Originally Posted by Karl

The ability of a turbocharged engine to rev to high rpm's is based primarily on two factors.

1. strength of engine which also encompasses design to be correct for such an application

2. Ability of the engine and turbo to flow sufficent air at these rpm's in order to maintain torque. (this is what makes an engine feel revvy)


The reason the turbocharged ZVH normally suffers with holding high rpm torque is its rated capacity in comparison to the cylinder head flow rate. Essentially this means that the head itself becomes a flow restriction in relation to its capacity and hence engine torque falls quite rapidly with rpm. This can be overcome to some extent with a larger turbo and heavily reworked head which can help increase engine breathing at higher rpm's but this does of course lead to the usual lag, drivability and most importantly cost issues that come about in building an engine capable of using such a large turbo!

hope that helps explain things a little!