Is there much difference between OEM Quadrajets?

[Tunerz]

I've rebuilt a carb or two in my time, so I'm not completely thick. But my question stems from looking at Quadrajets on ebay. There are several that are going for next to nothing, and I have absolutely zero belief that they are in running condition. However I don't mind rebuilding them.
My question is simply can a quadrajet from say...uh... an 91 350 gmc sierra be bolted to the intake of a 68-72 350 buick. Do the bolt patterns actually differ or are they standard between GM's of any year (ignoring thermoquads and any other computer ones). It doesn't take rocket science to know that the cfm's, jets, chokes and vaccum assemblies (which could be rerouted or blocked) would be different. And should the throttle linkage be different, I'll simply cutt off the one from my 2 barrel and weld it. Nothing new for me there.

Finally, assuming they are indeed application specific, are there any carbs for Olds or Pontiacs and of what years, that I can use on my 350?
I'm asking since I'm have that urge again to tear down a carb and rebuild it better..... maybe it's a youth/stupidity thing. :Brow:
Thanks in advance
Tyler

[Nicholas Sloop]

Yes and no...
All have the same bolt pattern, so, if willing to go to extremes (like welding on a throttle bracket), thay can all potentially interchange.
The diameter of internal passages will vary according to original application, so a later emissions carb off a small block will not run well on a big block.
Personally, I would hold out for a 68-74 Buick 350 carb. They show up often enough.

[Tunerz]

I think I'll take your advice and wait it out.
Many thanks.

[Schurkey]

There are so many different castings for Q-Jets that things could get VERY interesting VERY quickly. Basically, you could take any two Q-jets at random and not have much of ANYTHING that would interchange.

That said, if you know carbs well enough, and have facilities for testing them, you could get a proper fuel curve from nearly any Q-jet. It would take years of experience to get to that level, though.

If you have a donor carb with the proper throttle lever, I'd just switch the whole throttle lever when you have it out to re-bush the throttle body. No reason to weld a new throttle lever to an old throttle shaft.

[Tunerz]

Unfortunately while I some experience with carbs, it's diffently not that much! And I'm not sure if there are any decent place to test out the carb locally, if even in the province! Assuming the throttle shaft is the same bore between the 2bbl and 4bbl, I see no problem with interchanging them. However with my luck lately I'll be firing up the MIG, even if I pickup the proper carb.

Thanks for the info.

[Nicholas Sloop]

Assuming the throttle shaft is the same bore between the 2bbl and 4bbl, I see no problem with interchanging them.


No dice on that one. Not even close. The bore for the shaft may be the same, but its length and the size/placement of the throtle plates will be way different.

[Tunerz]

The thought crossed my mind but I was to tired to think of the technical names for them, but yes your right, the primary bores could differ considerably. Well... I'll just keep watching ebay for a busted up buick quadrajet and hope for the best.
Thanks for the tip