what should be the first things I should do to my r53 to gain hp?

 

Change the SC pulley to a smaller unit, 15-17% reduction and cooler plugs.

 

You'll also need a smaller drive belt. Some special tools are needed, pulley removal tool and belt tensioner bar.

If needed contact Way at Way Motor Works for parts and tools.

Much less benefit from air intake or exhaust (more weight savings and louder sound)

Next thing is not HP but reduce weight of wheels and move from runflat to non runflat tires. Max Summer tires are good for warm weather and street use but wear faster than All Season tires.

Ultra High Performance All Season tires are a compromise for colder weather and street driving without loosing good handling.