cfm rating

What is the cfm rating for the rochesters on our 350's. Is there a difference between years and motors?

 

According to the Rochester carb book by Doug Roe, starting in '71 Buick started using the 800 cfm Quadrajet for the 455 and the rest used 50 cfm less. So I take this to mean that the 350 motors used the 750 cfm carb. In any case, do not use a carb smaller than 750 cfm on a 350 Buick motor. Mark:beer

 

i've been told basically all 350's used 750cfm carbs...i thought that included pre-71 350's, too, but knowing me i'm probably wrong.

and the general knowledge is that buicks like big carbs...750 is a good size. larger ones are said to give better top end, but they might cut into acceleration.o No:

 

I suppose if your 350 goes to the strip, or gets into street racing, 750cfm is what you want. Someone put a 625 Carter Competition Series carb on mine about 6 yrs ago, with a fairly mild 350, stock intake/exhaust, mild street cam. I just see typical city/highway miles with mine, no drags, etc., and it runs great. I get excellent acceleration, and good hwy mileage, upper teens, and great idle manners.

 

Regarding carb size, there was a long thread about this on the BCA Performance board about two years ago.

The thread concerned the 300 engine. There were many postings. One respected poster gave an explanation that the 300 engine could not utilize more than 500 cfm. He gave a formula that the other posters agreed with. His statement basically ended that discussion.

I keep thinking how that logic conflicts with the statements I see here about 750+ cfm for a 350.

Am I missing some major difference between the 300 and the 350, or just different experience and philosophies among posters?

 

That formula in the QJet and the Carter books is a generalized formula that will put you in the safe ballpark for generic cases.

Somewhere, Jim Burek stated the reason why 400/430/455 engines love really big carbs, much bigger than the formula yields, is because the intake and port volumes are small in relation to the amount of air that flows through them. Experience has also shown that the 401/425 Nailheads and the 350 also easily handle large carbs, and perform better with bigger. On a 300 Pinhead, I haven't heard if bigger is better. In the practice of engineering, you start with formulas, but then there's that 'Integration' phase where you actually make the thing work, and sometimes the formulas don't hold up.

Back to the original question - all 350's were the 750 cfm variety. It's in the Chiltons and Motors manuals as bore and venturi size, bounced against the Roe book which states and shows a picture of the 800 cfm bores and venturis.
:Smarty:

 

Experience talks.

I'd listen to what the others are using.

I also Know that it depends on what Type of carb it is. How? Because Holley's with mechanical secondaries can be sized a little larger due to the dual accellerator pumps. Their catalog says that a 350" street / strip engine can use their 04779 750 CFM double pumper. That's what I use and there is no bog at all! This is with a 5 speed trans.