DETROIT — The all-new, GM-developed Hydra-Matic 8L90 paddle-shift eight-speed automatic transmission offered in the 2015 Corvette Stingray and Z06 enhances performance and efficiency, while delivering exceptional refinement and world-class shift responsiveness that rivals the world’s best dual-clutch transmissions.
In fact, in the 2015 Corvette Stingray, it enables a class-leading 29-mpg EPA highway estimate – a 3.5-percent increase in fuel economy over the previous six-speed automatic — and a quicker 0-60 time of 3.7 seconds, all while delivering wide-open-throttle upshifts quicker than those of the dual-clutch transmission offered in the Porsche 911.
“GM’s new 8L90 eight-speed automatic represents a rare win-win-win scenario for customers,” said Kavoos Kaveh, global chief engineer for eight-speed automatic transmissions. “It offers greater performance and efficiency, while weighing less than the transmission it replaces. That’s a rare accomplishment in the industry today — and one for which GM has been awarded more than two dozen patents.”
With four simple gearsets for optimal efficiency and five clutches (two brake clutches and three rotating clutches), creative packaging enables the new eight-speed automatic to fit the same space as the previous six-speed automatic — and the powerflow only uses two open clutches for low spin losses, which enhances efficiency. Extensive use of aluminum and magnesium also make it more than eight pounds (4 kg) lighter than the six-speed.
The greater overall performance and efficiency enabled by the 8L90 in the Corvette is due primarily to a new, wider 7.0 overall gear ratio spread, which enhances off-the-line performance with a more aggressive first gear ratio – 4.56 vs. 4.03 on the six-speed – helping achieve the quicker 0-60 time.
The top gear ratio is 0.65 vs. the six-speed’s 0.67. Combined with a new, numerically lower 2.41 rear axle ratio in the Stingray vs. the 2.56 gear used with previous six-speed automatic models, engine rpm is reduced by 8 percent (123 rpm) on the highway at 70 mph. The lower engine speed reduces fuel consumption, while a new torque converter design enhances refinement, particularly during low-speed gear changes.
Stingray models equipped with the Z51 Performance Package feature a more aggressive 2.73 axle ratio, while the Corvette Z06 features the 2.41 axle ratio.