Would a 4bl q-jet off a 1966 330 be the same as a 4bl q-jet off a 1972 350,or do i need to know the numbers off them.Thanks

 

No. They would not be the same. A 1966 Oldsmobile 330 employed a divorced choke (choke sat to the side of the carburetor itself) 4MV (7026254) carburetor, the 1972 Oldsmobile 350 employed a hot air (attached to carburetor) 4MC (7042250) carburetor.

 

they are similar but not identical.. look at the list here, you will see they are jetted differently. Also read from Cliff's High Performance forum and book that first year 1966 Quadrajets were troublesome. Over the years they got better.. Late 70s ones before electronic Quadrajet got most of the kinks worked out.. Tuning to your specific application, i.e Cam, Compression Ratio, Displacement, Timing, etc etc all play into it. One can't expect to just throw parts at it and have it run good. I see a lot of new people to the group buy tons race car parts and again just expect it to be a screaming monster in the end... Requires tuning...

For the most part stock parts worked pretty well and had to to work in various climates, various speeds, etc most of the time it worked well. GM spend millions of dollars in research to make sure they did..

Fred


https://oldsjunction.classicoldsmobi...sfaq/ofcrb.htm

 

The 1966 Qjets had a lot of one-year-only parts that ended up being problematic and changed in subsequent years. These include the goofy inlet valve, the fuel-damped secondary throttle valves, and the fire starter plug at the fuel inlet. Also, the 1966-67 Olds Qjets used a Chevy-style side inlet, the 68-up use the more traditional front inlet (which also cured the leaking casting plug at the inlet). 68-later Qjets have spun-in aluminum well plugs that fixed the leaking well plug problem that has been (incorrectly) blamed for every Qjet problem. And most importantly, EVERY SINGLE Qjet is specifically calibrated for a particular year and engine. Yeah, they are pretty forgiving (I have a 350 carb on a 454 Chevy truck and it runs) but there's a reason why GM spent the effort to calibrate each one for each engine.

 

They definitely ended up like that but not quite in the beginning. When they first came out on the Olds V8's they were not calibrated differently between some engines. For example, the 400 and the 425 (when equipped with a 4MV) both took the same exact carb with identical calibrations (the 7026250). You can see evidence of this when you see that the throttle linkage is easily swap-able on the '66 4MV as it's different if you have a Toronado or one for another Olds (the throttle arm simply un-bolts). I verified the measurements (idle restrictions, up and low air bleeds, idle discharge holes, etc) through two independent sources.

I have a suspicion that Rochester had the idea at first that they could use just about the same Qjet on multiple engines but realized quickly that it wasn't going to work and started tailoring them specifically to the application within the first couple of years. It seems like about 1967 was when the part numbers really started to diversify for the application.

I still consider myself a newbie to all this and I'm really interested in the early Qjets, despite their flaws, and have done a ton of research on them. Curiously, I've yet to come across a 1966 Olds V8, outside of the Toronado, that actually has the original 7026250 Q-jet on the engine. I'm sure they're out there, I just haven't seen it yet.