need for your application
work on the shape of the runner, valve size and throat.
Then worry about flow numbers.
A Program like pipemax can take a lot of the work out of the process and is well worth the investment.
 

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Discussion Starter #9

Have a look at this thread ^^^
Did you just suggest I read 177 pages of shit to get an answer. Do you suppose there is a summary somewhere? :D
 

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Discussion Starter #10
calculate the cross sectional area you need for your application
work on the shape of the runner, valve size and throat.
Then worry about flow numbers.
A Program like pipemax can take a lot of the work out of the process and is well worth the investment.
We're not even speaking the same language here.

You want to break that down for me? Im not an engine builder. Just happen to be building an engine. Actually, I already have heads, just wad thinking out loud asking questions to gain some basic knowledge.

Not sure why im on the bullet for that.. but here I am!
 

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Your question is to broad, he's telling you you need the right size and shape of port for your engine's size, rpm range and horse power desires. It might be helpful if you list your engine and heads you have so people have something to work with, other than that the smaller port that flows better is best as it should have more power below the power peak even if the heads flowed the same, but the right size is the best size.
 

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Did you just suggest I read 177 pages of shit to get an answer. Do you suppose there is a summary somewhere? :D
I think you should read that complete thread and any others that you can find and after awhile you will see a pattern and know the answer, you have to feed the engine the right volume at the right velocity and as the rpm's raise the less time you have to do that.
 

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Velocity tied with CFM is the key as stated earlier. If you have a port flowing 400cfm but it's velocity is 250m/s then it will act like the old Ford 302 Trans Am engines that needed to buzz at high rpm to maintain power. Somewhere in the 280-320m/s range is where you want to be. So what ever port gives you that is what you want. If you see the cfm numbers stall at a certain high lift most likely the charge is slamming against the back wall and you'll want to slow it down at that point. Even more to read. Techtips - Cylinder Head Math for Engine Performance
 
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