The race to higher gear counts is in full swing, and automatic gearboxes are leading the way. Driven partly by marketing one-upmanship and partly by the need to meet ever-tougher fuel-economy mandates, eight-speed autoboxes are everywhere, Chrysler’s running a nine-cogger in select models, and 10-speeds—from Ford, GM, Volkswagen, and others—are just around the corner. The General’s own in-house-developed eight-speed units (for its trucks and rear-drive V-8 cars) are just making an appearance after work on them had all but stopped during the company’s plunge into bankruptcy in 2009.
Now the Corvette gets updated with its rear-axle-mounted version of this new eight-speed automatic. Why is this news? While we’re firm believers that manual transmissions still provide a higher and more nuanced level of organic driver involvement and control, it’s no secret that high-performance cars are often faster and quicker during limit testing when equipped with the automatic gearboxes. Ferrari and Lamborghini have gone exclusively to automatics, and the new Porsche 911 GT3 and the 911 Turbo are automatic-only. One might say that Chevrolet is taking a page from the Porsche playbook by even offering an automatic in the forthcoming Z06—a model that had been limited to manual-transmission offerings in the past. Its supercharged LT4 small-block V-8, with 650 horsepower and 650-lb-ft of torque, will be the most powerful engine General Motors has ever produced. So don’t think of an automatic, even if it is a more common planetary-gear type rather than the more exotic dual-clutch variety, as a handicap the Z06 must suffer.
Gears With Benefits
How can we be so sure? Chevy hasn’t shown us a running Z06 in the flesh, but the company did let us sample the new eight-speed automatic in the 2015 Stingray and Chevy claims that the new ’box is quicker in a straight line than the manual. We discovered that the old six-speed auto was quicker than the manual version with individual tests of Stingray convertibles, but knocking another tenth off of the zero-to-60-mph and quarter-mile times puts the estimated times of the eight-cog Vette perilously close to those recorded for the C6 ZR1 in the first metric and nearly into the 11-second range in the second.
The new GM 8L90 eight-speed automatic, which will also go to work in the 2015 full-size trucks and SUVs equipped with the 6.2-liter V-8, doesn’t hamper the fun one bit. On a road course, taking hot laps in an automatic that performs ignition-spark-cutting upshifts and positive-torque downshifts (engineer jargon for blipping the throttle to match revs) quicker than humanly possible allows the driver to concentrate on the steering and braking, potentially turning quicker laps in the process. Plus, from our seat-of-the-pants perspective, the GM 8L90 shifts as quickly as any dual-clutch unit available. Corvette engineers benchmarked the ZF’s dual-clutch automatic that goes into the Porsche 911 and claim the new GM ’box actually shifts quicker in some cases.
Goin’ With the Flow
Several laps of GM’s Milford Road Course revealed that the transmission programing in good-old “D” with the car’s Performance Traction Management switched on is pretty good for track duty. It’ll hold gears up to redline, downshift by itself just as one might do while tapping the steering-wheel paddles, and automatically upshift when it should. A two-three midcorner upshift doesn’t upset the chassis as it might with a manual transmission because the torque flow at gearchanges is smoother. We’re not saying the automatic is more fun to drive than the seven-speed manual, but don’t be surprised if the next Corvette we put on a racetrack has an automatic.
GM wouldn’t confirm whether the automatic Corvette is quicker on the track, but the Z51-equipped cars are certainly built for it; they will lap continuously for a full tank of fuel without overheating. When the 8L90 goes into the Z06, it’ll have two transmission coolers—one in the hindquarters, as with regular Stingrays, and another farther up the chassis laying flat on the underbelly.
Through ample use of aluminum and even some magnesium (a first for GM automatics), the new 8L90 weighs eight pounds less than the six-speed 6L80 it replaces, so curb weights should not increase for 2015. The new transmission gets its eight ratios, with a 7.02:1 spread, from four simple planetary gearsets and five clutches, three of which are always closed for increased efficiency. And speaking of efficiency, Chevy says it missed its goal of achieving a 30-mpg EPA highway rating by the narrowest of margins—one hundredth of a mpg. Corvette chief engineer Tadge Juechter says GM will retest the car next year with an extra 2 psi in the tires in an attempt to attain the 30-mpg label. That’ll require Chevy to change the recommended pressure on the door-frame placard and then print in the owner’s manual that it is okay to run at a lower pressure for “comfort.” That’s a trick Porsche’s been doing for years.
Watch this space for a full test of the eight-speed-automatic 2015 Stingray as soon as we can hook up our gear to one. All that talk about another mile per gallon is nice, but we’ll let you know if our prediction of a 0.1-second quicker zero-to-60 time compared with that of our last test of a six-speed automatic Vette—down to 3.6 seconds—pans out.
Mais bon pour en avoir conduit des centaines... la 8 vitesses reste plus confortable. Ça n’enlève rien a la DSG qui effectivement est une référence dans le monde de l'automobile.
