I mentioned the TQ in another thread about carburetors, questions were asked, and not wanting to totally hijack the original thread, started this one.
The Carter TQ is a spread-bore design, and can generally be used as a replacement on a Chevy spread-bore intake, replacing a Rochester Q-Jet (quadrajet).
The TQ is a carburetor those building a performance V-8 should at least consider.
The initial release of the TQ was 5 February 1969. Two models were released: (1) 4847s (1000 CFM) and (2) the somewhat smaller 4846s (850 CFM).
The drag racers and weekend warriors loved the carburetor with one exception. Holley used O-rings for sealing on some of their fuel valves succesfully, so Carter tried using O-rings for sealing main metering jets and promoted the press-in jets for easy removal and installation. The jets were easy to remove, and NEW jets easy to install. What Carter didn't consider is that when racers dial in a carburetor, they may change jets several times. Once the press-in jet was installed, then removed, it was quite difficult (but still possible) to reinstall.
A clamor arose for conventional screw-in jets. Carter listened, and very shortly into the production run, new threaded castings, and new screw-in jets were introduced. The carburetor numbers were the same, but with an added "engineering change status". The 4846s became 4846sa, and the 4847s became 4847sa.
The 4846s and 4847s were the only TQ's to use the press-in jets; Carter had learned its lesson.
1969 was close to the beginning of smog emissions (1966 California, 1968 Federal), and Chrysler was using the smog developed AVS Carters on most V-8 applications in order to pass smog emissions. Since the thermoquads were more efficient than metal carburetors, Chrysler asked Carter to reduce the size of the TQ and de-tune it for the street. In 1971, Chrysler used the TQ on performance 340 CID engines only; wanted to test the TQ before committing entirely to its use. The 1971 340's were very successful, and in 1972 Chrysler discontinued the AVS on the 400 CID, and switched to the TQ. In 1973, Chrysler switched to the TQ on the 440 as well, so passenger 4-barrels were now TQ. Holley square-bore 4-barrels were continued on some truck applications.
TQ problems:
The worst issue with the TQ was the afore-mentioned press-in jets, but two additional issues arose.
(1) The initial "street" TQ's used an O-ring as a seal in the secondary well. Those familiar with Q-Jets can think of the Q-Jet well plugs. While these worked well in initial testing, they were found to leak in service on the street. Carter designed what they called a "quad X-ring". To understand, an O-ring is a ring from a material with the cross-section of the letter "O". And the "X-ring" is a ring of a material with the cross-section of the letter "X". Carter changed the part in new carburetors, and issued a recall for existing carbs to be modified at the dealers. This should have ended the issue, BUT: Carter revised the bill-of-material for factory rebuilding kits, and Chrysler obtained kits from Carter so the genuine Carter kits and the Chrysler kits had the X-rings. But everyone knows
that dealer prices are too high so there is an aftermarket. When we started the manufacture of carburetor rebuilding kits for the thermoquad in about 1977, prices for manufacturer quantities of 1000 pieces of O-rings were 90 cents, and for X-rings $2000 !!! That is not a misprint. O-rings were less than 1/10 of a cent each, and X-rings $2.00 each in quantity. Guess what came in the aftermarket kits???
(2) The second issue was the "cracked plastic bowl" often with a few expletives added. Q-Jet rebuilders can identify with the cause of this problem. The home enthusiast wants to rebuild his TQ, so he acquires a kit, places in instructions under the parakeet cage, grabs his screw-driver and removes the 8 screws holding the TQ together. It doesn't come apart. Not wishing to damage the plastic, he shakes it, the taps it with the plastic handle of a screw-driver, finally with a plastic hammer. Nothing works, it still doesn't come apart. Now frustrated, he inserts a screw-driver between the bowl and the air horn and attempts to pry it apart, resulting in breaking the bowl. Now more than frustrated, he takes the carb to a mechanic, who opens the choke butterfly exposing the two additional screws that were shown on the diagram now somewhat messy from the parakeet
So when asked about his TQ, does he tell his buddies about his experience? No, he tells them he had to replace a cracked bowl!
Should someone wish to use one of the TQ's on a Chevrolet V-8, there are 4 numbers to watch for:
(1) 4846s or sa (850 CFM manual choke) high performance/race
(2) 4847s or sa (1000 CFM manual choke) high performance/race
(3) 9800s (800 CFM electric choke) street performance
(4) 9810s (9800s modified with a pluggable EGR port)
From a Chevrolet standpoint, other numbers are merely parts sources.
Advantages versus a Q-Jet
(1) largest available spread-bore CFM
(2) Efficiency
(3) Weight - approximately 2 pounds less than a Q-Jet. This may sound trivial to some, but I spent thousands removing weight from my own playtoy, and it still basically appears stock
(4) Documentation - as the TQ was originally sold as aftermarket, Carter produced a LOT of tuning information, Rochester never did
(5) Parts availability - like (4) above, as the TQ was sold as aftermarket, a wide selection of tuning parts were available
Disadvantages:
(1) Parts availability (today) is somewhat worse than the Q-Jet, but is rumored there is a grumpy old hillbilly in Missouri that makes a lot of parts
(2) Knowledgeable mechanics - not too many TQ specialists left today
Jon
