Auto Racing: air flow in standard amd modified engines, cubic feet per minute, revolutions per minute

Question
This is not really a repair question. Do you know the flow rate of air flowing through the carburetor of standard and modified racing engines? I'm looking for the rate of flow at idle up through high revolutions (ie. liters/sec or what ever units they are measured in.)  What I am not looking for is gas-air mixture ratios.  I have a design for a carburetor but I need to know a range of flow rates before I can start on a prototype.  At this point a general range is sufficient if that's all you know.  Also do you know any engineering types that I could contact about my design?
Tx Jim


Answer
Hi Jim:

Bsic air flow is a function of both the size of the engine and the size of the opening(s) through which air is drawn. On high horsepower racing V-8 engines a 750 CFM carburetor is a common installation. CFM is cubic feet per minute.

During one full revolution of the crankshaft, one half of the cylinders will have drawn in their full volumne of air (and fuel) exploded it and discharged it as exhaust. Therefore you can take the displacement of an engine  say 350 cubic inches times the revolutions per minute of the crankshaft (RPM), divide by 2,  and come close to determining how much air will flow through the carb. So your 350 cubic inch engine at 4000 RPM could draw 405 CFM of air.   Since no engine is particularly efficnent, I guess the 750 carb is enough.  Most street vehicles come with much smaller carbs.

My 1600cc Datsun race car uses one small Weber carb which we think flows about 300 CFM, but my above formula says something in the range of 195 is what it needs.  

Of course all this is also governed by the nature of the camshaft, valve gear,  and the true purpose of the engine.

This is the best answer I can give you at this time, however I would appreciate it if you would send a follow up quiestion or two after the weekend, I have two retired engineers available to me but I have to go to (dreaded) New York tomorrow 'til sometime Saturday, and I'm already running behind .

So do write back, i'm interested in your project!

Sincerely

Dan Liddy
Sarasota, Florida