Which carb(s) is better will be determined by the particular engine combo it's used on, every engine has different fuel needs. Keep in mind that carb cfm ratings are based on demand, most won't flow thier maximum advertised cfm unless under idealic circumstances. most carburetors flow much less than advertised during normal use.
If you've ever had trouble figuring out what CFM carb your engine might need the formula below can be helpful:
Multiply your engine's CID by the RPM of the engine,
Divide the number by 3,456. Multiply the quotient by your engine's VE (volumetric efficiency). VE is a measure of how efficiently your engine pumps air. Generally a stock engine has a VE of .8, a race engine should be valued as .9, multiply this value by 1.35 for the minimum cubic feet per minute (CFM) rating that your engine can use. The CFM rating is used to classify carburetors, based upon how much air will flow into a WOT carburetor. The reason your results must be multiplied by 1.35 is that most carburetors work in pulses, and as a result intake will often be slightly above or below its average rate. The 1.35 modifier ensures that your carburetor can handle your engine at its maximum output. You want a carb that is equal to or greater than your final answer.
Example, my engine: 340 Stroked to 426 cubes, max rpm 5,700rpm.
426 x 5,700 = 2428200
2428200 div/ 3456 = 702.604 x .9 = 632.343
632.343 x 1.35 =
853.66 cfmThis tells me that when my engine is at full song at 5,700 rpm it
could need as much as 853cfm of flow to keep up with it. In my case an unmodified 800 cfm TQ may fall a bit short, but a 1,000 cfm TQ should do the trick with a bit of room to spare.
