with the crank pulley, you wont get any more power...just the engine will have less rotating mass, therefore revving quicker, and with less lag. it helps on acceleration, since the engine isnt having as much weight to spin up to 6500rpm, it gets there quicker. ive seen several, but the perrin looks to be one of the best made units ive seen. hope this helps.
...yeah, but you gotta at least give them credit for searching and trying to be helpful instead of starting another thread
They're both right. Lightweight crank pulleys decrease rotational mass, allowing your engine to rev slightly faster (we're talking maybe several hundred rpms throughout the powerband which is hardly noticeable) which makes it slightly more effiencnt and technically gives you a little more power that would have otherwise been lost through unnecessary work by the engine to move a slightly heavier piece of metal in a circle... if you can follow that explanation.
I have a Perrin lightweight crank pulley on my 07 WRX and it's honestly more of a $100 (give or take) word that I can list in my mod list than something I can actually feel the effects of - but I'm still happy I have it. I'm also convinced that it won't harm your engine. Hope that helps anybody who might be interested.