[Tech @ BG]

Originally Posted by Skip Fix

TECH @BG If my flowbench pulls 10"(or 15", or 28) what factor to get at the 1.5?

OK your Speed Demon 850cfm has 1.562 venturi, and 1.75 butterflies. The Race Demon 1000cfm has the exact same specs. No choke tower, and even if it has thinner throttle blades or downleg different boosters they are NOT going to make a 850 a 1000cfm carb. I can see maybe 50-70 cfm. The same goes for the Holley 850 DP and the 1000 HP carbs-same exact specs, has to be different flow pressures. The same size hole will flow the same cfm unless you change the pressure tested at, at least they do on every flow bench I've used.

My Speed Demon idle screws were almost right on out of the box and it performed well. It picked up 0.3 seconds and idled better over a Carb Shop 800 CFM Q jet even with the adapter to make it fit the intake.

Skip,

As for your first question you would need to either set your flow bench to 20.4” of H2O or mathematically convert from whatever depression you’re flowing at to 20.4” to give you 1.5” Hg. With that being said, dry airflow vs. Wet airflow can make a tremendous difference in CFM number.

I cannot speak for how Holley is rating their carburetors, but as I stated earlier the number or CFM rating on our carburetors is not a direct correlation number off of a flow bench it is an average or median off of engine testing based upon recommended application usage. You are correct, similar size holes will have similar flow numbers when measured on a bench or the same pump (engine).