[Cliff R]

CID x 2 gets you pretty close for very well thought out engine project.

I've dyno'd all sorts of carbs on 400's and 455's, on quite a few different intakes. At the 500-550hp mark a 455 will want around 850cfm to make the most peak power. Even with that said a 750 powers them just fine, and the numbers will be equal to at least 4400rpm's.

From there on up the larger carb will make a few more HP everyplace.

At the track the differences will not be very much, as a 455 uses it's huge torque production to produce good ET's.

Back to back to back I tested carbs from 750cfm to 850cfm on my last 455 making right around 514hp. The difference from best to worse was less than .15 seconds and 2mph. Interestingly that for some reason a real 1971 HO carb rated at 827cfm ran virtually the exact same ET/MPH as my 1977 Pontiac carb rated at "800" cfm. We also ran a big Holley carb on the same outing, 850DP, and it ran just a tad slower than the 1977 Pontiac carb, .03 seconds and .30mph.

So FWIW it's about a wash at the track at 500 or so HP from 800-850cfm. The smaller 750 Pontiac Ram Air carb we tested ran the same in short times, but slower everyplace on the entire once the car shifted out of low gear, so it netted almost a tenth and half worst et and almost 2mph slower........Cliff

[jonmachota78]

How much does an annular 850 flow? Assuming the annular boosters are a restriction?
This question seems on topic