Can someone give me the formula to calculate the CFM (cubic feet per minute) for an exhaust pipe. Just give me the variables please. Thanx!!

 

Well i cant give you variables, but maybe it doesnt have to be this hard, lol. Are you using this to get a idea for exhaust diameter for a turbo app. or whats being done?

 

I am not sure that CFM's can be calculated. you can take 2 pipes that are the same size ones straight and the other has two bends in it and they dont carry the same cfm values. I do know that they make a machine that can determine cfms but only really speed shops that do a lot of port and polishing have this. I imagine it is not cheap.

 

well, its actually for a supercharger. i need to know how much air it is going to push in, so then i can know how much to push out. im going to running about 8psi, but i want to have an exhaust that can easily remove that air. i already have a plan for the exhaust, i just need to know a good diameter and how many bends

 

The bends would make it complicated to work out the volume, would be simple for a straight pipe but for an exhaust it would be really awkward to work out.

Could always take it off, weld up one end and fill it with water then measure how much water it took to fill the sucker up

 

Volume still does not determine cfms. volume actually has a simple formula for that, but for any kind of boost app 2.5-3.0" piping will yield your best results. of course if you really want to know put one on then dyno it then do the other. but still not best way unless you own a shop with a dyno which you wouldnt be asking this question if you were. there is no diffintive answer for cfms on the exhaust side but you can limit your bends to the bare minimum and expect more power out of it but then you also have to take into consideration is backpressure, a good exhaust system should have right around 1psi of backpressure and no more than 2psi.