[57Chevyman]

How can I determine the size of my Rochester Quadrajet?

[liquid_larry]

The only way I know is to use the carb # off the side of the float bowl,that will tell you what it was used on from tere you should be able to find the cfm.

[Tom]

I don't know how true this is but I have always believed all Q jets were 715cfm and the way GM increased cfm was through the air horn and different air cleaners and the spacers they used along with different jetting

[Roy Newton- exprotech]

Q jet carbs for the most part 725 CFM there were some 800 CFM but they were all on Hi Perf engines and you can't find one now. I have a book of #s if you want to be sure. I use to race Q Jets and must have 50 Jet and metering rods for front and rear need some? ROY

[cooterks]

This may be a day late and a dollar short, but there is a sure fire way to tell what size your rochester Q jet is. For starters, there were only 2 sizes- 750 and 800 cfm. This is determined by measuring the main venturies: 1-3/32 = 750 cfm and 1-7/32 = 800 cfm. I got this out of the Haynes Rochester Carb manual page 8-2