The highest horsepower car for sale in the history of General Motors at a whopping 638 is in itself a beast. Add American Racing headers and a smaller Lingenfelter supercharger pulley and snout and suddenly the Corvette ZR1 is just plain scary. It's not only how hard your neck is snapped back, but how long it takes to get back to vertical. Some call it a butt dyno when guessing horsepower but in this car its a head dyno because its so fierce. The owner, Ben Treynor, is a familiar name among fans of modified performance cars. His Renntech Mercedes S600 was profiled in the October 2003 issue of Car & Driver magazine. From a Supra Twin Turbo, multiple Vipers including what might be among the first (or first widely known) over 1,000 horsepower in a modern car. A previous owner of an 2006 Corvette Z-06 with LG Headers, he can attest to its disconcerting rear suspension movements and being nearly undrivable due to the excessive sound in the cabin from thin-walled exhaust headers. His