Modifying N/A cars to forced induction is all OK in the short term. However, expose them to extended trackwork and as Gorilla said, they soon generate heat and stresses the car is not designed to cope with. Not just engine but gearbox's, diff's and all sorts of other things start to go wrong.
Put a S/C CSL/M3 up against a CSL on one or two laps and it'll probably toast the std car. Give it death for 8 or 9 lap sessions all day at Spa in 25 degree ambients and see which car is still out there having fun at the end of the day?
Give me a bog standard drivetrain with stronger brakes, proper tyres, sorted suspension and good geo all day long.
