I purchased a new Q-Jet carb. for my 1979 305 elcamino and now I change out the engine for a 350 300 hp out of a 69 Camaro will the Q-JET still work and not take away power
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I purchased a new Q-Jet carb. for my 1979 305 elcamino and now I change out the engine for a 350 300 hp out of a 69 Camaro will the Q-JET still work and not take away power
Quote:
Originally Posted by 1979chevyss
Properly set up the Quadrajet will out perform any other carb on a basically stock sbc
I will get corrected if I'm wrong, but I think most quads are jets are good for 750 CFM. Like Ken said proper tuning is key, the problem is there's fewer and fewer people including me that know how to do that
I have not worked very much with the Quadra-jet carbs, however I seem to remember they tune similarly to the Edelbrocks, with some variations such as the secondary rods for additional WOT fuel.
Here is a link to an articles about tuning the Quadra-jet;
http://www.northstarchevelles.com/No...ning_Paper.pdf
Quote:
Originally Posted by 36 sedan
The folks on the Corvette Forum consider Lars to be the guru as it pertains to Quadrajets and once I get a few things sorted out on my 76 Corvette I am going to send him my QJet for a rebuild.
I really just need to know if there is a difference in quad for 69 to 79 because 79 had a lot of pollution and I was wondering if the 79 carb. due to that fact would reduce power
Quote:
Originally Posted by 1979chevyss
I don't believe so. The electronic controlled carbs were sometime around 82 IIRC and if I'm wrong someone will correct me. The one thing I'd do is to run an electric choke. I believe this is the one I'm using on my 76 Corvette. https://www.ebay.com/itm/Rochester-E...kAAOSwkvtb43DZ
There may be some power to be gained from rejetting the 79 Q-jet. The 79 engines had EGR and the mixtures jetting tended to be leaner due to the exhaust gas diluting the incoming A/F mix. Otherwise, your carb should be more than adequate for your new engine,
I have tuned a few Q-jets and find them to be great street carbs. When well tuned, they can give mileage numbers approaching those of EFI. I probably wouldn't drag race one unless I was limited by the rules because they are difficult to rejet at the track.
They were made in 750 and 800 (850?) CFM ratings, although some were limited in the secondary linkage to open less for smaller engines.
BTW - You didn't ask, but I will add that a properly setup Q-jet will NOT bog when the throttle is opened. When the secondaries are set up right, the carb's air valve will just open as the engine can take the flow. The seat-of-the-pants feeling is just a continuous building of power.
A Quadrajet is an excellent carburetor for a mild to moderate street engine.
There are a couple important things that need to be done to it.
One, you need to adjust the opening rate of the secondary air valve. From the factory, they usually take 4-5 seconds to open. For best performance, you want yours to open in about 1-2 seconds. To rest it, connect a Mityvac vacuum pump to the secondary air canister. Apply about 15 inches of vacuum. Release the vacuum and use a stop watch to see how long it takes for the canister to extend all the way. There is a metered orifice at the vacuum hose inlet to the canister. To adjust the opening rate, drill out the orifice with a 1/8 inch drill bit. Next, take a wooden or plastic golf tee, and cut the head off it. You will drill a small hole through the golf tee, and slide it inside the vacuum hose between the canister and the manifold vacuum source. You can try using different drill sizes until you get the opening rate that you want. I think I ended up using about a .055” drill bit with mine, I can’t remember exactly. Doing this will eliminate the famous Quadrajet “bog” that so many people complain about.
The other important thing to do is to adjust how far the primary metering rods are inserted into the jets during cruise conditions. Late 70’s Quadrajets are the best ones to have, as this is a pretty simple adjustment on them. There is a plug from the factory that you have to remove in the top of the carburetor. This plug is directly over the power valve/primary metering rods plunger. Tap out this hole so you can install a 1/8” pipe plug in it later. Warm up the engine, and run it at cruise RPM, say about 2800 RPM. You can stick an adjustment tool down through the hole and turn the APT (adjustable part throttle) screw until you get the smoothest running and highest RPM. Now the cruise mixture is set correctly for your engine combination. This will likely be richer than it was set from the factory for the smog engine.
There are plenty of other little adjustment you can do to fine tune a Quadrajet, but starting out with these two will get you very close. I use a Quadrajet on my Chevy 350 T Bucket, and the throttle response is fantastic. It just takes some patience and experimenting to get it right.