Racing Fuel Systems

Don’t know if this has been done to death or rarely ever raised. How do you guys decide on cfm for your application?

I remembered this chart at the back in the technical section of a 1987 Holley catalog:



Very different from the mathematical formula that has been around a long time - ci x rpm x VE / 3456 = cfm. Another version being ci x rpm x VE / 2820 = cfm

Thoughts on both methods above and how do you hone in on cfm for your combo?

Discuss.

That's old, doesn't account for newer engines efficiencies, higher stall converters, vehicle weights, gear ratios...

A chart isn't realistic, too many variables. That chart was designed for the average street car 40-50 years ago. And then you have manifold designs, booster types, I find with annulars you can put a bigger carbs on and still get great throttle response.

I assume this chart (and the formula) is based on WOT. Do you give up part throttle response running a 750 vs a 600 on something like a 400 ci mild street engine? Would the difference be something the average driver could perceive?

Here's Holley's latest recommendation:



Looks like the recommendations are very close to the original. Question then might be do the HP's flow more air and how much?