![]() The 10-speed first appeared in the 2017 Camaro ZL1 backing up the 650-horsepower, supercharged 6.2L engine. GM now also offers both 8- and 10-speed automatics. GM Automatic Transmission Gear Ratios Gears All this is handled with application of planetary ratios. It employs an even deeper First gear ratio of 4.02:1 with tighter gear splits but does not apply an overdrive for subsequent gears. The way the power is applied is different than the 4L80E / TH-400. This is a completely new and different transmission compared to the 4L80E. Our simulations reveal that this is worth anywhere from 0.10 to perhaps 0.15-second in a quarter-mile comparison between a stock 4L80E and a TCI Six-Speed. By reducing the rpm drop between gears, the engine remains within its power band. Then, because the six-speed is splitting ratios, the rpm drop between gears is less because TCI has turned this into a five-speed automatic with an overdrive. As an example, combining the TCI Six-speed’s 2.97:1 First gear with a 3.50:1 rear gear ratio is equal to a traditional TH-400 (or stock 4L80E) with a 4.19:1 rear gear. The overall First gear ratio is deeper at 2.97:1 which means the car builder can leave a taller rear gear ratio in the rear end and still have great First gear acceleration. The idea behind this conversion offers multiple overlapping advantages. Then, of course, Sixth gear is still 0.75:1 overdrive. The new Third gear in the TCI trans is 1.57:1, which is then overdriven to create Fourth gear which is 1.57 x 0.75 = 1.18:1 which is just 18 percent away from direct drive 1:1, which becomes Fifth gear. This creates the situation where the engine drops less rpm from First to Second gear. Then to create a new Second gear, the overdrive is engaged 2.97 x 0.75 = 2.23:1. Where the original 4L80E First gear is 2.48:1, TCI created a 2.97:1 First gear ratio. But in order to make this work properly, they began by making the overall First gear ratio deeper. Essentially what TCI did was to engage the overdrive at the back of the trans to split the gear spread between the original First and Second gear ratios and again between Second and Third. The TCI six-speed version has a few special additions to it. The 4L80E is a very large, heavy transmission but, like its original TH-400 cousin, it can absorb and transmit an enormous amount of engine torque. The overdrive ratio that’s added is 0.75:1. The original first three gear ratios are in fact still the same as the TH-400. The factory 4L80E-and the stronger 4L85-is essentially a traditional TH-400 three-speed automatic equipped with a fourth, overdrive gear. Jeff Smith: The TCI six-speed automatic is indeed a revamped or upgraded 4L80E. ![]() I’ve heard a little about this-did they add two more gears to the transmission? How is this different from the GM 6L80E transmission that is used in the Corvette or in the newer GM trucks? – R.F. I see where Summit Racing lists a TCI transmission that was originally a 4L80E – but they list it as a six-speed transmission. ![]()
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