2007 Genaddi G-SPT

Perhaps Mark Gerisch had an affinity for saws or guillotines while growing up because as an adult, Gerisch, the man behind Genaddi Design Group of Green Bay, Wisconsin, likes ripping off the roofs of expensive American musclecars. Two years ago, he scalped a Ford GT and came away with a GTX1, a roadster version of the hardtop-only supercar, not to mention a nicely done, modern interpretation of the 1966 Le Mans race car. We drove one and were impressed by the ingenuity and execution of its design (April 2006).

So when Gerisch informed us he had a new topless toy, a Z06 convertible, aka Genaddi G-SPT, we were eager to see if it would be as stirring as the GTX1.

Why a drop-top Z06? "The premise for doing the Z06 convertible," says Gerisch, "was simply to show GM and the rest of the world that the Z06 they said couldn't be built in fact can --- and with most of their own parts." Thus, by removing the Z06's roof and installing the power-folding softtop from the standard Corvette Convertible, Gerisch makes a fine play at convincing Lutz and Wagoner that Chevy need look no further for a new product planner. Of course, removing the top from a fixed-top equation never equals extreme stiffness, so, like any self-proclaimed "master coachbuilder," Gerisch went to the drawing board. "What makes it possible is the Structural Chassis System I designed. It's made of lightweight carbon fiber and aluminum, and most of it attaches to the bottom of the car with 3M structural adhesive and 3/16-inch rivets."

According to Gerisch, the SCS, which weighs around 50 pounds, not only improves aerodynamics under the car, but also ups torsional stiffness from the stock Z06 coupe's 5000 pounds per degree to 7800 pounds. While we can't verify these claims, we can attest that, during our drive over Malibu's twisty roads and L.A.'s freeway expansion joints, the G-SPT exhibited coupelike robustness, devoid of the cowl shake that can plague convertibles. Unfortunately, the SCS also reduces ground clearance--at one point, we nearly high-centered the G-SPT going over an ordinary speed bump--and the front spoiler routinely rubs its chin on driveways.

For the G-SPT, Genaddi bolted an SV1 Pro Charger and intercooler to the LS7, which it claims produces 620 horsepower with just two pounds of boost.