I have an 86 Iroc with the GM performance parts zz4 swap. (350 with aluminum heads, roller cam etc.) Car has headers/3 inch exhaust from the headers back... I want to know what carburetor I should switch to from the quadrajet. Been running the quadrajet for a while and want to scrap all the smog stuff and get a better carb on there. I do not care about passing a smog/emissions test as I do not need it where I live. Not worried about gas mileage...just power. I've been thinking holley street avenger 670. Any suggestions?? Thank you

Welcome aboard thirdgen.org.

If you have the computer q-jet, you already have the best street/strip carb system available. Not sure why you want to remove "all the smog stuff", but I can tell you that you won't be putting a better carb on. You can (illegally) remove some of the "smog" equipment, but the carb is more than just "smog" equipment - it's as good as you can possible get for street/strip performance (did I already say that? No apologies, it is simply true).

You didn't mention what transmission you have or what else you've done beyond exhaust. If a stock TH700R-4, a higher stall converter would be a better investment than a different carb and distributor.

If you simply and absolutely refuse to take this advice and get something else, don't get a Street Avenger. The reasons Holley offer that thing are all about marketing, not performance. Save yourself some money and grief and get a 650-750 CFM double pumper. You'll need a different distributor as well.

But, if you do that, you won't make any more power. The q-jet has as much or more power capability than any aftermarket carb.

See my vBGarage for details on my ZZ4 clone installation.

I have the stock 5 speed tranny. Not a whole lot of other mods...hypertech made a chip for the computer. The aluminum intake and heads were ported... It just seems as if the car has lost power over time. Haven't really done any looking into it, but it just seems as if slowly the power has decreased and now I'd say it has about 60% of the power it had after all the initial work was done to change it over to the zz4. The ignition system is the stock HEI..with some accel wires. Haven't looked into "re tuning" the carb or checking timing / the ignition side of things...maybe that will be my next step. I was just under the impression I could get more power out of a different carb. I'm brand new to the whole chevy/camaro scene...and especially carbureted cars. The car was actually my uncles and he did the swap himself and put at most 2,000 miles on the new motor. According to him it has lost the power it used to have. When the car was running at its strongest he ran a 13.38et on street tires "spinning the tires through the first three gears" Thanks for any info you can give me....


oh ps. the car also sat for the last 5 years or so in a garage because the fuel pump went out and my uncle did not feel like or have the time to deal with it. I dropped the tank, dumped the gas and changed the pump and got it running again..its runs excellent, just lacking some power

I will grant that with a T5 transmission, a Holley double pumper has a slight advantage when shifting WOT. You will pay for it street driving, though. No other carb should be considered - not an Edelbrock Performer, not a Holley vacuum secondary, etc. Either the q-jet, or a Holley double pumper.

If you do change the carb, you will also have to change the distributor.

Did you change the fuel filter? If you have an in-tank electric pump, there is probably an in-line filter back by the rear axle, and one in the carb inlet.

You really need to get everything else up to snuff before you consider a carb change. Check the timing for sure. If it sat for 5 years, the distributor cap & rotor may need replacing.

thank you for all the info. Any thoughts on what I need to set my timing to? I as well am at 6,000ft elevation. I believe the recommendation for the zz4 was 10 degrees initial and 32 total? Let me know your thoughts. Thanks

The q-jet is an awesome carb if you do the mods on it but im not sure how to make it work without an egr, maybe five7 can chime in. I think a 650 holley double pumper would be the best for that motor though. I'm not a fan of vacuum secondaries (not a good choice for a manual either), I would rather use a carter/eddie than vac. sec carb. holley double pumper would be best, no bigger than 650.

650 would be the smallest you should use, but a 750 DP would be fine on it.

34-36 degrees total mechanical (with the vacuum advance disconnected), 10-12 initial. If you're talking about the computer system, 6-10 degrees base with the EST disconnected.

five7- being I live at 6,000ft elevation (Lake Tahoe, CA) and will drive the car there and take trips to the track in Sacramento which is at sea level...do you recommend I stay with the quadrajet for sake of not having to re tune for optimum performance everytime i leave Tahoe? The car will for sure get driven at various altitudes pretty often...I assume the quadrajet being a feedback carb adjusts where as the double pumper would be set and any adjustments would have to be done manually? Thanks again for the info

That's a big advantage of the computer controls.

It won't adjust idle speed, so that might have to be a compromise, or something adjusted when you're at either extreme. Or, it might not be a problem for you.

Sounds good, I think i'll be staying with the qjet. Another question while I have your attention. How do I disconnect the spark advance while setting timing? I'm familiar with Fords "spout connector" but not sure how to do it on Chevys computer controlled HEI. Thank you

There is a flat 4-wire connector going from the base of the distributor to a firewall harness. Disconnect that, start it up, set the timing, shut it off, plug it back in.