7t9l82

i agree i have an old swap meets Holley spreadbore on mine and love it. i bought it to be able to rebuild the quadrajet. i bought cliffs book and bought the complete kit from cliff and its bagged up and on the shelf because i have no desire to replace the Holley, best $20 swap meet part ever.

81$$pit

I just did the same on my 81. I had problems and returned the first
Edel, second one did the same thing. I called them and they said it sounds like a heat soak issue. put in a 160 degree stat SAT when it 90 + high humidity, drove about 15 miles no problems, drove to work today 22 miles no problems. I also ordered from Jegs a heat insulator gasket that replaces the carb gasket. Its a little thicker but I think it will still fit. I am going to put it on just for extra insurance.

fauxrs

The problem is often that too many people buy a carb and pop it on out of the box unmodified and this sets their impression of the carb in question. I have run all three of the carbs that have been discussed in this thread.

1>The original Qjet which was very old and never liked my new engine (carb unmodified from the L82 setup)
2>The Holley spreadbore which has been tuned by Lars and later (with new motor) tuned by Jeff Smith of Car Craft - it can get 22mpg on the freeway easy and runs smooth throughout all regimes.
3>Edelbrock emissions carb - which even with some tweaking ran awful.

I bought the edelbrock for emissions reasons and used it for smog tests, took it to a local corvette shop for smog testing and while they got the car passed, their opinion was - get rid of it and bring in the qjet - which they would fix and setup for the new motor.

I did this and the qjet - now properly setup runs as good or better than the holley, and vastly superior to the edelbrock in every respect. also the edelbrock doesnt have enough vacuum ports to hook up all the stupid vacc lines in an emissions setup - requiring additional tees in the lines to make it work.

That may or may not be an issue with some folks who arent worried about emissions testing.

In my experience, each of these carbs works of course, with all three set up for my engine, the Q-jet is slightly superior to the holley spreadbore, both of those are superior to the AFB.

jb78L-82

Well said and always extremely useful when you can relate real world experience to your comments! I looked up your profile for your car (I knew it was not an original L-82 from prior conversations) when you stated the 22 MPG with the Q-jet since I was perplexed. My L-82 4 speed with 3.70 gears couldn't get 22 MPG if it was idling going downhill (LOL) with the Holley 650 spreadbore but does manage 17-18 MPG on the highway, if I drive 65-70MPH, no more than that-3,500 RPM. Sure enough, I see you have a TKO 5 speed which confirms my thoughts about the C3's gas mileage-If you want good mileage you MUST have an overdrive of some sort. I am pretty sure that my OEM L-82 with 3.70 gears and the 650 Holley could get very close to that 22 MPG if I installed a 5 speed with a steep overdrive. Full disclosure: Everything is original internally to the L-82 BUT the 4175 Holley, zero emissions, McJacks shorty headers, 2.5 inch true duals/Monza Turbo Mufflers, K&N airfilter in the OEM dual snorkel cold air intake, comp cams roller rockers, Crane HEI module/Crane adjustable vacuum advance, and a 170-175 operating temp.

billla

Why do these discussions all get so heated?

The Q-Jet is a *great* carb. Being a spreadbore, it provides great off-idle and mid-range throttle response and fuel economy while giving great "oomph" when the secondaries open. Many are very tired, and many have been "tuned" such that they just don't work right any more. A professional rebuild followed with a professional tune will provide great results for even a pretty strong street engine. Finding a professional tuner can be a challenge, especially locally vs. mail order.

As for the aftermarket, it's a bit of a misnomer to compare a square bore to a spread bore carb as they're intended for different purposes. But having said that, I've used both the Performers and the Street Avengers and find that both work well...but I do find the Holley easier to tune. The Edelbrock is very convinient, but I typically can get closer with the Holley. I've been doing a lot more detailed performance tuning over the last year or so and that's kind of changed my opinion towards the Holley. That's just one guy's opinion and experience and means precisely dick

But all of these - working properly and tuned correctly - are going to be within a few percent of each other on power and will all offer good driveability and fuel economy.

fauxrs

Yes the car was originally an L-82 and that was what the q-jet was set up for until recently. Indeed the TKO assists in mileage though I did get as much as 20-21 mpg on the original L-82 4 speed setup, this however was on one tank all freeway long distance driving through fairly flat territory and was never repeated until I got the TKO - now 20-22 is commonplace on the freeway.

The Q-jet has always gotten better mileage than the holley.

jb78L-82

Someone may find this interesting: Just pulled out the owners manual for my 78 L-82 4 speed and the original owner logged the cars gas mileage when it was fairly new (build date October 1977)-totally stock! No reference to the actual driving to get said mileage with the Q-jet-brand new. Here is what is in the operating record (he records miles and how many gallons and the PRICE for the fillup:

August 10, 1978-17.2 MPG
August 12, 1978-18.1
August 17, 1978-17.6
August 21, 1978-16.1
September 17, 1978-16.2

Not too shabby with the Q-Jet for probably mixed driving, a little better than the Holley 4175 Spreadbore, but not by much-maybe 1-1.5 MPG.

a1sensei

If this is a serious request and you have the patience and want to dig in and learn and do the work yourself, PM me and I will walk you through.

God bless, Sensei

noonie

The 75 is the worst of all the qjets, a 1 year only design. It was the first attempt at the super lean carbs and was immediately abandoned that same year. They can run very well and extremely lean on a stock engine, but do yourself a favor and get a 76+up carb to get a lot more tuneability and potential.

rcread

Here's what author Cliff Ruggles said about the Edelbrock carb in another forum.

Clubby99

Much of the problem is that many owners don't know how to tune a Carb properly. They bolt it on and that's it. Of course the carb will run but not at peak performance and best gas mileage. Then the owner is disappointed with their "bad" new carb. I'm not sure which Carb is the best. I'd like to know. I'm tired of hearing everyone state their carb is the best. Has anyone ever seen any independent test data? Maybe a magazine review by an expert?

Maybe a better "expert" than Cliff Ruggles. Duh, even I know a 750 carb is wrong for a 350. Should use a 600 carb. Another example of an "expert" not giving good advice.

billla

While from a strict size perspective that might be true, with a vacuum-secondary carb it's tough to over-carb. With a square-bore, it's more of an issue since the primaries are too big and mixture velocity is lost, but with a spread-bore like the Q-Jet the small primaries give good throttle response and the huge secondaries will only open as much as they're needed - especially if the air valve is adjusted correctly.