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post #1 of 4 (permalink) Old 04-18-04, 07:39 AM Thread Starter
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Measureing CFM??

How do you measure the amount of CFM that your car intake will allow?


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post #2 of 4 (permalink) Old 04-18-04, 09:37 AM
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Re: Measureing CFM??

Airflow in CFM = (Engine Cubic Inches x Maximum RPM) 3456

This formula assumes 100% volumetric efficiency but the real world figure is around 70-80% so it pays to subtract 30-50 cfm from the result to provide a more realistic figure. For example for a high performance 350cid street car|:

350cid x 8000rpm 3456 = 810cfm

Subtracting 30-50cfm brings this figure back to around 750-780cfm.

From http://www.cortina-mk1.com/carby.shtm

Took me under 1 minute to find it from using a search engine - it would probably be quicker for you to try this method next time than waiting for a reply.

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post #3 of 4 (permalink) Old 04-18-04, 11:37 AM
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Re: Measureing CFM??

I thought that formula is for working out what size carby to use, where as i think Casper wanted to know the max CFM of a manifold?

I guess you would need a flow meter?
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post #4 of 4 (permalink) Old 04-18-04, 02:52 PM Thread Starter
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Re: Measureing CFM??

Yeah, I already know what my engine requires, the formula is easy enough to find and work out.
Now, how to I find out if my current airbox/intake setup allows this sort of CFM to actually occur? I mean, it's all well and good for the formula to say I need 330CFM but the intake is trying to suck through a straw that simply cannot flow that amount!! What I'm trying to find out is what my intake can actually flow!


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