My newly installed 409/340hp has the stock Rochester carb (rebuilt not jetted) on it and runs pretty strong. I was wondering if I could get more performance from a Holley 670-750cfm carb? It seems Holley's don't produce as much torque (articles on Holley's) as the stock Rochester, but may produce more horsepower. I am trying to keep the motor as stock 'looking' as possible (air breather will cover most of carb) while trying to get some good performance. I have a mild cam(.528/268I, .526/275E), roller rockers, dbl roller timing chain, stock exhaust manifold, 2500-3000rpm torque converter, stock 340hp block& heads, 370 posi rear end and stock suspension. Using the formula CFM=(RPMXCID)/3456, with 4000rpm's cruise speed puts me around 670CFM (375 primary).