To put some numbers to Jerry's comment:
GM used a number of different carburetors (of different sizes) on the 248. Different size carbs were/are used to maximize torque for heavy duty trucks or fuel economy/performance for light duty trucks or.....
The point being, a group of engineers made some decisions.
If we look at one of the larger of these carbs, a Zenith type 228 with a 33 millimeter venturi, we find from Zenith data that this carburetor would flow approximately 230 CFM.
However, quoting from a very obnoxious TV commercial...BUT WAIT!
CFM for 1 and 2 barrel carburetors is measured at a vacuum represented by 3 inches of Hg, whereas the Holley 390 CFM is a 4 barrel which is measured at 1 1/2 inches of Hg. To convert from the 1 barrel scale (the Zenith type 228 is a 1 barrel) simply divide the 1 barrel rating by the square root of 2 (1.414) reference:
http://www.thecarburetorshop.com/Carbshop_carbsizesandCFM.htmSo dividing 230 by 1.414 we arrive at the figure of 163 CFM (the figure that the GM engineers determined was on the high side for necessary air flow for a 248.
So the small 4 barrel Holley 390 is more than twice the CFM that the engineers determined was the maximum size needed for a 248!
OK, so if this thing is going to be placed in a trailered race truck, and umpteen thousands of dollars are going to be spent in R & D of special engine parts to either (A) SIGNIFICANTLY improve the volumetric efficiency of the engine or (B) more than DOUBLE the useful RPM limit of the engine then MAYBE the small 4 barrel would be useful.
But of course anything is useful to bench racers.
And Martin, no offense, but must disagree; they DON'T look cool to non-dreamers. They just scream that the owner is descended from SGT Schultz!
Jon.
