This thread might be considered borderline O.T. as the TQ was announced in 1969, but that is a lot older than some other carburetors regularly discussed. These are really great for those that want better performance on older V-8's but still retaining carburetors rather than going efi. The Carter thermoquad may be unique in carburetor design in that it is the only carb that was originally designed as a race only carb, and then because of its success, detuned for street/O.E. use. The Carter TQ, a spread-bore four-barrel, was announced in 1969 (and I realize this is later than the focus of many who frequent these forums). The first production were: 4846s - 850 CFM 4847s - 1000 CFM At the time, the carburetor companies were experimenting with press-in jets; and the first production run of both numbers featured press-in jets. It was thought that the press-in jets would be easier to change in the field (racecars need to tune for track, altitude, and temperature, among other criteria). This turned out to be a horrible mistake, as it was virtually impossible to reuse jets. Carter listened to the complaints, and the second production run featured conventional screw-in jets. To differentiate the two runs, the numbers were changed to: 4846sa - 850 CFM 4847sa -1000 CFM When Carter made an engineering change, but not sufficiently significant to change the base number, an "engineering change status" was appended to the "s". The first change would be the letter "a", the second, the letter "b'", etc. In 1971, Chrysler, which had been using the Carter AVS (smog carburetor) in order to meet federal smog emission standards, tried a detuned version of the TQ, an 800 CFM, on the 340 engine only. The horrible performing AVS was retained on most other Chrysler engines. In 1972, Chrysler switched to the TQ for virtually all V-8 engine. I have personally thought of the TQ as the "perfect Quadrajet"; as the TQ retained the good points of the Q-Jet, redesigned the bad points of the Q-Jet, and added the thermoplastic bodies. Carter had tests done by different independent testing facilities, that found the temperature of the fuel in the TQ bowl, on average, was 28 degrees F. lower than the temperature of fuel in the bowls of all metal carburetors. Since the rule of thumb is that a reduction of 10 degrees F. fuel temperature is a 1 percent increase in both power and fuel economy; it is easy to see the advantage of the TQ. Everything else equal, the TQ was 3 percent better than other carburetors. Can you feel 3 percent on the street? Probably not, but the racers could measure the difference; and a 3 percent increase in fuel economy on a production vehicle helped. Other TQ numbers of general interest (replacing an O.E. carburetor) would be: 9800s (800 CFM, electric choke, GM linkage) 9801s (800 CFM, electric choke, GM linkage) 9810s - this is a modified 9800s with the addition of an EGR port and a plug. 9811s - this is a modified 9801s with the addition of an EGR port and a plug. When considering the CFM of these carburetors (or ANY four barrel) once should look at the CFM of the primary and secondary individually. Thus: 800 CFM = 200 primary, variable 600 secondary 850 CFM = 250 primary, variable 600 secondary 1000 CFM = approximately 325 primary, variable 675 secondary. Among enthusiasts that have used them, there is a definite love/hate opinion of the TQ. WHY? Often, the DIY type loves to rebuild his own carburetor, often refusing to look at the directions. So he/she removes 8 screws holding the airhorn (top casting) to the bowl (center casting). Now to prevent damage to the thermoplastic bowl, he/she tries shaking the carburetor to remove the castings. Nothing happens. He/she now taps the airhorn (or the bowl) with a plastic hammer. Nothing happens except the irritation level to the DIYer. After a few hard taps, a flat-bladed screwdriver is attempted to be inserted between the airhorn and the bowl; and the bowl is cracked, making the bowl trash. Now he/she takes the carburetor to a professional who removes the two screws hidden behind the choke butterfly and sells the customer a new bowl. So what does the enthusiast tell his/her friends??? "The bowl warped, and had to be replaced"! The second issue causing the love/hate opinion is the bowl seals. Not used on the race versions, the first production street/O.E. carburetors used two O-rings in the bottom of the bowl. Initial laboratory testing turned up no issues; but use on the street resulted in fuel leaks (similar to the Rochester bowl plugs). Again, Carter listened (as did Rochester), and the second production street/O.E. carbs were equipped with what Carter called "Quad X-Rings"; the cross-section being in the shape of the letter "x" whereas the cross-section of an O-Ring is the letter "O". The X-rings solved the issue UNTIL the first carburetor rebuild. When we started manufacturing rebuilding kits in 1975, the cost of the O-Rings was $ 0.90/1000 pieces. That's right 90 cents per 1000. The cost of the X-Rings in manufacturer quantities were $2.00 EACH. What do you think came in the FLAPS carburetor rebuilding kits? So far as I am aware, the X-Rings came in the Carter kits, the Chrysler kits made by Carter for Chrysler, and a few (including ours) of the specialty rebuilding kits. I have never considered the ignorance (which can be corrected) of the enthusiast to be a carburetor problem. Today, even more than 50 years ago, the TQ is a wonderful addition to many of the 1950's, 1960's, and 1970's V-8 engines IF A SPREAD-BORE MANIFOLD IS AVAILABLE, NEVER THROUGH A SPREAD-BORE TO SQUARE-BORE ADAPTER. WHY so much better today? The plastic bowl REALLY helps minimize hot soak due to today's fuels. For migration to a different engine, the aforementioned numbers may be used, and Chrysler O.E. carburetors through the 1974 model year may be used. I do NOT recommend trying to use the 1975 and newer TQ's unless you are a professional with a well-stocked machine shop. WHY? The federal government was on the carburetor companies to make carburetors as difficult to modify as possible (RE: sealed idle needles in many 1978 and newer carburetors of all makes). The government knew that enthusiasts could change gasoline jets, so the modification on the 1975 and newer TQ's was to install large AIR jets. Thus to recalibrate for migration use, the enthusiast needs to carefully remove the pressed-in air jets, and fabricate smaller air jets to replace them (no Virginia, they are not available, or at least I am unaware of any). The 1975 and newer carbs are useful to the Chrysler restorer, and as a source of parts, other than the bowl assembly. Oone additional caviat. The 1000 CFM carburetors were produced with NO IDLE BOOSTER! Thus, while there are idle mixture screws, the signal to the idle circuit is very weak (remember - this is a race carburetor!). Idle adjustment on the street ranges from virtually impossible to completely impossible. Those that I know of that have successfully used these on the street has standard (manual) transmissions and generally could acquire an idle of 1400~1500 RPM. Part of the difference in CFM from the 850 to the 1000 was the removal of the idle booster. If there are questions, please post. Jon.
