I wish I could find a Carter AFB that would fit the stock intake. Never had much luck with the Quad and now with this wonderful car having one as stock equipment I replaced the original leaking sieve with one new that came with the car. It works ok bur takes forever for the choke to come down. Carter and Holley replacements that fit the original linkage and breather???? would be a dream.

 

Q-Jets have been called many names over the years, and beeing out of production for years now, tuning parts are getting harder to find. While Holley and Carter parts are easier to find, bettin' you'll be looking at distant fading tail lights of well set up Q-Jet car on the street.

 

A quadrajunk reminds me of a 4 ft tall basketball player who can make every shot, until the other players get on the floor!

 

I use the Holley 4175 650 CFM vacuum secondary Spreadbore replacement on my 78 L-82 4 Speed and have since 1985-works great!

http://www.summitracing.com/parts/HLY-0-80555C/

 

i use the double Pumper version of the Holley and it is great and i haven't seen any taillights. as mentioned the quad went out of production years ago and tuning parts are harder to find. no body has been able to make one that works out of the box.

 

The namecalling comes because many who have them cannot tune them properly and/ or do not understand how they operate. Now with the availibility of tuning parts practically non existant adds to the frustration of these owners. The Qjet is a very reliable mechanical secondary carb if properly set up and tuned.

 

complainers just can't tune a Q-jet or don't even try, will take a Q over holleys which leak any day and can kick a holleys *** same car with q jet...been there done that back in the day for all you youngster's

 

There are reputable carb shops that still have decent kits to rebuild the Q-jet. Had mine redone and bushed by local corvette shop.

Runs perfect on my 70 350/350.

I long time ago discovered that you also need to make sure all other ignition components are working properly since any bad components can look like a carb problem when in fact it is ignition related.


Bill

 

A properly tuned Qjet will give you slightly better gas mileage, if you can ever get it tuned! Thats it! Eqiv Holley will out perform Qjet everytime, unless you talking about an l-48, and even then you just wont tell the difference. ..again assuming the Qjet is properly tuned, which is doubtful!

OP: Go with the Holley 4175 and be done with your problems!

 

This is a lie.

 

Funny how carbs are. Some claim the edelbrock remake of the carter AFB is junk yet the majority of cars i see now have them running on there street oriented cars some of them even show up with two of them on there cars. If there nothing but junk how can this be. If they were junk people would simply go buy a new holley or about the other seven companies making there version of the holley. If there is a market for something companies will make it. No one even makes a remake of the Q-jet or i guess even hardly any parts for it. So i can't fiqure out why if the Q-jet is both the great fuel milage and performance carb claimed no one even bothers to make a remake of the carb. You almost never see a Q-jet at any form of track whether it be drag racing, dirt track, road racing or anything else you can think up. I guess these people have not got the word on the advantage of Q-jet for extra power. Carter made a spread bore thermaquad came in 850cfm and 1000cfm yet you never see them either or a remake of them and they have the same bolt pattern as the Q-jet they used to advertise them as just bolt them on to your chevy. You look under the hoods of chrysler products today they like to mod there cars, holleys. Chevy never got the word what a good high performance carb the Q-jet is. All the low performance engines got the Q-jets all the high performance engines got holleys. This makes no sense if the q-jet were the better performance carb and back in those days gas was cheap just about nobody cared about what fuel milage there car got only performance. The Q-jet is stuck in time 1966 design to early eighties use no modifications. The holleys and there remake versions have constantly had improvements over the yrs made to them.

 

Sorry I have to disagree with you on this. A quad. set up right will out perform a holly anyday. Hollys are good because there simple. I have had quads. on my TA's that outperformed camaro's back in the day. Yes they are a B_t_h to set up/tune. But once it is, it stays that way and is VERY reliable. Remember we are talking about placing these carbs. on 30 and so on year old cars.

 

Some Quadrajet links for part I found while tuning mine should you decide to go that route. I went with Cliffs.

http://www.carburetion.com/quadrajet.asp
http://www.cliffshighperformance.com/parts.html
http://quadrajetparts.com/

 

Thanks for the sites!!!

