My old 500bhp engine did 24k miles before a re-build was required. That included 10 Topspeed runs at various events. Performance was tailing off badly at that stage. 183.3 mph at 12k was down to 181.8 at 24k & that included a 50 shot of Nitrous. Inspection showed a badly worn cam & followers & a T4 Turbo that was literally falling apart ( Yes the same Turbo did all those miles.)