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Corvette Magazine :: Overachiever : 2015 Z06
For rest of the article, with many more pictures, and specific sections entitled, "Transmission: Eight Is The New Six"; "Exterior Design: Downforce Producer"; and, "Final Words: Waiting Game, please see following link.corvette-mag said:Overachiever:With a supercharged engine, ultra-wide tires and downforce-producing bodywork, the 2015 Z06 sets a new standard for Corvette performance—while offering the convenience of an automatic transmission and the open-air fun of a lift-off top.
When the 2014 Corvette Stingray was unveiled last year, nearly everyone’s attention was focused on the car’s somewhat radical styling; its new, more powerful engine, stiffer aluminum chassis and host of sophisticated, driver-oriented technologies played second fiddle. As soon as the media got behind the wheel of a C7, however, the focus shifted to the new car’s driving experience. In short order it became abundantly clear that the new Stingray delivered performance on par with the sixth-generation Corvette Z06. This was a crystal-clear omen that any higher-output edition of the C7 would utterly rock the sports-car world, which is exactly what happened when Chevy rolled out its 2015 Z06 at the Detroit Auto Show. This supercharged tour de force out-performs all previous Corvettes, including the C6 ZR1—which is exactly what Corvette Chief Engineer Tadge Juechter challenged the members of his team to achieve.
Engine: Blown Away
The heart of the Z06 is a supercharged 6.2-liter V8 that generates an estimated 625 horsepower. John Rydzewski, Chevy’s Assistant Chief Engineer for Small Blocks, explains how this powerplant, dubbed the LT4, ended up being supercharged—something that’s never been done to a Z06 engine before. “We were looking for a higher-output engine to meet the objectives for what Tadge Juechter wanted in the Z06, which was the performance of a ZR1 with an engine that’s as compact and efficient as possible,” says Rydzewski. “We looked at several different options for how to do this, from a naturally aspirated, large displacement, ‘spinner’ engine to various methods of boost, and we determined that the best solution is a compact supercharger design on the existing LT1. This was the most elegant solution because it was least disruptive to the existing vehicle.”
In order to minimize changes to the C7, the Corvette team needed a supercharger compact enough to fit under the standard hood, yet potent enough to reach their power targets. Such a supercharger didn’t exist, so they worked with supplier Eaton to create one. The newly designed R1740 TVS is 10 mm shorter and 10 mm smaller in diameter than the LS9’s supercharger. As a result, the LT4 is only 25 mm taller than the LT1.
Though design changes such as different rotor spacing and higher speed—the R1740 TVS spins up to 20,000 rpm, 5,000 more than the supercharger on the LS9—yielded greater efficiency, the smaller supercharger does squeeze less air than the larger unit used on the LS9, 1.7 liters of air per revolution instead of 2.3 liters. Emblematic of how Chevy engineers tackled challenges throughout the new car, Rydzewski’s team stretched their thinking to find clever ways to extract more power out of a smaller package.
“We needed to minimize all of our losses to meet our power objectives with less boost,” reports Rydzewski. “We worked a lot on the airflow path coming into the engine, with computational flow dynamics, with a lot of iterations, and we came up with a very efficient flow path going into the supercharger. We also developed an improved discharge port that minimizes turbulence, reducing heat and speeding up airflow through a more efficient intercooler and into the engine.”
While the LT4 employs the same cylinder case as the LT1, it uses a number of unique parts to handle higher cylinder pressures. Explains Rydzewski, “We added titanium intake valves expecting that the customers who use this would race it and spin it a lot at high speeds. We also added stainless-steel cast exhaust manifolds to handle the added heat; we modified the cam, adding a bit more duration on the exhaust side; and we went with improved, forged pistons.”
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.
Corvette Magazine :: Overachiever : 2015 Z06