Pyper6970 said
I guess it depends how much hp you plan on running. I have found that when it comes to 4-bbls on the street, there is no evidence that you can get any more than about 1.8 cfm per hp. Race cars can go to 1.6 cfm per hp, NASCAR's can run as little carburation as 1 cfm per hpSo if you have

a 390cfm, 217 hp likely, 244 hp net race spec, 390 hp absolutely wrung out on an optimised engine with perfect cam and induction.

A 465 cfm, 258 hp likely, 291 hp net race spec, 465 hp absolutely wrung out on an optimised engine with perfect cam and induction.

A 500 cfm, 278 hp likely, 313 hp net race spec, 500 hp absolutely wrung out on an optimised engine with perfect cam and induction.

A 600 cfm, 333 hp likely, 375 hp net race spec, 600 hp absolutely wrung out on an optimised engine with perfect cam and induction.

A 650 cfm, 361 hp likely, 406 hp net race spec, 650 hp absolutely wrung out on an optimised engine with perfect cam and induction.

Deal is, if the carb is not likely to be over taxed, then you need to look at its tuning jet wise, or somewhere else in the engine.

One point of note. The 390 cfm carb has a very restrictive choke to throttle profile, its a carb that has "a thin waist with broad hips". This means it has great drivability from a strong signal, but it is more restrictive than a 500, 600, or 650 in profile.

Such a profile won't produce as much power as some of the other Holley carbs.

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A FordSix.Com refugee. Former Aussie 225 AP5 owner. Non-violent, and totally aware of Slanted Chry-Power.