So I have a guru do up my Q-jet and I'm showing it to my parts guy. In the conversation I mention that it is an 800 and the dude corrects me and tells me it is a 750 because they only made 750 Q-jets. I tell the guy "it's an 800" and he sticks to his guns. After a couple of back and forths, he says "it is right in 'How to Hotrod a Small Block Chevy' and he says "Smokey Yunick says that they only made 750's" I said that he is wrong and so is Smokey. I let it go there and forgot about it. Come to find out he is running his mouth about it, so now I HAVE to show him. I need some sort of documentation that I can download or a book I can show him or something. I need a few sources so there is no question about it. I know they made both and so do you, but I have to show this dude. Where can I find info. that spells it out? I pointed out the ring to him already, but my word clearly isn't good enough. I know this is stupid, but we all know how loud mouthed know it all parts guys can be and he's trying to junk my rep. Please help if you can!! BTW, my carb is a '75 off an Electra, it's an 800 thank you very much!! Thanks, Randy
From Rochester Carburetors by Doug Roe, page 124, column 3. BTW, the difference is in the primary side of the carburetor. The outer venturi on an 800 CFM Q-jet is 1/8" larger than the 750 Q-jets (1 7/32" vs 1 3/32") They are jetted richer because of this. Notice the specs for the 455 carburetors from 72 (Large Venturi and corresponding jetting) This table is from the 1972 Buick Chassis manual. Finally, this picture shows how to ID an 800. The outer venturi has a bump in the wall to clear an internal passage way, see here: http://www.v8buick.com/attachment.php?attachmentid=29696&d=1091748888
Shamelessly STOLEN from a post on this very web site about two years ago. I don't know the origin of this photo--or who to credit; but I've got it on a server now.
Thank You Larry and Thank You Schurkey!!! So I go check my book and there it is on pg. 124. I knew I had read it in that book, but I could not find it. Good data and pics. I'm gonna go get him now!!! :blast: Chevy Guy!! Thanks again, Randy
I thought all q-jets were 800cfm.... (actually 795* cfm...) I had heard about the 750, but i thought they were only produced for a few mystical years and discontinued shortly after. At least thats the way ive been told it was for Chevy.
My understanding--and that may be incomplete--is that ALL Q-Jets up to '71 were 750s. Big Block Buick; and some other big blocks went to 800s; small blocks stayed with 750s through '74. Beginning in '75, FRONT FUEL INLET Q-Jets were all 800s; side inlet Q-Jets could be either 750 or 800 depending on application. Edelbrock marketed an 850 Q-Jet; best I can tell it's an 800 with optimistic advertising.
Here's One Other Thing. To Limit Cfm On Many Quadrajets The Secondary Air Valve (top Flapper) Has A Mechanical Stop On The End Of The Shaft. Although This Tang Is Easily Clipped To Allow Full Opening. Many Went Out The Door Restricted.
Here is another monkey wrench in all this. 73 SD 455 Trans Am carb was 850 cfm. It is in the New Rochester Carb book. I forget who wrote it?
Turns-out my parts guy has alot to learne about Q-jets. Worry not, I'm about to fix him. I'm not too crazy about the way he looks down his nose at my car anyhow!!!! Thanks for the input from all you guys! Randy
That's why I like my parts guy. He only gives his opinion when I ask for it, and it's usually good.:3gears:
