Corvette Stingray Debuts GM’s New 8-Speed Transmission

General Motors Co. is introducing its new 8-speed automatic transmission on the 6.2-liter V-8-powered 2015 Corvette Stingray that is hitting showrooms now.

The new 8L90 gearbox will spread to GM's half-ton pickup trucks and SUVs that use the same driveline. The unit was designed by the company and is being produced at GM's transmission plant in Toledo, Ohio.

The 8-speed tranny is 5% more fuel efficient than the 6-speed automatic in the current Corvette. The system also is 8 lbs lighter and occupies the same volume as the 6-speed it replaces.

GM claims the 8L90 shifts at least as fast as a comparable dual-clutch system. The new gearbox's processor speed is four times that of the company's Gen 1 transmission.

The new gearbox is a major factor in delivering a U.S. highway fuel economy rating of 29 mpg for the Stingray's upcoming supercharged 650-hp variant of the 6.2-liter powerplant.

GM says it considered but rejected the twin-clutch automatic architecture favored by Porsche AG. The company opted for eight gears because of the need to share the new gearbox across a broad range of vehicles. A more compact package size was another major attraction. The design's smaller planetary gear set neutralizes the great weight of other components compared with a twin-clutch system, according to GM.

Fitting the 8-speed into the Corvette's compact engine compartment was made more difficult by the need to meet new European pedestrian protection regulations. The rules all but require more space between the hood and driveline components below. The GM system uses four planetary gear sets with two open clutches. An off-axis binary pump with two output levels helps minimize package size.

The 8L90 gearbox cuts weight mainly by material substitutes that include a magnesium piston house and channel plate and aluminum input carrier, rotating clutch housings, clutch pistons and bell housing. The input carrier shell is made from high-strength low-alloy steel.