2015 Corvette will get 29 mpg highway, GM says

DETROIT -- An 8-speed automatic transmission debuting in the 2015 Chevrolet Corvette boosts fuel economy by 3.5 percent over the six-speed it replaces and gives the General Motors long-running sports car an EPA highway rating of 29 mpg, its highest rating ever.

Tadge Juechter, the Corvette’s chief engineer, said a few more pounds of air pressure in the tires would have bumped the EPA rating to 30 mpg, but affected the car’s ride and handling. “We’ll be back next year and we’ll get to the 30,” he said Tuesday at a media event at GM’s proving grounds west of Detroit.

The 2015 Corvette Stingray with the 8-speed automatic will be EPA rated at 16 city/29 highway mpg and 20 mpg combined. The 2014 model, with a six-speed automatic transmission, carried an EPA rating of 16 mpg city, 28 mpg highway and 20 mpg combined.

The GM designed-and-built 8-speed automatic, the 8L90, is also scheduled for installation in the certain 2015 models of the Chevrolet Silverado and GMC Sierra pickups and will likely see duty in Tahoe and Yukon SUVs.

Because of the Corvette’s limited space, GM engineers had to keep the 8-speed the same size as the six-speed. They did that in part by moving the electronic controls off the transmission and by relocating the oil pump to the transmission’s sump. The new transmission, which is built in GM’s Toledo, Ohio plant, also uses lightweight components.

“GM’s new 8L90 eight-speed automatic represents a rare win-win-win scenario for customers,” said Kavoos Kaveh, global chief engineer for 8-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, he said.”

The Corvette is equipped with paddle shifters and fast-acting electronic solenoids that enable faster shifts than most dual-clutch transmissions used in sports cars such as the Porsche 911 Turbo. The 2015 Stingray with the 8-speed automatic is faster to 60 MPH than the manual transmission-equipped Corvette, Juechter said.

Long production life?

Though the transmission is just now starting production, it may not have a long production life. A new 10-speed automatic transmission, under development in a joint venture with Ford, is due out in about 18 months. It’s unclear if the 8-speed will remain in production once the 10-speed arrives.

For 2015, GM will install the 8-speed in the Corvette Stingray and Corvette Z06, as well as Silverado and Sierra trucks with 6.2-liter V-8 engines.

GM and Ford are working to boost the fuel economy of their pickups -- not only to meet tougher fuel economy standards, but to catch up with Chrysler’s Ram 1500 Ecodiesel, which carries a 28 mpg highway fuel economy rating. GM officials say they will release the Silverado 8-speed fuel economy figures later this fall as the truck gets closer to production.

Juechter said production of the 2015 Corvette began a few days ago at GM’s plant in Bowling Green, Ky. GM built just over 37,000 2014 Corvettes and still is working to clear a backlog of orders.