Really an evolution of the long line of Carter four-barrels, the TQ was a break in tradition, moving from the square-bore configuration of the earlier AFB and AVS carbs to a spread bore layout similar to the Rochester Quadrajet. The original OEM ThermoQuad, debuting on the , was a unique unit with different castings, metering circuits, and tuning parts. These carbs are quite rare, and pretty much orphans today outside the world of authentic restorations. Subsequent carbs were produced in huge numbers, and saw only minor changes through rest of the production run.
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The Carter TQ, a spread-bore four-barrel, was announced in and I realize this is later than the focus of many who frequent these forums.
The first production were: s - CFM s - 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: sa - CFM sa 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". In , 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 CFM, on the engine only. The horrible performing AVS was retained on most other Chrysler engines. In , 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.
Since the rule of thumb is that a reduction of 10 degrees F. 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.
Often, the DIY type loves to rebuild his own carburetor, often refusing to look at the directions. Nothing happens. 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.
Initial laboratory testing turned up no issues; but use on the street resulted in fuel leaks similar to the Rochester bowl plugs. 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. WHY so much better today? For migration to a different engine, the aforementioned numbers may be used, and Chrysler O. The federal government was on the carburetor companies to make carburetors as difficult to modify as possible RE: sealed idle needles in many and newer carburetors of all makes.
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 and newer carbs are useful to the Chrysler restorer, and as a source of parts, other than the bowl assembly. Oone additional caviat. 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. Part of the difference in CFM from the to the was the removal of the idle booster. If there are questions, please post.
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