Dynoed this winter, made 630hp and 640tq, that was with accessorys and my stainless marine exhaust, not stripped for dyno, I used 1050 Quickfuels 4150 style, the engines use 860cfm according to the dyno..

630hp only needs one 860cfm carb? Am I understanding that correctly?

No. A 860 carb would be an unnecessary restriction on a motor pulling 860cfm worth of air.

Ref

Tks
I was curious cause I am building 555's but currently am running 496's with 950 pro systems carbs (841cfm). I'd really like to stay with 4150 so will probably send my 950's back to pro systems and have them swap out main bodies? 555's are projected 700 hp and will run at 5,800. I would think I would need carbs to flow near 1,000 cfm. Any input welcome. Let's shoot for 50 pages lol...

I don't necessarily think CFM rating, is the only thing that matters when choosing a carb. While you need to be able to move enough air, there is more too it.

This is from prosystems website.

But really cfm is not the main level of importance. Fuel shear, atomization properties and fuel curve are your main areas of concern.

To size a carb for the application, you're looking to achieve minimal restriction at the finish-line yet have enough signal at launch as to be sure that the booster is atomizing the fuel and supplying the proper air to fuel ratio.

Horsepower equals air flow (of course). Launch rpm/trap rpm equals a reference of the range of the air flow.

If the carb is too big or signal/curve is too poor at the launch rpms created airflow, the fuel does not properly atomize and plates out (turns back to raw fuel) on the intake. Losses of 10-12 percent of available torque at launch can easily be recognized without a lean cutout or backfire. Then as rpms increase, the plated fuel is picked up and alters the air to fuel ratio down-track as it is cleaned out of the intake. More loss of power. So you jet it down to compensate for the plated fuel being picked up and the launch gets even worse. See the dilemma.

The wider the range of rpm you're going to subject the design to, the more you need to look at the range of airflow and available options.

I'm sure you remember this old formula:

CID x RPM x V.E. / 3456 = CFM

Well that formula is still being quoted by magazines and companies etc...but times have changed and carburetors are operating on almost immeasurable amounts of vacuum. 10 years ago a carburetor would require 10 inches of water to pull signal and shear fuel. Now they can can pull and shear fuel at only 3. Remember 20.4 inches of water (wet) is the cfm rating guide with reputable designers so we aren't looking to match cfm requirements with cfm ratings.

20.4 = 1.5 hg.

You can see that going from 10 inches of water as a requirement at launch to only 3 inches as a requirement really allows a serious increase in cfm size. This removal of restriction really pays off in cylinder head flow numbers and hp of course. Imagine altering this upstream restrictor when flowing your heads.

Because, most of you have specific application designs, a custom shop/unit is typically the plan.

In the future, use this calculation as a general rule on a modified carburetor:

CID x RPM x V.E. / 2820 = CFM
555 x 6000 x .9 / 2820 = 1062 CFM

Now you'll be a little closer.

A .9 Volumetric Efficiency (V.E.) number represents a pretty good combination and a 1.1 V.E. number represents an all out assault on the engine blocks stress handling capabilities.

Proform and Quickfuel worked together and came out with a 1050 4150 main body a few years back that alot of people have been liking. Needs 1 3/4 baseplate.

BTW: There's an 33 AT on another board that has 496's with out of the box AFR 315 heads, 1050 Dom (not done by any tuner shops), victor 454 R (dom) with Marine Kinetics cams that runs well into the 90's, Boat is on it's second owner now, and idle and etc is fine.

So, what do you do if you need 1523cfm of carb but you are using 2 carbs?

Different intake manifolds have different rules for carb cfm

Twin 2 barrel Rochestors?