Inliners International Forums General Discussion Hi Performance Carb cfm with B&M 144 blower

What size suggested four barrel carb to use on a B&M/Weiand 144 blower on a 261 Chevy inline 6. Max rpm 5000-5200. Engine has forged/dished pistons, GMC rods, pretty radical solid lifter cam (I do not have the cam specs handy now) 700r4 trans, 4:11 rear gear in a 54 Chevy passenger car. And yes, I do know about the boost reference power valve use. Mostly just need to understand if carb cfm is more tied to the blower size as opposed to the engine cubic inch etc.

All input appreciated, Eddie

For draw-through the CFM should match the usual calculation × the blower's pressure ratio (not boost).

I would say a 600-650 would be a good choice.
Years ago a girl named Marry had a nice (IIRC) 65 Nova w/a 355 SBC & a Weiand 144 blower & the blower chart (B&M) for that size engine & blower a 750 was supposed to be the biggest she should use, she tried it, it ran good, then she wanted to see if a 850 would work better, she ran a 1/2 second faster in the 1/4.

So even those charts that B&M had are just good reference charts, there are many variables that can change what is needed.
MBHD

You can use a smaller carb if you like, just will not get as much power & boost.

Math example:
261 × 5,200 × 90% VE (it's probably less) × 1.1 correction for L6 ÷ 3,456 = 389 CFM normally aspirated.
10 psi boost is about 1.68:1 pressure ratio (based on ATM = 14.7), yields 653 CFM.

Hey, I made a good guess?

MBHD

Don't be modest - that was experience and a good memory.

I don't understand the "x 1.1 correction for L6". Why is this necessary? Thanks.

The demand interval between intake cycles is different with less than 7 cylinders; a single needs way, way more cfm than the formula. An L6 needs only about 1.1 (V8 etc. are 1.0).

Thanks for the explanation.

Thanks for all of the input given as to CFM rating. Now my next question is what brand/type of carb and the needed modifications. I am not especially fond of Holley carbs but will consider all opinions.
Thanks again to all that have advised.

I have a 270 gmc with a 471 an a 600 edelbrock. it pumps about 13 psi at wot. the carb is easy to tune and seams to perform good.

Both the Holley 4150 type and the Carter AFB have been done so many times that advice is easily available. Anything newer and you're doing your own research.