[kenikh]

Think about it - the car is a 3.0L V8. The bore is so much smaller on these cars, so the valves can be smaller/lighter even if the car is the 2V version. If it is the 4V version, no wonder it can rev to 8500RPM - the valvetrain is even lighter! When you are taking like displacement from 8 to 6 cylinders, the bore and valves get bigger/heavier. It is easier/cheaper to spin a light valve train.

As a result, Porsche was astute enough to know not to overbuild their cars for revs they wouldn't need to reach. So if you want to really spin a big bore 911, you need to spend a lot of money upgrading the parts that were not designed for those speeds:

Valve retainers
Valve springs
Valves (sometimes)
Rod bolts
Crank cross drilling

This is where the cost comes in.