[Boston71T37]

Motor specifics are unknown. Only info the seller gave was that it's a 69 350HO, which was wrong anyhow (1975 6X heads). Looks recently rebuilt with Edelbrock Performer manifold, HEI distributor and a Carter 625cfm. If I plan to replace the motor with a 455 anyhow...would I be able to get away with a 750-780cfm carb?


https://www.youtube.com/watch?v=1P71...e_gdata_player

[john65ss]

Q-jet - no better choice for a street car.

[Cliff R]

Depends on the power level. Even the smaller 750cfm q-jets are plenty of carb for the big 455's to at least 500hp. I've had engines on the dyno and at the track and swapped carbs from 750 to 850 cfm on them many times. Interesting that the smaller carbs do fine to at least 4500rpm's or so, even feeding pretty high powered/big CID engines.

Actual track numbers on my own car don't vary all that much from 750 cfm to 850cfm. I did quite a bit of testing with my old engine at 514hp/587tq. Not much more than a tenth of a second and 2mph difference swapping back and forth between a 750cfm, 800, and 850. As power level goes up, I'm sure the larger carbs may show more spread. For under 500hp, at least from what I've seen, 750cfm is PLENTY of carb for a 455 cid street/strip Pontiac engine.....Cliff

[Boston71T37]

Thank you very much for the advice, feedback and data! I picked up a Quick Fuel HR-680-VS Hot Rod Series Carburetor (electric choke, vacuum secondaries) to replace the 625 competition series 4bbl on it now. Hoping that it isn't ovekill. We shall see.