Paddle-shift gearbox rivals dual-clutch performance, enhances efficiency
DETROIT – An eight-speed paddle-shift automatic transmission will be offered in the Chevrolet Corvette Stingray for 2015, enhancing the performance and efficiency of the 2014 North American Car of the Year. Designed and built by GM, the new transmission delivers world-class shift times that rival the best dual-clutch designs.
The all-new, GM-designed 8L90 eight-speed is expected to contribute up to 5-percent greater efficiency, when compared to the previous six-speed automatic. EPA fuel economy test results are pending and will be announced later. It also makes the Corvette Stingray one of the few sports cars to offer the choice of a conventional manual transmission or an eight-speed automatic.
“Corvette Stingray’s new eight-speed automatic delivers the comfort and drivability of a true automatic transmission, as well as lightning-fast shifts and the manual control that enhance the performance-driving experience,” said Bill Goodrich, assistant chief engineer for eight-speed automatic transmissions. “It was designed to enhance the Stingray’s driving experience, with performance on par with dual-clutch designs, but without sacrificing refinement.”
The available 8L90 transmission is based on the same eight-speed automatic that will be offered on the supercharged 2015 Corvette Z06, but with unique clutch and torque converter specifications matched to the torque capacity of the Stingray’s LT1 6.2L naturally aspirated engine.
For performance driving, the transmission offers full manual control via steering wheel paddles. A new transmission-control system and unique algorithms deliver shift performance that rivals the dual-clutch/semi-automatic transmissions found in many supercars – but with the smoothness and refinement that comes with a conventional automatic fitted with a torque converter.
The transmission controller analyzes and executes commands 160 times per second. Wide-open throttle upshifts are executed up to eight-hundredths of a second quicker than those of the dual-clutch transmission offered in the Porsche 911.
Smaller steps between gears, compared to the previous six-speed automatic, keep the engine within the sweet spot of the rpm band, making the most of its horsepower and torque to optimize performance and efficiency.
With four gearsets and five clutches, creative packaging enables the new eight-speed automatic to fit the same space as the previous six-speed automatic. Extensive use of aluminum and magnesium make it more than eight pounds, or 4 kg, lighter than the six-speed. Design features that reduce friction contribute to the expected 5-percent greater efficiency.
The 8L90 is built at GM’s Toledo, Ohio, transmission facility.