i had a quick read of the sport RWD class rules and they appear to be pretty good on the whole, but the weights listed for a turbo, ie single power adder, 6cly was around 1450kgs when converted from memory, now this is above what a stock gtst will weight, 32 anyway without any form of lighting (i dont need to aircond or a stereo anymore) so thats ione thing i would look at, around 1200kgs would be more appropriate