Inliners International Forums General Discussion Hi Performance 600 CFM ON A 250

I ran two diff holleys on my '67 half ton short wide bed 250 with a cliff intake and hedmans/flowmasters. The first was a 450 cfm holley "economaster", a small butterflied carb like a wcfb/4GC, but with MECH. secondaries. With a certain amount of "copying" from a holley book, I was able to duplicate the mods holley said was necessary to run it on a 238 buick V6 (close enough in size-my carb was a replacement on a 350 chevy). After mods,(one of which was to add a set of idle holes and transfer slots under the SECONDARY butterflies to handle the slight bogs) this was a nice carb.

Later I put on a stock 600 cfm "belly-button" holley with vacuum secondaries (NO DOUBLE PUMPER). With virtually no mods, other than idle screw and pump adjustments, it ran real nice too. It seemed that since the back barrels would not open 'til engine needed them, that the old 3.70 geared truck had more pep (from bigger front bbls than other carb) at bottom end making it the more fun of the two carbs.

Now aint those front bbls on the 600 the same setup and situation as a 500 cfm holley TWO BBLs have?. Therefore why cant the 500 two bbls work well on 250s? Most overcarbed motors are going to exhibit bogs, and stumbles. The 600 cfm was really nice, and so was the smaller 450 cfm mech, no-vac secondary carb(after modin'). Vacuum controlled secondaries is the saving virtue. Q-jets, factory mopar thermo-quads ('cept they got a lotta smog stuff on 'em) an' I guess a pair of Pintos too, and most controlled (mech or vacuum-vacuum the better) secondaries carbs should work fine. There are some good carb books on the market-ya ges gotta find 'em and read'em snowman.