I am looking for some basic advice on which way to go. I am an extreme novice with all things mechanics. (I am a computer type person lol) I really on friends to help me with such things.

I have a 1978 L48 Coupe and as the story goes, is a barn find that was sitting since about 1987ish to 2010. There has been a lot of things done little by little.

My current problem is that the Q-Jet Carburetor has been recently declared un-salvageable (It had been "running" until recently). Oddly enough it appears it had been a 1975 model Carburetor also. Now I am left with a choice I am not educated in making. The local corvette shop's trusted rebuilts are sold out currently. That leaves me with the choice of getting something else. I know that Advance has something from United who I have no idea there quality, or maybe an aftermarket Holley in which I have no idea the difficultly of proper fit or appropriate models. I am told that Holley makes a direct Q-Jet replacement but I am not sure were to look for this or what the model is. I would like to stay at or above the performance of the stock Q-Jet at the very least.

So.... I figured I would ask everyones experience of what they are happy with for replacement carbs. What has worked well for you? What would you recommend? What would you put on your car? Thanks in advance.

 

Whatever you get, stay 650 CFM. No higher. You don't want to over-carb your engine and that L48 doesn't need more than what the Q-Jet would put out.

Q-Jets were everywhere. You can get them off old Chevelles, Monte Carlos, Novas, or just about anything else Chevy put a 350 on in the early to mid 70s...

If you go Holley, I'm pretty sure you can bolt a Holley on pretty easily, but don't get all happy with the Holley and throw on a 750 double-pumper or something because all you'll do is flood your engine and choke things up with unburnt gas. That's REALLY BAD for your exhaust system - you'll go through exhaust systems much more quickly - and your car will run like crap.

If you can't get a Q-Jet and don't want to go Holley, you can also go Edelbrock, or any of the other big names. Just about anything will bolt to a 350. You shouldn't even have to change the intake manifold.

On the other hand, once you decide to go 'non-stock' you might consider a new intake manifold (Edelbrok Performer series maybe) and if you want to really unleash your engine get some nice heads (I've always been fond of Merlin Dart IIs) and a decent Competition or Crane cam - sized for your new heads.

But even if you do all that - STAY AWAY FROM THOSE 750 CFM CARBS!!! It's amazing how many people over-carb an engine. Your carb needs to be the right size - with the right jets too. 750 CFM even jetted correctly is still a bit too big for a 350...

 

Q-J or Holley replacement will bolt on stock intake.

You don't really need to be concerned w/ what we would do, anyway I put an al. intake w/ Holley & change heads & cam minimum.

 

All Q-Jets are at least 750 cfm. I would would buy a Quadrajet on ebay and then have it rebuilt. I did this with the carbs on my '72 LeMans, '78 Firebird and am rebuilding the Q-Jet on my '71 Corvette myself.

 

I don't know about all Q-Jets, but I've never had a 750. Only 650s. And I've had several.

 

No such thing as a 650 cfm Qjet. They are all 750 or 800 cfm.

 

I stand corrected! All Q-Jets were 'capable' of 750 CFM though they weren't always used as 750s. I never knew that!

 

The Q-J has small primarys & sizes itself to the engine so the Q-J rating is not relevant here as wgarneau is saying don't get a squarebore 750 as in a squarebore only 600-650 is needed.

 

Nor do I know how you can apply a 750 as a 650...

 

Thank you for the explanation!

 

I purchased a Q-Jet replacement from Sean Murphy Induction in California and it works perfectly. It was around $300 and had a good warranty. I recommend them.

Dan

 

if you are looking for a place to look for a replacement, the guys at jegs and summit are really good with help. i would also check in with the folks at wilcox one of the forum sponsors to see what they might have.

 

Thanks for that. I emailed him. We will see what happens.

 

What about the secondaries? Do you put the vacuum system back or opt for mechanical secondaries?

 

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It runs as good as it looks, electric choke which always works.

Sean Murphy,
http://www.smicarburetor.com/

Or Cliff,
http://www.cliffshighperformance.com/

Vacuum secondaries on stock engines.

 

If it's vacuum stay that way - and particularly with a carb that matches it's size to your needs. You do nor want to over-carb your engine.

 

The Q-Jet is a 'demand' type carb. It may have a max capacity of 750 or 800 cfm, but the carb secondaries only open up as much as needed by the engine to which it is mounted. It doesn't get matched by cfm to an engine like a Holley. For those, you need to have a carb that has enough flow capacity for your engine...but not much more.

For both carbs, the rods and jets need to be sized for good A/F mixture and good performance.

By the way, who declared your present Q-Jet as unrepairable??? If it was a repair shop which sells carbs, hmmm.... There is nothing on a Q-jet that can't be repaired and/or replaced. A good quality rebuild kit, a new brass float, new viton needle valve/seat, and proper rods, jets and tuning will make your present carb work like new. Yes, it's possible that your throttle shafts could be worn and leak some air...but it would have to be worn pretty badly to make a significant dent in its operation. And, since the carb is a '75 or later vintage, it's unlikely that the plugs in the bottom are leakers. I just think you need to get a "second opinion" on the viability of your present carb...from someone who is unbiased and who knows something about Q-Jets.