I've confused myself... - Team Camaro Tech
Engine General Engine Discussion.

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post #1 of 8 (permalink) Old Dec 20th, 16, 10:48 AM Thread Starter
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I've confused myself...

This all started innocently enough as I was trying to calculate how much intake head flow I needed for a 350 at 6500 rpm. So, 350/8 to get cylinder volume, (43.75 cu in); convert to cubic feet, ( .02531829 cu ft); and multiply by half of the rpm in question since the cylinder only draws in air every other stroke. That equals 82 cfm. That seemed wrong so I did it again and then realized that there was fuel in the air as well. sigh... Well, I used the Stoichiometric value for fuel and a density mark of 75 degrees f to end up with an answer, that again, was confusing. I then realized duration was in effect as well and lift. I figured out the average duration based on a comp 276 roller and then quit when I realized I could just ask you guys.


What flow head flow numbers support a 350 at 6500rpm? Is it proportional when looking at a 383 or 406? Is intake flow more important than exhaust? I know this is all going to be relative to the cam, carb, heads, exhaust and intake playing well together; I'm just confused...


- Rob

1968, 5 speed, Vintage Air Gen IV, American Auto Wire Update Series, Champion 4 Core Rad, BMR front w/ Koni's, BP Roller 383, Posi 8.2", Solid Frame Bushings
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post #2 of 8 (permalink) Old Dec 20th, 16, 11:53 AM
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Re: I've confused myself...

Math can be fun I guess, But I'd just call AFR, DART BRODIX.. and ask
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post #3 of 8 (permalink) Old Dec 20th, 16, 06:57 PM
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Re: I've confused myself...

I can see why you are confused.
Don't worry it happens to me all the time.
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post #4 of 8 (permalink) Old Dec 21st, 16, 12:53 PM
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Re: I've confused myself...

I may be totally missing it here, but could it work if you start by use the number arrived at by calculating induction size as a baseline, then dividing by number of cylinders ??? There are multipliers in the formula for street and strokers engines.
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post #5 of 8 (permalink) Old Dec 22nd, 16, 11:12 AM Thread Starter
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Re: I've confused myself...

Quote:
Originally Posted by KRhat View Post
I may be totally missing it here, but could it work if you start by use the number arrived at by calculating induction size as a baseline, then dividing by number of cylinders ??? There are multipliers in the formula for street and strokers engines.
I wanted to calculate the flow needed in lieu of the runner vol due to variances in head design. I figured if I knew what flow numbers I needed, I could then look for a head that flowed that amount. What I'm finding is that people like the AFR 180s for a very good reason. Lol

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post #6 of 8 (permalink) Old Dec 22nd, 16, 07:33 PM
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Re: I've confused myself...

Rule of thumb is to double the intake port CFM = peak horsepower.

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post #7 of 8 (permalink) Old Dec 22nd, 16, 09:17 PM Thread Starter
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Re: I've confused myself...

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Rule of thumb is to double the intake port CFM = peak horsepower.
Thank you Sir. If I may, is that at peak or average throughout the lift range?
- Rob

1968, 5 speed, Vintage Air Gen IV, American Auto Wire Update Series, Champion 4 Core Rad, BMR front w/ Koni's, BP Roller 383, Posi 8.2", Solid Frame Bushings
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post #8 of 8 (permalink) Old Dec 23rd, 16, 07:39 PM
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Re: I've confused myself...

Peak HP
Here's some info: How Much Power Can A Given Cylinder Head Support? - Hot Rod Network
You will notice the HP is about double the CFM given. This assumes a pretty racy engine, probably not a street cam.

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