What happens when you apply military-spec engineering to an automotive project? A nuclear-tipped, road-hugging cruise missile, that's what. Of course, creating a high-caliber, 760hp Corvette takes some serious brainpower-just throwing on some wings and things won't give a Vette a ballistic leap in performance. No, you need a company like Pratt & Miller Engineering, a full-service concern that specializes in design, development, and manufacturing for the motorsports, OEM automotive, aerospace, and defense sectors-a potentially explosive synergy, to be sure.
To light the fuse on the weapons payload of its latest Z06-based C6RS Corvette, P&M sought assistance from Brian Thomson of Thomson Automotive, who does a lot of development work on engine blocks for General Motors. Rather than trying to custom fabricate a new supercharger mount for a 6.2-liter LS9 crate engine, Thomson felt P&M could achieve prodigious output more efficiently and cost-effectively by using the 7.0-liter LS7 block as a foundation, and then adding on the LS9 intake and heads. That way, the ZR1 Eaton supercharger would fit right on-no fuss, no bother.
Of course, bolting on a blower case was the easy part. Optimizing the air /fuel mixture was the real challenge. To increase airflow from the puffer to match the increased cylinder displacement, Thomson reduced the size of the pulley so it would spin at 18,000 revs-2,000 more than on a stock LS9. He also richened up the fuel ratio by throwing on a set of bigger, 65-pound injectors, which required increasing the flow from the pump. Lastly, he switched out the factory E40 engine computer for the LS9's E67 unit, which provides a fatter fuel map.
Given the 10 pounds of pressurization (the same as on the LS9, but feeding a bigger volume of 427 cubes), Thomson went to Diamond Racing for a set of Teflon-coated, forged-aluminum, ceramic-topped pistons, dished to lower the compression ratio from 11.6:1 to 9:1. Fitted with bigger rings to prevent blow-by and oil consumption, they spin through a bore and stroke of 4.125x4.000 inches. The LS9 heads didn't need any porting, considering the final dyno numbers, but they were equipped with 2.16-inch titanium intake and 1.59-inch Inconel exhaust valves.
The result? An explosive 760 horses, along with an outrageous 830 lb-ft of torque. Although turning the blower faster (Eaton admits it can spin as high as 20,000 rpm) or swapping cams would unleash even more power, Thomson feels that would be overkill. As it is, there's more than enough impact at ground zero to make everybody run for cover.
But we didn't duck into the bunker when this bomb landed, paint still drying on the blower case, at Mid America's Funfest in late September. We took aim with both camera and a deft foot on the throttle (well, stomping with our clodhoppers, actually), and started shooting at anything that moved. Turns out we were the ones really moving, as the traction control struggled to keep from being overwhelmed by an exquisite excess of power. We whipped around the placid farmlands of Effingham, Illinois, like we were impossibly late for a cornhusker's convention. Farmhands dropped pitchforks and cattle stopped in mid-chew as we whooshed by like a prairie tornado, a screaming yellow zonker scorching the local landscape.
The hot mill is only part of the C6RS story, though. Pratt & Miller incorporates other aspects of leading-edge R&D from its Corvid Technologies division. Based in the heart of stock-car country in Mooresville, North Carolina, this firm exemplifies P&M's scientific approach. Although initially conceived to bring state-of-the-art engineering and high-performance computing to competition cars (supporting a variety of GM Racing programs in the ALMS, SCCA, Grand-Am, and NASCAR racing series), Corvid also provides proprietary services to military and aerospace clients such as the U.S. Navy's Aegis Ballistic Missile Defense program.