While it is common knowledge that 'over carbing' is very common for the street with hot motors kind of crowd (that would be us
), I remain skeptical of the mathmatical formulas used to calculate carb cfm requirements. Perhaps the problem lays with the 'guesstimate' of engine VE.
NASCAR running 80 to 90% VE? Hard to belive it's that low, unless the race team WANTS you to believe that. Or perhaps thats as measured with the restrictor plates in place, something 'we' don't have to run.
I have a hunch that many of us have engines with well designed heads and combustion chambers that can run 90% or BETTER VE. Not the majority of course, but I suspect a significant number of us could and do.
In addition, there is more to a carb than just it's CFM rating that makes one carb superior over another. I was running dual 660's 'race only' at the track (terrible on the street). Thats 1320 cfm, carb calculation math would easily conclude I was over carb'd. Not to mention jets so fat it ran rich with an air cleaner! But hands down that dual 660 carb setup was quicker in the 1/4 than any other of the combo's I tried. Solid roller cam, 12.5 to 1 compression, high riser heads and shift points just above 7000 rpm, 427 side oiler (severly traction limited
). I could 'run it out the back door' in third!
Simple explanation of VE (volumetric efficiency): If the size of the cylinder is a 1000 cc and the intake stroke can FILL that cylinder with a 1000 cc of air/fuel, thats 100% VE. 800 cc is 80%. It's easy getting the fuel in, much harder getting the AIR in.