The Stovebolt Site Forums The Shop Area Engine Shop Q-Jet on a 283

I've never done a carb/intake manifold swap before and was told that I'd have to "jet down" this four barrel Rochester since my engine, the original 283, has a 2 barrel Rochester. Is this true? A member of another forum that I am part of said something about the carb being advanced enought to adjust for the engine it was atop of. Something about the weighted flap on top or something. I've been unsuccessful in getting a reponce from him since. Anyway, is there any truth to that and if not other than trial and error how would I go about getting the correct jets to "jet it down." Also, did these engines ever have a four barrel offered in 1966? Is so could I jet go get those jets?

283's as often came w/ the 4 barrel as w/ the 2 thru their whole production run, depending on the application, and the one you pick up will likely work fine once you get things adjusted

Bill

I pulled an original 4bbl intake off the 283 that I just rebuilt. I put a new intake on the rebuild but I had the old one cleaned up & squared away by the machine shop. It's like new & ready to go. If you need one, let me know.

P.S. It had a Holley 650 on it with the jets in it that come with the carb at purchase. It was on there for many years & the engine seemed to handle it just fine.

The 283's never had Q-jet carbs, because they hadn't been invented yet. It's a great carburetor, but you will definitely need to do some rejetting. The jets will need to be richer, not leaner, however, and the float level will need to be set a little higher. Small-displacement engines develop less venturi vacuum, because they're flowing less air volume at any particular RPM, so the jets need to be larger. Get a set of numbered drill bits, and start increasint the main jet size a few thousandths at a time until the throttle response and power suits you. A flow bench and a chassis dyno will help a lot during your experimentation, if you happen to have those items. Otherwise, it's all "cut and try" work. I've seen a .005" change in jet size get a 20 HP increase during a dyno run.

A Quadrajet calibrated for a 305 engine will be pretty close to the jet sizes you need for the 283, and might work OK with just a higher float level setting. You will probably need to tighten the air valve spring a little to prevent bogging when the secondary throttles open, also. I'd try that approach first.
Jerry

I agree with HRL. The Q-jet is a great carb for driveability & fuel mileage. One from a 305 should work just right. It is easy to adjust the secondary air valve to match your engine. They are a dime a dozen at swap meets but you will have to put a kit it. Look for one from the late 70s to early 80s with the round choke without the electronic engine controls. If it doesn,t have an electric choke you can put an electric choke coil on it.

I have a put 3 different q jets on my 283 that I rebuilt. I run a turbo 350. Teh first one I got from the parts store and just asked for a carb for a 67 chevrolet 283 which is what it came from. It worked great. It got filled with tank crud recently. I replaced the tank and put one on that had manual linkeage. It worked great. I had a friend give me one with automatic linkeage. It worked even better. I think they are pretty forgiving.

As I was digging thru the shop manual for my 58, I stumbled across a maintenance entry for the 4bbl Rochesters. So FWIW, they were available as early as 1958 on the 283 engine.

4-BBL carbs have been available as far back as the first V-8's, but the Quadrajet didn't appear until 1966. The first Chevy engine equipped with a Q-jet was the 1966 Caprice 396, I believe, with most GM engines using them by 67. The previous 4-barrels were either Rochester 4GC's, or Carter WCFB's. The early models are a pain in the butt to work with, especially the 4GC!
Jerry

Just need to throw in my two cents on the Q-jet discussion. When they work, I love 'em. When they don't, they're about as difficult to tune as anything. They're pretty much meant to be tuned from the factory. If you go to the parts store and ask for one for a 4.3L v-6 (85-86 monte carlo) it will be 500 cfm, rather than 785 cfm, which is the next size up. The 4.3 is 262 cid, so it should pretty closely match the 283's needs

HRL - my bad. I read the original post without paying enuff attention to the topic header. Thought he might have been using the terms interchangably.

I'll just go re-jet my cerebellum now!