 

The Carters became popular mostly because of price and availability and are leak free. The primary side is very similar to a qjet, but the secondaries are troublesome because they use a very inaccurate weighted system. That's really their biggest downfall. In oem form there were over 400 variations. The vast majority of hot rodders are not carb people. They spend all kinds of money on MSD ignitions, intakes, exhausts etc, but when it comes to a carb, they get the easiest, spend a few minutes turning the idle screws and unless it spits or falls flat on it;s face, they are good to go.

The qjet was designed to be a one casting fits all carb. Although there are many, many different oem calibrations, it is a "constant velocity" style carb, not a new concept at all. It was popular in that era, Makuni had it, SU from the 50s used the concept.
It's true that the secondary throttle plates are mechanically operated on a Qjet, but that literally means nothing, since the secondary fuel delivery is controlled by atmospheric pressure (vacuum) thru the secondary air valve and attached rods. Very similar to the vacuum diaphragm operated Holleys. Saved GM a lot of headaches and money.
The big difference is the improved low throttle metering and response for the daily driver grocery getter.
Ruggles will even tell you that his highly modified qjets will only meet the performance of similarly tuned Holleys. He has done all the testing.

In short almost any carb can be modded to run at the same performance and fuel economy levels, but the last on most carb people's list is the AFB.

 

Knowledge is power.

 

Below are my Dyno results. The blue line is pre-rebuild/re-jet and stock cam. Red is rebuilt and re-jetted per Cliff Ruggles suggestions with a xe268 cam.

It looks like around 2500 rpm he punches it and the accelerator pump shot takes it to around 12:1 but after that it stays around 13:1 all the way to 5k. I think this is good but what do you guys think of the A/f ratio?

 

You shouldn't have to go to 4 years of collage to tune a quad.
You put a Holley on a car adjust the float without wasting a gasket, set idle air mixture and idle, close hood and drive.
If your Holley leaks its you not the carb, Mine is dry as a bone and I never have to touch it and the performance is 10xs better than a bograjet, get over it!

 

Chevy had plenty Q-jets for use yet they never used them on there high performance engines sold to the public. They had plenty of dyno's to use to check things, all kinds of enginers at there finger tips. Obvoiusly none of this was telling them the Q-jet was the way to go for them. What hot rodders or racers wanted to do ment nothing to them.

Back in the early mid 60s GM in general had such wonderfull stuff as two speed automatics, little 327 engines put in 3800 lb impala's with around 3.08 rears. So it made sense to engineer a carb for the 1966 model yr that could do multiple jobs handling this mess with two very small front primaries to get this mess rolling off idle.

Hot rodders and racers for sure generally have tried more and know more then the street stroke and they could care less what kind of carb is on there car if it gave them an advantage. If Q-jets were the advantage for performance back in the day of carbs every racer mild to wild would have had one on there car there were billions and gillions of them around for access to them to use, plenty of parts back then easly available to modify them. Bottom line the truth it was never as good a performance carb. A nice street carb it also had some flaws.

The Q-jet is just like i said stuck in time what ever was good or bad about is still there.

The holley and its copies moved forward with all kinds of improvements both in quality of parts and extra tuneabilty from the holleys of the past. The best thing that ever happenerd to holley was competition. It forced them to constantly have to make improvements to the carb.

Never owned an AFB or edelbrocks version of it. I suspect edelbrock even when they first came out with the carb did not simply totaly copy everything about it. Most likely looked at the design and made some improvements to it.

But today when i look under the hood of street cars you see more edlbrock carbs on them then any other carb. But to listen to this forum they are junk use my whatever i like for carbs. In this new world of still word of mouth being ever more powerfull with the internet if they were the bad carb claimed edelbrock would have had to quit selling them no market for them. There are maybe seven other places to buy new carbs that would have quickly put him out of the carb business he would not sell them if he could not sell them. But atleast on the street looks to me clearly he is outselling all the other holley version carbs with the greatest of ease.

I had three pickups and four cars with Q-jets so i don't have anything against them.

 

I would like to see an A/F ratio graph for a Holley for comparison if anybody has one they can post from a dyno run. Let us know the model too.
Thanks