How close are they to the street cars? What kinds of modifications are allowed?
The Porsches are reasonably close to stock. All 996 and 997 start as street cars. The interiors are stripped and custom roll cages are welded in. The minimum weight is as high as the street car, so interior removal is more for fire safety than for weight savings. The only legal modifications to increase power are an airbox, ECU re-flash, and exhaust after the stock header. The transmission is stock, except that a better differential can be used. Shocks, springs and sway bars are free, and some of the rubber bushings can be replaced with plastic (no monoballs). The lower control arms and toe links are GT3 parts. The stock fuel tank is also retained, but the volume is displaced down a bit and a single dry-break and discriminator/vent valve are added. All of the windows are glass, and many of the climate control components are even left in place. The Mustangs and many BMWs are not built from street cars, but rather they are built up from a caged tubs and feature fewer production car parts
