What is the difference between an early model Q-Jet and some of the later ones such as the late 70's early 80's models. Some builders will only use the older cores while companies like JET recommend a later model Q-Jet because it is more adjustable? I'm not interested in numbers matching just want to find a core that will perform well and the later model carbs are much easier to find.
To the best of my knowledge, the later year Q-jets just have more emissions controls and vac. ports, so more to plug, more to leak. Jay I did on the other had buy a Stage 2 from Jet, I only had 2 extra vac nipples to plug, and because it is a chevy bowl style I had to re-route the fule line, but otherwise, I am extremely pleased with it.
The short answer is the later carbs HAVE MORE POTENTIAL; IF MODIFIED. The key phrase is "if modified". The long answer is a new book just released entitled "How to Rebuild and Modify Rochester Quadrajet Carburetors". by Cliff Ruggles. Cliff may be reached at (740) 397-2921. My opinion - absolutely the best money you will ever spend on a quadrajet. Jon.
From what I have heard, if you want to run a Quadrajet, the 1972, 800cfm #7042240 is a good place to start. It is what I am working with at the moment. That may change when I put my 550HP motor together, if I cannot find someone local, to help with dyno tuning. That is however, a good year or so away. If you have some specific questions, or needs, I would ask John Osborne, he probably knows as much as anyone in the Buick world. Good luck! Regards, John.
The short answer is that Carbking is correct here. The carbs used in the '75 and later units metered fuel just as well as the earlier versions. They were, however, slightly shorter in height to allow for lower hoods. The metering components were changed slightly to accommodate the different height, but their potential was unchanged. Components used in the later versions were also more tolerant of "modern" fuels, and their availability is better. They can be modified as easily as the older ones, since the technology was typically similar, and the correct modifications make a superior carb to ANYTHING else on the market, at any price. I have successfully remetered Q jets of all vintages, with great success. The only difference might be the electonic units, which require a computer, but their remetering took little more effort.
