# Pressure & CFM through port

I'm generally pretty good with mechanical physics, but I haven't taken a fluidics class yet to know how to answer my own question-

On our racecar (http://www.mcdermottfamilyracing.com [Broken]), we have a scoop of given dimensions (that i dont have yet, but will get soon). It's of a trapezoidal shape, but I'll get what I can.

We have an air pan under the scoop, so that the area within the scoop becomes pressurized, and "rams" the air into the carburetor.

It's a 4 cycle engine, so here's my best theory on how things work-

6800 RPM at half track (330 feet) @ 97 MPH

6800 RPM * (2 RPM per intake stroke per cylinder, for a 4 cycle engine) = 3400 intake strokes per minute

3400 intake strokes per minute * (arbitary time period, say 1 second) = ~57 intake strokes in that one second

57 intake strokes/sec * 505 cubic inches = 28,785 CI/sec = 16.7 CF/sec

So at half track @ 97 MPH, we're drawing about 16.7 cubic feet per second OUT of the scoop

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7300 RPM through the lights (660 ft) @ 119 MPH

7300 RPM * (2 RPM per intake stroke per cylinder, for a 4 cycle engine) = 3650 intake strokes per minute

3650 intake strokes per minute * (arbitary time period, say 1 second) = ~61 intake strokes in that one second

61 intake strokes/sec * 505 cubic inches = 30,805 CI/sec = 17.8 CF/sec

So at half track @ 119 MPH, we're drawing about 17.8 cubic feet per second OUT of the scoop

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Since I know how much volume I'm drawing out of the scoop, the air velocity coming into the scoop (assuming same as car speed), and if I find the area of the scoop opening, is there a way to find the pressure inside the scoop?

Edit- The opening is 12" x 14" x 3.5". (B1+B2)/2 * h = 45.5 square inches.

The Scoop's internal dimensions are roughly 23" deep, 16" wide, 5" tall. The back is blocked off vertically, so it represents somewhat of a rectangular prism. The air pan blocks off the bottom so it's uniform flat from the front of the opening to the back plate.

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Gold Member
If I understand you correctly, you want to know how much boost ram air gives you. It depends only on the vehicle speed:

boost pressure = V² / 56818

Where the boost pressure is in psi and the vehicle speed V is in MPH.

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