The LT4 cylinder-head design is essentially the same as the LT1’s, but the LT4 units are more robust. They are rotocast from A356T6 aluminum alloy, which yields castings that are stronger and better able to withstand high heat. Heat management is also aided by a larger-capacity oil cooler for the otherwise standard Z51 dry-sump oiling system.
Unlike the LS9, the LT4 does not have titanium connecting rods. Says Rydzewski, “We went with a high-strength powdered-metal connecting rod with a lot of machining to take the mass out where we didn’t need it and that way we kept the rotating mass down while at the same time maintaining the safety factors on this engine up where we want them to be.” This decision offers insight into how Chevy keeps adding performance to the Corvette from one generation to the next without commensurately increasing the price of the vehicle.
Though Chevy has not completed fuel-economy testing and certification, and therefore isn’t sharing numbers or saying whether or not this new Z06 will avoid a gas-guzzler tax—which the naturally aspirated C5 and C6 Z06s were able to do, but not the supercharged ZR1—low fuel consumption was a high priority from the start. Getting to that goal with the LT4 will be helped in large measure by the fact it retains advanced technologies already found on the LT1, including direct injection, continuously variable valve timing and cylinder deactivation.
Transmission: Eight is the new Six
Every previous version of the Z06, going all the way back to 1963, has only been available with a manual gearbox. Owing to advancing technologies and changing consumer tastes, the Corvette team decided to offer the C7 Z06 with an automatic transmission, as well. But the existing 6-speed automatic used in the C6 would not suffice, so Juechter challenged engineer Bill Goodrich and his colleagues in the transmission-engineering group at GM Powertrain to design a new one.
In essence, the same engineering goals that guided LT4 engine development also drove the creation of the new 8-speed automatic. Compared with the 6-speed automatic it was to replace, the new unit had to be lighter, strong enough to withstand the supercharged engine’s enormous 635 lb-ft of torque, be no larger (and preferably smaller) and better-performing—and it had to do all of this at approximately the same cost as the 6-speed.
Going back to the founding of its Hydra-Matic Division in the 1930s, GM has been a leader in automatic-transmission design, and Goodrich’s tight-knit engineering group drew upon the company’s decades of experience, as well as today’s most advanced computer tools, to meet the daunting goals that had been set for them. “We started with a clean sheet of paper,” Goodrich explains, “looking at various power-flow combinations and options, and what was best for fuel economy, what was best for the speed and torque and how we could achieve packaging size that the Z06 required. Meeting those three goals while also doing it efficiently for fuel economy was our greatest challenge. In trying to package and arrange the components, we made extensive use of finite element analysis throughout the development process to optimize for mass. Mass is obviously a key characteristic when you’re talking about a performance car like the Z06. We’ve made extensive use of aluminum and we have a few magnesium parts inside the transmission. We actually have an aluminum gear set and carrier, which is a first for GM.”