Goliardi

Was the original Q-jet on a 72 Cutlass 4 barrel 350 the same what would come on a 72 Cutlass 455? And does this pic look like a 750 Q-jet?

Fun71

Check the number stamped on the drivers side behind the throttle linkage. That will give the year and application.

Goliardi

Will the numbers on the side indicate the CFM?

Octania

Yes, to an extent. The carb major pieces were the same or same-ish, with tailoring such as the exact jets, needles, power piston spring, and adjustments making the difference.

Pretty much all of them were 750's

Yes, with some research, the application number will tell if a given carb is 850 cfm. It's MUCH easier to just look in the carb for the telltale bump. I will bet that there are certain main body casting numbers that have the 800 CFM venturis also.

Do a web search on how to spot the 800 vs. 750, there are pictures.

PS I recently acquired a core 800 CFM from a 77 Pontiac 400 engine if that interests you. It's on epay, at an inflated price to cover their costs. I can sell it for much less outside that venue.

http://www.ebay.com/itm/151306284875...84.m1555.l2649

Goliardi

So, my original 350 Q-jet is just about as good for a 455 as a rebuilt 455 Q-jet? I ASSumed the 350 would be considerably smaller (550 cfm).

MDchanic

All QuadraJets up to about '73 or '74 used the same basic castings, with some variations in drilled passages, vacuum ports, jets and needles, and were capable of about 750 CFM, as Chris said. After that, some had slightly larger venturis and were capable of 800 CFM. These have slight bumps or projections into the primary venturis from the outside edges.

If you look up the number on your carburetor, you can find out what its specifications are (provided it hasn't been butchered at some point).

In the sixties through early seventies, there was only one basic casting used for all engines, the nominal 750 CFM casting.
Because of the QuadraJet's secondary air valve metering system, the carburetor will only supply the amount of air that is actually needed by the engine, so a separate smaller carburetor wasn't needed.

- Eric

joe_padavano

You ***-U-MEd incorrectly. It's the same carb, same castings. The reason why the Qjet is such a great street carb is that is is extremely flexible and adaptable. Two features in particular allow it to support a wide range of engine sizes. First is the triple venturies on the primary side. This maximizes the signal, improving atomization for all engines. Second is the secondary air valves, which are opened by mass air flow through the secondaries. The basic carb may be 750 CFM, but flow is automatically restricted to only what the engine needs.

Goliardi

That explains it. The new rebuilt one I purchased did not operate properly, so we took the old one off the 350 and put it on the new 455 and have been amazed at how well the old girl is performing. Thank-you gentlemen. Now if we can just get it finished for some good summer driving.