The ThermoQuad was introduced in '71 for the 1st time as on oem carb with 800 cfm's. It had existed since '69 as an after-market performance carb avail in either 850 cfm's or 1,000 cfms and is know as the Competition Series.

The primaries on the '71-'73 340 T.Q.'s was approx 232 cfm's and a whopping 570 cfm's on the 2ndary side. The double booster design of the primaries gives the T.Q. an excellent port floor signal and exceptional fuel/air atomization. And the sophisticated metering system is very precise. And the carb was very 'change-able' to increasing EPA demands for cleaner running engines so it was easy to add smogger settings and parts that made the carb pass increasing emissions requirements.

The '71 340 T.Q. was a one year only design, derived from the 69 Competition Series carb. The carb is an air metered carb while all '72-up ThermoQuads are solid fuel metered.

CS series 850.......4846S for press in jets,
....................4846SA for screw in jets,
CS series 1,000.....4847S for press in jets,
....................4847SA for screw in jets,
'71 340 800.........4972 for 4 spd,
....................4973 for automatic,
'72 340 800.........6138 for 4 spd,
....................6139 for auto,
'73 340 800.........6318 for 4 spd,
....................6319 for auto.

These '72 carbs(oem)will suffer in performance if the correct casting # top is not used. The best 340 T.Q. is the '72 as it had the best metering system and it will make very close to the same power as the early '72-'73 big block 850 cfm carbs.

Over-all, these carbs are hard to beat in both gas mileage and performance!