8duallup
05-17-2005, 08:59 PM
how big of a carb does your engine really need?
to find out do this--engine cubic inch displacement (x) maximum rpm's (x) volumetric efficiency/ 3,456.
CID x RPM x V.E. / 3,456 = CFM
its a good start, but there are also a lot of variables that can come into play such as: weight of vehicle, gear ratio, intake manifold, camshaft, and so on.
a rule of thumb-- the correct cfm carb will cause the engine to have 1 in. of vacuum at wide open throttle with the engine at peak rpm's. if the engines vacuum is below 1 in, the air speed is too slow. (not mixing air and fuel together properly) if the engines vacuum is above 1 in the carb is too small and is acting as a restriction to the engines's demand for air fuel mixture.
to find out do this--engine cubic inch displacement (x) maximum rpm's (x) volumetric efficiency/ 3,456.
CID x RPM x V.E. / 3,456 = CFM
its a good start, but there are also a lot of variables that can come into play such as: weight of vehicle, gear ratio, intake manifold, camshaft, and so on.
a rule of thumb-- the correct cfm carb will cause the engine to have 1 in. of vacuum at wide open throttle with the engine at peak rpm's. if the engines vacuum is below 1 in, the air speed is too slow. (not mixing air and fuel together properly) if the engines vacuum is above 1 in the carb is too small and is acting as a restriction to the engines's demand for air fuel mixture.