What Cfm?

[Mcgwirejh]

Hey I have a Rochester 4 barrel carb the number on it is #17084226 I'm trying to find out what cfm it is does anybody know.

[NeCrOmAnCeR]

I can help decode the data # for you. 1984, 49 state emissions, used on Chevys with an Automatic transmission.

Appears to have come off of a truck. Edelbrock lists the 795 CFM for the replacement carb.

[swervin ervin]

All stock Rochester and Carter Q-jets came in two different cfm sizes, 750 and 800. The 800 cfm Q-jets were used on the big inch Caddy engines. So, it's 750 cfm. But, GM sometimes used a little trick to reduce the cfm on smaller engines. They controlled how far the secondary air valve was able to open. If this valve will open all the way to 90 degrees, it will be able to use the whole 750. I don't think any of our trucks had this limitation, my 226 Q-jet didn't.

Also, your engine will only use any of the 750 it can handle. The vacuum operated secondaries will open as far as what is needed by the engine. Sort of like a giant vacuum pump. The bigger the engine, the more pull it had on the valve, so the farther it would open. This is the way these things worked on engines from 305's on up to 454's. Of course jetting and rod sizes would be different too.

[mike reeh]

three cheers for the quadrajet