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23 by Gary S. Vasilash > Editor-In-Chief INEERS by Gary S. Vasilash > Editor-In-Chief p Both of these transmissions are the GM 8L90 eight-speed. Clearly, the housings are different. That's because the one on the left is for the Chevy Corvette and the one on the right is for the Chevy Silverado 1500. Both applications require the ability to handle plenty of torque while providing high levels of efficiency. Corvette and (2) fit in the space that the six-speed had been located. According to Kaveh, a big enabler of this was a design that uses four gear sets and five clutches (two brake clutches and three rotating clutches). One similarity between the two transmissions is the location of the grounding clutches. They are rearward of the middle of the structure, out- side the gear sets. But for the new transmission, the grounding clutches are splined to the case. Consequently, the center support is eliminated and this means reduced weight. There are smaller steps between gears in the eight-speed compared to the six-speed, which helps maximize the horsepower and torque in both vehicles, which clearly have different uses for that horsepower and torque. In addition to which, it contributes to better fuel efficiency for both vehicles, which is of interest to drivers be they truck guys or 'Vette enthusiasts. For example, in the case of the more- aggressive first-gear ratio (4.56 vs. 4.03), it means that the Silverado is better from a start when towing a heavy load (the Silverado with the 6.2-liter and the eight-speed has a maximum available trailer rating of 12,000, while for the Corvette it means a faster time (the car with the eight-speed does a quarter mile in 11.9 seconds, which is 0.1 seconds better than the car with the six-speed). (Speaking of quick: according to Tadge Juechter, Corvette chief engineer, the eight-speed is as quick in shifting as a first-rate dual-clutch transmission. Why not develop a dual clutch for the application? One simple reason: the packaging situation. "There was no DCT off-the-shelf that would fit in our package and meet our coming performance in the Z06." That's as in 650 lb-ft of torque from the LT4 engine. Which we'll get to in a moment.) Here is a comparison of the gear ratios (:1) for the two transmissions: 8L90 6L80 eight-speed six speed First: 4.56 4.03 Second: 2.97 2.36 Third: 2.08 1.53 Fourth: 1.69 1.15 Fifth: 1.27 0.85 Sixth: 1.00 0.67 Seventh: 0.85 N/A Eighth: 0.65 N/A Reverse: 3.82 3.06 The 8L90 (along with the 6L90) is manufactured in the GM Toledo Transmission Plant in Ohio.