4LT GS RoadsterWhat 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.
ZR1 Eaton Supercharger - Vette Magazine
