All the horsepower in the world is useless until it's transferred to the wheels. Which makes the transmission an unsung hero of the new '14 Stingray, since the only obvious manifestations of its pivotal performance role are either a shifter or a pair of paddles on the steering wheel. Otherwise it's just a mysterious box concealed in the chassis.
All the more reason to dig into the remarkable details of the C7's "trans actions," in eager anticipation of the next installment in our Stingray series. That's when our editors plan to man the wheel and stomp on the loud pedal. We can hardly wait, but for now we'll continue to whet your appetite for what is shaping up to be the best Corvette ever.
To that end, let's take a closer look at the Stingray's new transmission offerings. Looking at Corvette-buyer preferences overall, historically the breakdown has been 70 percent auto, 30 percent manual (on models offering a choice between the two). We'll start with latest developments on the latter.
First off, the seven-speed manual does not merely consist of an extra OD gear grafted onto the existing C6 setup. For a look inside the case and all the upgrades, we spoke with GM's Todd Rooney, Global Assistant Chief Engineer for RWD Manual Transmissions. His background at GM dates back more than a dozen years, through three eras of Corvette trannies, as he's worked on the C5's T56, the C6's TR6060, and now the C7's TR6070. His responsibilities have also included overseeing clutches, clutch-release hydraulics, and manual shifters for RWD drive applications, on both U.S. and international GM models. Additionally, he's worked on automatic transmissions and AWD/4WD systems, as well as other driveline components.
Rooney's first assignment was as development engineer on the C5 manual transmission clutch, so he has an in-depth historical perspective on all the proverbial "gear changes" over the years. Since that initial work, he has been involved in a number of other Corvette-related projects, both in production and prototype arenas. Out of all his varied assignments, he notes that, "I feel that being a part of the Corvette legacy at GM is truly an honor."
Starting with the basic overall unit, Rooney notes that the gears from First to Sixth on the C7's manual are fairly similar to the C6's, except for the aforementioned additional OD, which required extending the case 42 mm to make room for the extra gearset. This change upped the overall weight slightly, by about 3.3 pounds, a gain that was partially offset by the shortened torque tube required.
All of the upgrades for the new transmission (including Active Rev Match, twin-disc clutch, dual-mass flywheel, and Seventh gear, which we'll cover below) are included in both the base and Z51 models. The Z51 option, however, has different ratios since it's intended for track duty, as noted here:
Clearly, the Z51's lower (numerically higher) close ratios in the First through Third gears will make for quicker acceleration, while the higher ones should provide fuel efficiency similar to the base model's—assuming drivers are able to keep a light touch on the throttle. From there, things get more involved, with an all-new output shaft, counter shaft, and internal shift system (forks and rails). The most obvious difference is evident in the relocation of Reverse from the upper left to the lower right, since the new Seventh gear fills in where Reverse is found on the C6 shift pattern.
The change in the shifter layout only hints at the extent of the upgrades. We're told the feel of the clutch is improved, thanks to the incorporation of a new twin-disc unit from LuK. Each of these discs measures 240 mm, compared with 290 mm (total) for the previous single-disc setup. The twin configuration lowers inertia, so there's less effort required, with a cleaner, smoother action, Rooney points out. Pedal effort is a touch lighter, too.
Sounds simple enough, but Rooney admits to sweating the details on the dual-mass flywheel, also supplied by LuK. Designing it presented a quandary, in that a heavier one reduces noise and vibration, but its extra rotational mass inevitably degrades acceleration. Conversely, one with less mass makes for better performance but feels harsher. Balancing these two competing concerns required some fresh thinking and a lot of late nights on the CAD system.
"The C7 market demands a step up in refinement," Rooney notes. "But we didn't want to sacrifice any performance either." So what they came up with is an arrangement called Dual Flywheel Lite. Sounding a bit like the name for a "great tasting, less filling" beer, this relatively new setup has reduced mass at the outer edge. Yet it's still up to handling ZR1 power levels, and likely more, a trait that will be increasingly important as Stingray owners begin enhancing the output of the car's LT1 engine. To minimize noise and vibration, the engine's firing pulses, which are normally transmitted to the driveshaft, have been isolated somewhat with springs, among other measures.
Also contributing to the driveline smoothness is a new Active Rev Matching system. Basically what it does is make the Corvette both easier and more exhilarating to drive by blipping the throttle to match engine speed with each anticipated gear change, resulting in smoother shifts. Although the concept is not completely new (the Nissan 370Z offers a similar feature), the methodology is different on the Stingray, Rooney says.
Breaking it down, this setup stars with a GAP (Gear Absolute Position) sensor. It basically consists of two components, a 3D Hall Effect transducer on the transmission and a magnet on the main shift rail. As the magnet moves, either in rotation and/or back and forth, the 3D Hall Effect transducer identifies its spatial location (hence the 3D reference). That information is relayed to the engine controller, and an algorithm and other computer programming adjust engine speed so it's in sync with the transmission. In other words, its taps the throttle for you.
But don't think it turns the Stingray into a numb, driverless automaton. It's really just a helping hand for entry- to intermediate-level drivers. Feel free to insert names of our editorial staff here. More-seasoned track stars can turn off Active Rev Matching and heel-and-toe shift to their hearts' content. We'll report back on how well we managed this tap dance in our next installment.