carb cfm for 383

Avs = Thunder series. If ultimate performance is not your goal, a 650 will be fine. A 650 will give you nice throttle response but may sacrifice some performance at high RPM. For my 440 I have chosen to run a street demon. They make a 625 that has received good reviews. In theory it takes the best of a AVS and Holley and combines in to make a square bore thermoquad. I have not run mine yet, so no input on how it actually performs.