|
I’m going to go with valve train and then rotating mass to strength ratio are the mechanical limitations. Even these 4 valve heads are airflow limited given that it doesn’t make the power it should for the RPM.
Valve springs, rockers, light valves and good rods with the correct oiling and supporting modifications gets you to 9k with a shorter stroke crank and 2 valve heads.
996/997 RSR go to 9000 and a lot higher on over revs with largely the same bottom end. We used to see 11,000 rpm over revs with the engine surviving on 996 and 997 Cups.
Stiffer case and crank are never going to hurt.
|