As long as the tune is safe with low timing he should be fine, but an intercooler or meth is definitely the prefered route for longevity and will make getting to 400 easier. The Si is a little more efficient than the S and SQ. I remember years back a local guy made 429rwhp with his non intercooled Si at almost 13psi. Engine survived a few years before he sold it. His setup was a 3.33 pulley and powerpipe. Believe it hit 12.8psi. Without an intercooler or meth the car will just be severely down on power once that blower heat soaks.