What causes power to shift to higher RPMs?
 

More specifically, what causes the power to be higher up on an s5 engine? Is it the intake, the higher compression, or a combination of both? When I rebuild my engine I plan on using s5 rotors and was wondering how this would effect the placement of the power band.

Compression is one, but the major increase was the redesign of the intake system to include tuned chambers and variable runner length. This greatly affects the characteristics of the torque/hp curve.

Good, I was hoping that wouldn't put usable power past my rev limiter. Basically, I have a friend that is pulling his engine (s5) to drop in a V8, and he said he would give me the engine. I still debating on wether to swap on the s5 manifold to get the VDI or not, but I doubt I will.

If you do put the intake manifold on the increase in power is GREAT! The power band stopped at around 7500, somtimes further on cooler days on my car.

You could just do that untill you swap the s5 motor in. I would think you would need the ECU and harness. I dont know for sure though.

S5's have like an 8800rpm rev limiter don't they? But the power still falls off way before that.

I would think that a street port and a header would affect the powerband much more than s5 rotors, correct me if I'm wrong. I've got s4 rotors in my 88 but the car keeps pulling past 7000, and kinda levels off (partially due to a fuel pressure issue I think). I managed 172rwhp.