haha, well yeah, you're going to need ALOT! even though there is no NOS involved, you have to understand that the GTS has a pretty high compression ratio...because of this, you need to really do some work on the internals to strengthen your engine before it can take the added power and stress of a Turbo.
1) I'd go to www.monkeywrenchracing.com
and pretty much buy every part they have to build up my internals (rods, lower compression pistons, etc.)
2) I'd get a better braking system, probably a big brake kit (AEM
or brembo) because if you're gonna be going fast, you need to be able to stop, hehe.
3) I'd just overall improve everything else on the car as in tires (you're gonna need some better traction if you want to utilize the power best), lightweight parts (Hood
, rims), etc...if you're going to put in the money to get a t4 Turbo, you really want to free up all the hp. you can from your car...
our cars (especially the GTS) are not made for Turbos, so to strap a Turbo on them, you really have to know what you're doing because it's a big step...just definately have someone who knows exactly what they're doing guide you...
just my .02