[Ronnieroadster]

Originally Posted by JWL

First, we must be clear on whether this is blow-thru, or not? Probably not, but it makes a difference. The ideal size 4 barrel carb for a small street Flathead is the 465 CFM Holley. This is especially true where good usable low speed torque RPM is desired while maintaining good top RPM HP. But, even more important than specific CFM sizing, is the requirement for jet sizing to be safe. I suggest a good A/F ratio meter so you can start somewhere in the 11 to 12 area while seeking the ultimate for your combination. The ignition combination will be a consideration to make the best use of the new blower.

465 CFM is in no way adequate for any supercharged flathead application. The throttle response as well as the lean out situation with that size carb will cause issues. Your way to lean. Be very careful because your going to burn a hole in the top of a piston being to lean. My extensive real world hands on experience has shown the minimum needed CFM is 600. Jet sizing from the out of the box Holley is an excellent point to begin with. The 600 Holley with the vacuum secondary will work perfectly. Flathead V-8 supercharged set ups using a GMC blower will easily produce 8 pounds off boost when under driven as much as 20 percent even the 371 which by the way has the carb sitting on top of the blower. With out the proper CFM damage will result.
Ronnieroadster

P.S. ignition should be a minimum of 8 to 10 degrees initial with a total of no more than 20 degrees. Ask me how I know