Basically the Rochester Quadrajet does come in 2 sizes , Doug Rowe's book on Rochester carbs will show that. The Quadrajet was used on such a wide range of engine sizes based on its internal bits ,mainly its metering rod and jet sizes. it was used on the Pontiac OHC engine too but GM simply limited the abilility of the back barrels to open 2 between 2/3 and 3/4 of wide open throttle position .
