Originally Posted by ap72
a stock cast crank is usable past 7,000 rpm, BUT you need to properly machine and build your engine and use the lightest rod/piston assembly you can.
Losing weight on your rotating assembly goes a LONG way when you start going into higher RPM. The same holds true for your valve train.
I have seen plenty of broken cast cranks in 375 horse circle track engines over the years that turn up to 6000 RPM.