Enhanced TR6060 Transmission
Another factor in the performance and durability of the ZR1 drivetrain is of course the transmission, which is an evolved version of the T56 we know and love. "The TR6060 launched with the 2008 model year, and that was just one more step in taking a transmission that 10 years ago was capable of 350 lb-ft and getting it up into the torque ranges of today," says Kline. Features like increased gear widths and a new synchronizer package all carry over into the 2009 ZR1, but the new car also gets high-strength materials, like an SAE 9310 input shaft and SAE 4615 mainshaft.
Additionally, fifth and sixth gear now sport higher-strength SAE 8822 material. Surely one of the reasons for this is that they'll be used to their full ability. Thanks to its application-specific close-ratio gearset, the ZR1 will make better use of its overdrive ratios and will actually top out in top gear--a first for six-speed Corvettes. Rpm drop during gear changes will be minimized--and first gear (by carrying a taller 2.29 ratio) also allows better traction at low speed, including during a launch. Other slight changes, like alterations to the gear helix angles were made for the ZR1, but despite all of its strength-enhancing features, GM says there's no driver-perceptible difference between this car's tranny and the other TR6060s in the lineup. "It's a very nice performance package, with the same type of no-noise operation that you expect out of the Tremec products--but with the strength to handle the torque of the LS9," says Kline.
Beefed-up Getrag 626 Axle Assembly
During development, the ZR1's rear axle assembly underwent a whole host of improvements over the Z06 unit--and with the exception of a new Dexron LS gear oil (which features better performance at high temperatures), none of them trickle down to other Corvettes. This is primarily due to expense concerns, but it's also because GM considers the axle assemblies in the base and Z06 cars adequately strong for their applications. (We'll bet that some hard-charging enthusiasts with modded Vettes might disagree with this latter assertion!)
Most significant is the Getrag 626's main housing, which is now made from a high-grade 357-T6 sand-cast aluminum. Ditto for the right side diff cover. The left side cover, forged on the Z06, is now machined from SAE 4140 steel billet, and it's "a very pretty piece," according to Kline. The ring-and-pinion is still a 3.42 ratio, but it's made from tougher material and is single shot peened. The differential output shafts are now high-grade 4340 steel. Other material changes, including to the differential itself, exist throughout the axle assembly. The great news is that Kline says many of these items should swap into non-ZR1 Getrags without much trouble.
Specially Engineered Axles
The axle halfshafts themselves were not developed by GM Powertrain, but rather by Corvette platform engineers. Aside from being high-strength, Jim Danahy told us that a 33mm halfshaft is used on the passenger side of the car, while a 40mm unit is used on the driver side. Why the drastically different diameters? "It helps to decouple the resonant frequencies of the individual sides of the suspension," he says. In other words, it's to combat wheelhop. It's a nifty solution that we'd like to see more widely implemented on other GM performance cars.
The TR6060 transmission gets several upgrades to ready it for ZR1 duty, but they are all internal: the casing was already beefed-up for all 2008 Corvettes in anticipation of handling the torque of the upcoming LS9. This is good news for enthusiasts, as base and Z06 owners should be able to swap in ZR1 internals if the need arises on high-horsepower race applications. | 
The only options for the entire car (other than chrome rims) can be found in the cabin, where a "luxury package" gives you items like power-adjustable seating with special trim, a leather-wrapped interior with four color options, a navigation system, and Bluetooth capability, along with a reduction in the car's power-to-weight ratio (according to Jim Danahy, ditching this package will allow the car to come in a good bit below the projected curb weight we've quoted). All ZR1s get special headrest embroidery and logo-emblazoned sill plates. | |