Throughout the 1970s and early 80s, the Carter Thermoquad (TQ) was a popular carburetor found on many Chrysler products as standard equipment, and on some Ford Motor Company vehicles, as well. The earliest version was in the Competition Series first released in 1969. Production versions followed in 1971 on Chrysler’s 340 c.i. engine. The TQ was discontinued briefly in the mid 70s, then reintroduced as the 9000 series for its final production years.
The Thermoquad was a large four barrel configuraton, with what was called the spreadbore design, two smaller primaries for fuel economy and two large secondaries. When those secondaries kicked in, you knew it. It came standard on many Chrysler engines including the big 440 c.i. mill, most 360s and even on many 318s. International Harvester used the TQ sporadically on its 345 and 392 engines. The big Lincoln 460 c.i. engine occasionally sported the TQ.
A quite distinctive touch on this carburetor was the material of which the main body was constructed. Between the lower throttle flange below and the aluminum bowl cover above, this black phenolic plastic section was designed to provide a cooler operating environment for the gasoline in the float bowl. It worked to effectively lower the operating temperature by about 20 degrees. And this plastic resin main body, then, is what gave the thermoquad its name.
The TQ was a dual bowl carburetor with the bowls housed in the phenolic plastic body. Each bowl served half of the carburetor: one primary and its related secondary. The first thermoquads employed brass floats while the later versions after 1973 were all nitrophyl floats.
The spreadbore design feature was shared in common with other carburetors, even those from other manufacturers, including popular Rochester and Holley designs that shared a common flange connection with the Thermoquad. Therefore many of these carburetors can be swapped out with the right adapter.
The original factory Competition Series of the TQ came in two flow ratings, 850 and 1,000 cfm. Production versions ranged from 750 to 850 cfm. This carburetor was also produced in aftermarket versions rated up to 1000 cfm.
Produced over such a long lifespan, the TQ came in literally dozens of versions, and many parts are not interchangeable from one version to the next. Correct identification of which version your engine carries is therefore critical. There are many different numbers found on the carburetor, but most of them are casting numbers. The actual model number is stamped into the lower left bolt flange at the rear of the carburetor. Some early versions also had a tag displaying the model number attached to one of the mounting bolts. Some later versions also included a bar code sticker identifying the version. Some rebuild kits and all nitrophyl floats remain available.