the problem is that stresses on components like valves and pistons are related to the rpm squared. The accelerated wear on bearings is linear, or close to it if you don't have oil issues. This is why engines have trouble getting into the higher rpms. 10k is about the limit for steel parts. In a lower-powered, super light engine like a crotch rocket, you can bump that up a little, but in a car like ours you would need to upgrade every reciprocating part to be about as good as you can get (light and strong - low weight minimizes the force as well) with steel before running 8k or more.
