Magna86

OK I'm looking to find a few good Q-jet cores for rebuild to use on future 455 engine builds. I've found enough info to identify most of them and will be ordering a Q-jet book for tips/tricks to rebuilding. What Q-jet carbs are the ones I want to stay away from? Is it during certain years say 74-77 when smog worries was killing everything? What are the thoughts about the 77-79 "800cfm" carbs that were used on the Trans Ams? The 66 has one of those and it runs great so was thinking of locating a few of those. I'm not worried about correct as both vehicles are mutts. Also any issues running a Q-jet on a performer or performer RPM intake? Any help is appreciated.

TripDeuces

Personally I have a 66 Q-Jet and want to smash it some days. These are the first Gen models and can be a nightmare. These are the ones with the first gen fuel inlet. I'm reluctant to call it a needle and seat as it's an oddball type thing. Rebuild kits for these actually replace it with a conventional type unit but you still can have problems with the two attachment screws that hold it down. The other major problem is the small tower that connects to the fuel inlet passage on the passenger side inside the bowl. Don't know what the original plan for this was but it is plugged and is notorious for leaking, even if plugged. For your own sanity I'd steer clear of them. If I'm not mistaken the 67 models were modified and don't have these issues.

henryk8398

Avoid any carb that has two electrical connectors on the front. Those require the computer system to work. They were made from 1981 to 1990 (some 1980 models in CA had them, too). In my opinion, the carbs from 1973 to about 1980 are calibrated lean. I don't think a healthy 455 will be very happy with it in stock form. That's the dark days of the smog era. HOWEVER, they are a great basis to start from and can be modified to work well. In addition, they can be converted to electric chokes and also have the the adjustable part throttle system from 1975 on. The 77-79 403 carbs are great, but again might be too lean for your application. I bolted one onto a Pontiac 400 and I wasn't happy. It was down on power and ran a little hot. It definitely needed larger jets, etc. Your edelbrock should accomodate both square bore (e.g. Holleys) and Spreadbore (Q-Jet) carbs. If the carb wasn't right for the intake, you'd know!

I strongly suggest you pick up these books if you are serious about a Q-Jet:

http://www.cliffshighperformance.com/buy_book_2.html

http://www.amazon.com/Rochester-Carb.../dp/0895863014

brown7373

I would start with a Q-jet made for a 455 or high performance 400. While you can change the jets and rods to get the mixture you want, the bigger engine carbs had idle circuits made for the bigger engine. Yes. you can modify idle circuits, but unless you know what you are doing, or pay someone who does, you could have problems.

pogo69

I would look for a big block carb from 68-72 this is easy to find on the internet as some sites list the carb numbers for different models.
you should be more concerned about getting a good core that is not cracked,warped or damaged, a lot of carbs get to worn out to make good cores but they may look fine

MX442

If you're going to buy a book, get the one by Cliff Ruggles. In there he will show you how to modify the idle circuits for bigger engines with more cam and less vacuum. Contrary to an above post ^, it does not matter what application you get (ie big block vs small block). Yes, each application is different, but once you understand the "why", it won't matter. A quadrajet CFM is like an air valve. Yes, it will flow up to 800cfm. But, it is variable. It flows what it needs. It is probably a good idea to avoid the 75-76 smog carbs. I like the 77-79 because of the better ATP tuning. Chevy carbs have the right pointing fuel inlet, and the BOPC's have forward pointing fuel inlet. When looking for a core, make sure the fuel inlet is not stripped. It is easier to find one with good threads vs. repairing it. The Olds carbs will already be set up with a compatible throttle linkage. Another excellent upgrade is an electric choke.

With that said, I have a 1979 Olds carb core that I'd let go for $65.

Seff

I agree, first gen carbs are generally not as easy to work with, and the 76 carb has a dual ATP setup or two power pistons or some other voodoo business that did nobody any good, ever. The big bad Qjet Guru Cliff Ruggles runs a 77-79 Qjet because of the ATP tuning potential and the beefier castings.

Octania

The later the better up thru the pre-electronic era is what I hear for a summary.

1966's had an arm over the top for secondary damping- PITA, improved by 1967.

77-79 Olds is your best bet. I am pretty happy with the one I have on the 403 From Hell.

pogo69

yes...true but the BB carb should have rods, jets,pump, needles etc already suited to the big block... if you plan on a total rebuild and money doesn't matter than your options are increased

MX442

I'll agree with that to a certain. However if we're talking strictly 77-79 carbs, was there a BB or performance application in 77-79? I don't think so.

In that case, when you rebuild a 77-79 carb you will need different jets, new pump and spring, new oversized needle, and different secondary rods and hangars. If you call Ruggles, he sells modified primary rods tapered to work well with late model ATP, large needle, and can tell you what jets, secondary rods, and hangar you need. One stop shopping...

pogo69

ok...that makes sense

Magna86

Thanks for the help guys. MX442 I'll be interested in that carb core.

MX442

Magna, I'm leaving town. Early next week, I'll dig it out and get detailed pictures for you.

Redog

Love them or hate them. I've never heard anybody say they are alright, okay or anything else that suggests "middle of the road"

ls98

http://www.oldcarmanualproject.com/m...QJet/index.htm