Si @ Sitech buzzed his engine a while ago and the datalog showed nearly 10,000 rpm without the crank letting go!

I'm planning to rev mine to between 8500rpm and 9000rpm - that's on a lightened, knife edged and balanced ST170 crank.

In all honesty, i'm not sure the ST170 crank is any different to a normal 2.0 Zetec one - i think the differences are in the rods and pistons.

You can run around 300/300 on the standard ST170 internals - first thing that'll let go is the ring lands!