Woah! Went to the dyno - Jet Sizes!

[Len Hurlburt]

I agree with the others the carb size you are currently running should be more than enough. We put a friends 418ci stroker on the dyno, and after optimzing the jetting ( I don't remember what we sizes we ended up with), our best pull was 399hp at the rear wheels with a 650 Race Demon. With no other changes, we swapped the 650 out for a 750 Speed Demon, and after doing some jetting swaps, we ended up with 405hp at the rear wheels. We decided to reinstall the 650 as it provided much crisper response in the lower and mid RPM ranges where the motor would be mostly operated.

[55312]

I put a new Holley 4150 650 CFM on my 427 FE last fall - rejetted it and it made a huge difference in AF ratio and responsiveness. We did it all on a chasis dyno and I was told to stick with the smaller carb if I wasn't looking for top end. I don't race it and won't beat the 1963 vintage block by maintaining the high RPMs needed to see the difference in HP of a larger carb. I'm happy with the 650.

Tim

[Tongue Pirate]

As well, I ran a 600 DP on a 454 BBC at one point which ran much better than a bigger carb. As stated the key is the RPM range you will be operating in.

[CobraEd]

A single plane manifold can typically get by with a smaller carb than a dual plane manifold, but it also required more jetting.