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with a slightly bigger cam there usually no issues.

my cam is 250 duraration at .050 and 275 lift. vacuum is in the dumpers measuring about 7-8" in gear. does that explain why they need some massaging?



Relatively stock engines will likely be fine, depends what you see as fine though. My Dad had zero problems with his 6pak till the 509 cam went into the 440. even then it wasn't too bad. The real challenge to tuning came with the 496 stroker and a 251 @ .050 and .570 lift cam.

I have drilled out the primary butterflies to 1/8 inch and given him about 18 degrees initial and 34 total timing but the timing is all in at 1000 RPM or a tad less. I believe he has a 55 powervalve with jets being 64 or 66 middle carb, and about 84's in the ends. Can't remember if he stagered them or notThe other thing was a 50cc acc pump and put the pump cam in the #2 position to move more shot into the 1/2 to 3/4 throttle range. We have tried all the springs Holley has for the secondaries but have ended up running Purples (one step heavier than stock IIRC) which has resulted in best times so far but that is in a 3700 lb Challenger and driver with 4.10's and 29 inch tires. We are still playing with it but right now it seems to work Excellent.

P.S. , If "Cab Burge" gives you advice, listen to him, he knows these carbs VERY well.

Don.