i have a 05 wrx with stromung turboback. I was wondering if adding a vishnu pulley set is worth it? does it gain any power?

 

A vishnu pulley set adds some power at the wheels (estimated 5-8 whp) by reducing drivetrain loss. Not hugely noticeable, and some people don't like them. They slightly underdrive your alternator, so your lights might dim a bit, and I have found that I have more clutch shudder since I put mine in.

For the price, not a bad upgrade, but I would go for engine management if you don't have that yet.