Correct carb for 350 small block...650CFM??
 

What is the optimum carb for a 350 small block? Current setup has a 750 Holley double pumper. Previous owner installed cam, intake, headers, etc. Runs good. A little hesitation low end. I am thinking a 650 Holley. Any thoughts?
Thx Andy

750 is way too big. 600 or 650 would work.

The quadrajets that come on stock 350's are 750's. I've experimented on sbc boat motors and went from 500-850 the smaller carb will accelerate out of the hole faster than a larger carb. The larger carb will give you more top end. All depends what you want out of the motor. Pulling tubes / skiers may want a smaller carb. If its all about WOT use a larger one. The 750 should be fine. If your getting a stumble down low its not cause the carb is to big. Either the carb isn't tuned properly or timing is off, not advancing properly or something like that. Hope this helps you out.

Thanks for the info Black Baja. I will double check timing and carb settings. Andy

Do yourself the favor and go to this. I would never go carb'd again.

http://www.summitracing.com/parts/hl...FcFhpQodZnsAIQ

I read somewhere once the map is set you can go to a fixed map (open loop). No worries about O2 failures.

That's pretty cool. This winter project is actually my 69 Camaro SS so I'm trying to keep it vintage. :eekdrop:

Here is a link to Holley's website to calculate what size of carb you need and their recomendations.

http://www.holley.com/applications/C...bSelection.asp

•CFM = Displacement X RPM X VE / 3456
•Example: CFM = 350 CI X 6000 RPM X 90% Volumetric Efficiency / 3456
•CFM = 350 X 6000 X .90 / 3456 = 546.87
•CFM = 546.87

If you are after good performance do not go by the above formula.

A mild 350 (say 260-330hp) will be fine with a 600-650Holley. A 330+HP 350 will do well with a 750, especially if still running a dual plane intake.

I guess Holley should have contacted General Motors and told them they were using much to large Carbs on there motors. The CFM rating of a carb is measured at 1.5" of vacuum. An engine at W.O.T. Does not see 1.5" of vacuum. I don't think anyone uses that formula anymore as a matter of fact I don't know anyone that has ever used that formula. GM , Ford, Chrysler and Mercury surely didnt.

What he said!! My 355 has a proform 750 runs like a champ. Get some help to tune it. Stumble from idle could be squirter to small not enough pump cam, acc pump adjusted in properly. Could be a hand full of things. I used to run a 950hp on my 396 race motors. On the dyno it made more power but yeah I know it's diff in a boat!!!