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How much CFM is needed for 375HP?

Anyone know how much CFM of air is required to support 350 to 400 HP?

Not what size I/C is best.
Old 06-16-2008, 09:47 AM
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What size engine? How much boost?
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Old 06-16-2008, 10:57 AM
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3.2 Carrera at 7.5 lbs.
Old 06-16-2008, 11:26 AM
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I used:

displacement x rpm x 1/2 x volumetric efficiency x pressure ratio = cfm

so your engine would be:

193 cu in x 7,000 x 1/2 x .9 x 1.51 = 532 cfm

volumemetric efficiency may be below 90%, but that's what I used to be safe.
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Old 06-16-2008, 11:59 AM
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David,

I love this board.

So my minimum CFM for an I/C should be this or more?

Thx!
Old 06-16-2008, 01:25 PM
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I went more than the 749 cfm I calculated for my engine due to the rear placement of the intercooler. Sure an intercooler that's twice as big as it needs to be won't be twice as efficient and may only be a percent or two more efficient, it does give some margin for hot track days.

You'll also hear there's more lag with a larger intercooler, but one expert I talked to said if you go few days between a small and large intercooler you won't even notice any difference.

The big disadvantage to a large intercooler is weight. My intercooler weighs 30 lbs

If you're going to build your own, pay particular attention to the end tanks. I tapered mine across the inlet and exit to help keep the flow even.

As for front to back vs side by side, who knows? On front to back the air moves slower so it has more time to cool while a side to side has more velocity but each passage is longer so it has more surface area to exchange heat. ?!?!?!
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Old 06-16-2008, 04:59 PM
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Quote:
Originally Posted by 125shifter View Post
As for front to back vs side by side, who knows? On front to back the air moves slower so it has more time to cool while a side to side has more velocity but each passage is longer so it has more surface area to exchange heat. ?!?!?!

With all dimensions equal, the side to side(left to right) type flowing core would have a bit more pressure drop than the front to back style flowing core that has the shorter core path. It's why liquid/air IC's have such little to near zero pressure drop as the air passages that the charge air flows over are very short(average 2-4" at most VS 10-24" for various air/air).

A simple HP to CFM formula is:

Wa = HP x A/F x (BSFC/60)

Wa = flow in lbs/min
HP = horsepower target(crank)
A/F = air fuel ratio
BSFC = brake specific fuel consumption....usually estimated around .6

Then just convert to CFM

V = (N x 10.73 x T) / (29 x P)


V = CFM
N= lbs/min
T = Temp degree Rankine.......or outside air temperature plus 460
P = psia
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Last edited by BoxxerSix; 06-16-2008 at 07:34 PM..
Old 06-16-2008, 07:22 PM
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I understand the long IC's create more drag as the air cools and slows down.

Thought this is why CFM rating falls off so fast with added length.
Old 06-16-2008, 09:05 PM
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This turbo calculator will help with CFM calcs:
http://www.not2fast.com/turbo/glossary/turbo_calc.shtml
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Old 06-17-2008, 07:30 AM
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That's a cool site, thanks!
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Old 06-17-2008, 10:23 AM
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