What CFM

Just pulled the Quadrajet off a Buick 455 I bought last year. Its a 7040257, which decodes to a 70 Olds 455, possibly from a 442.

Anyone know the cfm rating offhand?

Any input on using this one vs. a Buick-delivered carb?

 

From memory...my friend's '72 442 had a 750. Maybe the '70's used a different cfm rating for no emission controls.


On a Buick engine, the stock carb for a 455 from 1970 is an "800" (I think it is actually 795cfm though), and it's generally agreed that the engine is probably undercarbed from the factory.

Also, I would question whether or not the choke is correct for the Buick engine. I'm not knowledgable about the different choke setups from GM enough to say yes or no it will be fine with the Olds choke setup, but I can see a situation in which a problem might occur with the choke.

Personally, I ran a 750 cfm carb on my 455 for years and it ran fine. Probably cost me a few hp more than I realised though

 

Thanks Chris

I'm hoping for an 800. If not, I may just swap it onto my truck. It shouldn't need as much carb since I don't run it as hard.

The choke stuff is all missing anyway, so whether its right or not doesn't make much difference. :laugh: A friend of mine wants to try cross-breeding it with the electric choke parts off a later carb. I didn't know there even were electric choke versions of the Quadrajet, so that's completely up to him. It'd be nice if he could make it work though (my crossover's blocked).

 

Minor point of correction. The '70 455 carb was a 750. In '71 and '72 the bigger carb was employed.

 

Thanks brad:TU:

 

I don't get it. Or, I don't see it for that matter. I have what by the numbers is an 800 cfm quadrajet. Yet EVERY quadrajet I have looks identical. They all have the bump shown in that picture. Heck, even my one retarded 80s computer quad looks like that inside. What the heck?

 

Dan, do you see the little bump/bubble in the 3rd venturi on the picture? The 750's don't have this. I've got a bunch of carbs laying around here...I'll see if I can shoot a couple difference pics real quick.

 

I lied...I don;t have any 750's here. I do believe that after a certain year, they all had the big venturi's like the one pictured above..

 

Dan, maybe sometime I'll show you my Q-jet from a 70 Riv. It doesn't have that bump.

I'll try to explain what a 750 looks like: If you were to take the bump in the picture above, and then add material the circumferance of the bore, the same distance of the outermost part of the bump. You would then have a 750. I think the material was taken away to make an 800 cfm. The bump may have been left because of some circuit that would be exposed if it where taken away. Hope that did it!

Anyway, give me a buzz or call my brother. Between the two of us you'll get to see the carb. It isn't being used right now because it has the devil in it. Should have never rebuilt it. It was running fine before.

 

Sorry guys. I keep checking every quad I can find. Including the stocker on my 69 Wildcat. The "Bump" is on every one of them.

 

Dan, this pic shows the difference between the 750 and 800 a little better.

 

Thanks Kevin!

Now I see.