Powervalve issue?

[Jakobi]

Originally Posted by barossi73

All the powervalve does is alter the exhaust length.think of it as 2 exh pipes,1 is tuned for low revs,the other for high revs to take advantage of the 'supercharging' effect.previous to pv the pipe was by necessity a compromise resulting in a narrow powerband.
The powervalve is the switch between the 2 pipes,opened by centrifugal force at ?revs.not saying there arent small losses/gains to be had,(i havent explored)
just trying to clarify the powervalve/powerband thing

It offers a dynamic exhaust port, by restricting it with the PV flapper. It's not just open/closed at a certain RPM. The spring also determines the rate at which the PV opens.

As you said though, it also offers a dynamic exhaust effect in that the drum valves are open as the flapper is closed, which increases the volume/length of the exhaust. As the flapper opens, the PV chambers are closed off.

So the whole system works to offer the best results at both ends of the powercurve, but also has a large influence on the nature/flavour of the powercurve depending on the timing and duration at which everything happens.

Ideally you'd want access to a dyno with the intent of getting the strongest spread of useful power at all rpms. By having the PV slam open early all you'll really achieve is a delay in the power hitting hard which may feel faster.