Great article Jon! Thanks for the information. Did any other OEM use the Thermoquad? Sent from my iPhone using The H.A.M.B. mobile app
Andy - yes. Lincoln on the 460 in (memory) 1974. We have sold a number of these to Ford enthusiasts for 390, etc, as this carb has the special kickdown arm required for use with a number of Ford automatic transmissions. Ford (export) used several different ones on performance models in Australia. Jon.
Thank you for some great info !! Thought about running one on my single carb tunnel ram 440, seems like the down side is it's a 75 or 76 model.
I also thank you. Very informative article; I had always thought that they were inferior to Rochester Quadrajets in every way way. You have opened my eyes.
Hi carbking, thx for the very interesting info - do you think a 9801s with the smallish 1 3/8" Primaries will also work well on a 1974 low comp 440? Same jetting as stock? Thomas
Would depend on the application. Should be fine, except for a possible very small hesitation when transitioning from primary to secondary, on a passenger application, or the "concrete cowboy" pickup application. I would not want to use it in a truck that was actually used as a truck. Jon.
Hey Jon, Excellent job,,,I always loved the old TQ,s,,,,,but then,,,, I am a Mopar man as well. It was an excellent carb,,,in the right tuners hands,,,,and an excellent heat insulated model as well. Thanks Tommy
Thank you Jon for the great write up! I'm an extreme TQ fan also! So many people hate them, I've gotten a few friends to use them and they say "Holy Crap", I never knew they could work so good. I'm not much of a carb tuner, I have a close younger friend that is very good at setting these up. My oldest brother ordered a 1972 Challenger with a 340. After riding in the new car with that Thermoquad, I was hooked! Also International used the for a few years on their trucks and Scouts. There is a Youtube video that shows one at full throttle. Type in 1975 Chrysler New Yorker 4bbl sound. It was kind of ironic when Holley designed most of their intake manifolds for the spreadbore design. A TQ on a Holley intake-no adapter needed. Thanks again!
Jon, I agree with everything you have said that the T.Q. is a great carb, however I have a question dealing with the deterioration of the glue used to hold the well bottom pieces to the main body. I have seen many of these come un glued. I am assuming that the alcohol in todays fuels has something to do with this problem. Is there an epoxy or bonding agent available that is capable of holding up to todays fuels? I have had problems finding a good dependable product. And no you guys, J.B.Weld does NOT work! Thanks in advance, Gary....
I have seen virtually no issues with this, but the cure is Permatex red threadlocker. Part number for the small tubes I buy is 27100. I don't think it is the alcohol, as Carter advertised these could be used with ethanol/methanol in race engines. More than likely, the glue is like all of us (we age and don't function as well as we once did!) Jon.
Hey, Jon...... Earlier this year I purchased a vehicle that came with an Edelbrock 1406. It came with a grocery list of big and little problems that needed to be sorted out. One of the issues was a build-up of pinkish crud in the fuel bowls and passages. The vehicle was from Arizona and I believe it had a history of short trips and long periods parked in between. Would a TQ carb have any noticeable advantage of less fuel evaporation and thus less residue in the carb? And add my thanks to the others for the fine article.
The thermoquad should have less fuel evaporation than any metal bowl carburetor; however, given enough time, the fuel will still evaporate. If replacing a "square bore" carburetor, change the manifold to a spread-bore. Spread-bore->square-bore adapters are for snake-oil salesmen. And I am not responsible for the speeding tickets you get when replacing the clone with the TQ Jon
I remember back in the 60's when my dad had a 59 Cadillac, it always had a pinkish powder residue on the top of the Carter AFB. I asked the old guy at our small town gas station what it was from. The ethel gas or the lead in it or the pink coloring of the gas. I'm not sure which. I always could tell when somebody was running ethel after that.
Interesting, thanks for posting. So did the performance and economy advantages of the plastic body ever make it to 2 bbl Carters?
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