cfm of motor at rpm

evanesce69 · Aug 8, 2008

ok, I've worked 62 hours in the last 5 day and have had maybe a days rest. this project is becoming very time consuming (and i dont mean my E85 ambitions)

I take tonight off.

... as the vodka settles in i find myself getting less adept....

my fellows, how do i calculate cfm at a specified rpm??

I'm assuming that in one rev of the crank, our engine displaces 3.0L of "air"

1 RPM = 3.0L air in 1 min
3600 rpm = 3(3600)L air in one minute

(i'm getting lazy and leaving out the units)

10800L/min = 381cfm

am i right???

Just_Randy · Aug 8, 2008

You'd be right if the engine had no intake restriction. The 3 liters is the volume of the region of the cylinders that the piston moves up n down in. Not the volume of air that actually enters. That has to do with how far you have the throttle open and how well your intake flows, valve timing, port flow, etc, etc. According to dyno2k, its more like 150 @ 3500. And 250 is about all that engine will ever see at any rpm.... unless you have forced induction. In that case you might get close to 400 at top rpm.

You can arrive at the same numbers here: http://www.usaimports.co.uk/Carb_Calculator.htm

Put in 2, 3000, 3500, and 83% is good enough.... 153 is the result.

inferno94 · Aug 9, 2008

evanesce69;186748} I'm assuming that in one rev of the crank said:
You must remember this is a 4 stroke motor ie only 1/2 the cylinders are injesting air per stroke. So the engine consumes 1.5L per rev at WOT.

cfm of motor at rpm

evanesce69

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Just_Randy

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inferno94

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