the XS kit doesnt cause as much "stress" as people think. what happens is the kit fails. sometime the manifold cracks, sometimes one of the bolts they put inside the tubing comes loose and gets sucked through the Turbo, along with numerous other things that can happen. I have yet to see the motor fail from 9 lbs of boost.
The SF kit is much more reliable. This means he wont have to worry about how to detune the kit. Something XS does on most celicas. I've seen 2 people now be detuned cause of poor tuning/performance of the xs kit. I severely dislike the company and their product.
thats all I meant. lol