HP gains are smallish, espically for the amount people want to charge for these.
Resizing won't mess up your timing. There are basically three pulleys you can replace:
- Crankshaft pulley - basically the same idea as a lightweight flywheel - this is purely a racing application, though, as the added vibration from losing the counterweight will shake things too much and can cause long term engine damage.
- Alternator pulley - just ends up lowering the voltage in your car. The electrical system will use a certain amount of power somewhat independently of the voltage, so its really not worth it. It can cause electrical system problems also.
- Power steering pulley - OK you can make a difference here, probably about a HP or so (1%). Maybe 2.
Running non-standard sized belts is no big deal.
The problem is that the manufacturers charge an arm and a leg for these things. I'm wondering if you can't find a large pulley somewhere that will mate to the existing spindle on the P/S pump and just make your own.