Turbo is an interesting thing. It has a range of optimum RPM that give maximum boost. Any faster, it will lose the efficiency and no longer maintain the boost pressure. It is always spinning as long as there is exhaust gas flowing pass it. Then, there is waste gate, twin scroll design, VGT, blow off, mis-firing system etc. Maintenance wise, some engines have design flaws that would cause EO trapped in narrow passages to be cooked under high temperature, creating sludge. As an owner, this is something I'm especially hoping not to see on CFE.

About turbo engines and sludge, believe it or not, the Audi/VW 1.8T first generation cars are especially famous for this. The thought of me almost buying one of those is enough to give me nightmare.