Carb CFM recommendations

RustyRatRod said

Wrong. The 1405 can have the choke added easily. The difference is exactly as I described. The 1406 is very lean. The 1405 is tuned for performance. There's a thread on it around here somewhere showing all the differences. The passages in the boosters are different. The boosters themselves are different. Good luck if you get the 1406. Unless the engine is truly dead stock or really close, you may have trouble. If it's really over 9:1 compression it's going to want more than the 1406 I believe.

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Not sure that writeup is factually accurate. I called Edelbrock. 1405 and 1406 have extremely minor differences. Primary and secondary venturies are identical as well as boosters. Primary jets are 0.98 and 1.00 - a 2% difference in flow area. Secondary jets are identical. Metering rod is the same diameter but slightly shorter on the 1405, which makes the carb run leaner. So slightly leaner primary jet on 1406 and slightly leaner metering rod on 1405, which makes both carbs essentially equal out of the box. And for $5, I can change the primary jet on the 1406 to make it identical to the 1405. Or for $75, I can put an electric choke on the 1405. Don't forget at altitude, engines run rich unless jetted down. And just for information, higher compression does not flow more air. Bore and stroke do not change. It still pulls in 318 inches of air per combustion cycle. You still need a 13.8:1 air to fuel ratio - same amount of air and gas.