/6 cRaZyNESS

273 said

So basically a 500 cfm 2bbl is half of a 750 cfm 4bbl.

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Not really. A 500 2bbl will flow 500 cfm at a pressure drop of 3 inches across the carb. A 500 4bbl will flow 500 fpm at 1.5 inches pressure drop. Since most every one is used to the rating on 4 bbl carbs (at 1.5 pressure drop), if you use the same pressure drop (1.5) on the 2bbl, that carb only flows about 375 cfm. But since the 2 bbl has much bigger barrels than the primaries of the 4 bbl, you lose velocity and drivability with the 2 bbl (as compared to the 4 bbl).
PS: I know several slant six racers that do run very large 4 bbls on their engines. But these are race engines with high stall converters and low rear gears, that don't need low speed throttle response. I know of one slant sixer that used an 850 TQ. Very small primaries and hugh secondaries. That was hard to tune the transition to the secondaries.