IIRC the front 2 barrels of a Q-jet with the small Venturi is only something like 229 cfm at 3.0 vs 210 cfm at 3.0 for a mono jet used on stock 250s. Not much different. By limiting the rear air valve opening the total carb cfm can be not quite 500 cfm at 1.5 hg. However a lot of people would rather have a Holley or a carterbrock because they are easer to tune. Nothing wrong with any choice, most people like me stick with what they know. How much cfm does the Primary's of the Holley Q jet replacement carb flow? I think it is a 4165? I am talking about the Holley that was bought as a bolt on Q jet replacement. Is it a double pumper? Clearly I don't know much about Holleys but am eager to learn. I didn't even know that the 390 was expensive until this thread. Thanks everyone for helping me learn about Holleys. Jay6155
