2015 Corvette Stingray: Inside GM's new 8-speed gearbox
The rapid proliferation of 8-speed automatic transmissions throughout the automotive industry is no coincidence. Transmission giant, ZF, designed a cutting-edge 8-speed gearbox capable of adapting to anything from pickups to exotics and everywhere in between. With a heavyweight clientele consisting of such automakers as Chrysler, Jaguar/Land Rover, BMW, Mercedes-Benz, and Acura, to name a few, it seemed only a matter of time before GM jumped on the ZF bandwagon - but they didn't.
Because transmissions in tightly packaged models such as the Corvette Stingray must adhere to specific form factors, GM decided it would be more cost effective to simply build an 8-speed automatic in-house than to modify a ZF unit. Following years of research and development, GM's latest autobox entered production bearing some extraordinary specs: 8 pounds lighter than the outgoing 6-speed, able to withstand over 650 lb-ft of torque, up to 5-percent improvement in fuel efficiency, and shift times on par with dual-clutch gearboxes. Given these data points, it should come as little surprise that GM's 8-speed automatic transmission is set to make its formal debut in the 2015 Chevy Corvette Stingray. But, not unlike ZF's versatile package, GM's transmission was designed to handle a wide variety of applications. Although the automaker has yet to confirm which cars and SUVs are slated to receive the new transmission, we do know it will be offered on all 2015 Chevy Silverados and 2015 GMC Sierras equipped with the optional 6.2-liter V8.
Diminishing the stigma of automatic Corvettes
Until Americans acknowledged the superior performance benefits of Porsche's now-revered PDK dual-clutch automatic transmission, driving a two-pedal Porsche was seen as something of a sacrilege. This enthusiast-driven illusion holds true with the Corvette, but will likewise vanish soon after the performance advantages of its new automatic are recognized. Fact: the 2015 Corvette Stingray 8-speed is both faster in a straight line and around a racetrack. These predicable-yet-impactful truths are certain to be further exemplified in the forthcoming 2015 Chevrolet Corvette Z06, which will be the first of its kind to offer an automatic transmission.
Circuit to city
For all its speedy gear changes around the racetrack, we found ourselves more impressed with the manner in which the new 8-speed automatic conducted itself around town. Whereas dual-clutch automatics tend to tremble when accelerating from a stop (caused by clutch slippage), the Corvette's more-conventional torque converter employs a new turbine damper to provide smooth, linear power delivery from a standstill while directing more power to the wheels than before. Shifts during normal driving went virtually unnoticed. Rather than hunting for gears during sudden hard acceleration like Lexus' 8-speed - GM's transmission software knew exactly which gear to select for the situation. The only gripe we had with the new automatic involved paddle shift response times. While GM claims its 8-speed can shift .08 seconds quicker than Porsche's PDK, there is still a noticeable delay between the time you depress the paddle shifter and the physical gear change. This, of course, is not an issue with PDK. Nevertheless, it's safe to say GM's efforts to develop a cutting-edge, multi-use transmission paid off. We just hope it finds its way into popular GM models sooner rather than later.
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