From a historical perspective, the Stingray's six-speed, paddle-shift automatic has been in development for at least three years. It's about as different from the '53 Corvette's Powerglide two-speed slushbox as the new 450hp LT1 is from the 150hp Blue Flame Six. In other words, they're not even in the same ballpark.
Comparing the Stingray's automatic with its more immediate predecessor from the C6 is more relevant. For that, we sought some input from two of GM's automatic transmission engineers, Rich Mardeusz and Gabe Gibson. Together they're sort of a tag team, with Mardeusz providing details on the hardware side, and Gibson covering the software algorithms, in particular as they relate to both the AFM (Active Fuel Management) and the various Driver Modes that can be selected with the turn of a knob. We'll start with the hard parts, and then move onto the intricacies of the software that controls them.
By way of background, Mardeusz has worked at General Motors since 1974, starting out in the Cadillac division on the chassis, electrical, and HVAC engineering groups. He then spent several years in the engine- engineering group, overseeing the controls hardware group for various powerplants. From there he moved to the transmission-engineering group, where he has spent the last 10 years. In addition to his current responsibility for the C6 and C7 Corvette automatics, he also oversees the six-speed, rear-wheel-drive automatic transmissions in the Cadillac ATS/CTS, Chevrolet Camaro, and Holden models.
Comparing the transmission layouts of the C6 and C7, Mardeusz notes that the Stingray's automatic has been moved forward in the chassis a few inches. That's been done for a couple of reasons: first, to make room in the rear to accommodate the new suspension structure (see our previous chassis/suspension installment for details); and second, to provide space for the transmission cooler, now located in the rear corner of the driver's side. (This placement has the added benefit of eliminating various piping and fluids.)
While the more-forward mounting provides better balance within the chassis, the new automatic is also 8.15 pounds lighter than the C6's unit. "We consider this a significant difference in weight," Mardeusz says with a note of pride. Trimming off excess poundage is a recurring theme on the new Stingray, as alluded to previously.
But how were GM engineers able to reduce the case size of the automatic, in order to allow this relocation? They went to a smaller torque converter—258mm, as opposed to the previous 300mm unit—which offers a 14 percent reduction in diameter and a seven percent shorter axial length.
According to Mardeusz, other numerical benefits of the smaller converter include a 31 percent reduction in both primary and secondary inertia. We won't delve into Newton's laws on this arcane aspect of physics (due to limits on both space and your author's intellect), but suffice it to say that this change alone resulted in a 0.1-second quicker 0-60 mph time.
Knowing Corvette owners' inordinate interest in enhancing performance, we raised a question about how much power the new automatic can handle. With an engineer's typical emphasis on precision, Mardeusz declined to provide a specific number, citing the need to do a damage analysis of the gearset, along with clutch capacity. Adding to the complexity, he says it would also require knowing the weight of the specific vehicle, along with the wheels and tires. But given GM's powerful computer modeling, used extensively during the three-year development of the transmission, that could be determined in just a couple weeks, if ever needed. Some of that work has actually already been done, as the data on torque and horsepower outputs of the new LT1 indicated that a major redesign of the C6 transmission was not needed, since the gearsets and clutch packs were already up to the task.
Even so, other upgrades were made, such as modifying the isolator clutch to improve the functionality of the Active Fuel Management feature. This unit now moves 2.5 times faster, Mardeusz says, providing a smoother transition to the engine's four-cylinder mode. In addition, a 258mm turbine in the torque converter provides additional driveline isolation to reduce vibration, needed in part due to the change in the length of the torque tube. Otherwise, most of the hardware is fairly similar, except for the size of the bellhousing, which is now slightly smaller since the innards take up less space.