Don't listen to this guy. Roots blower compliment the power characteristics of the non PI motors better than centrifugals.
This year I've had BOTH of the following combos (Note all dyno numbers are MUSTANG dyno, not dynojet):
OLD:
98 2V (non PI) with SVO roots blower
stock headers
Off Road H pipe
11lbs max boost
280rwhp 310rwtq
CURRENT:
ENGINE SWAP 02 PI 2V with Voretch SQ
BBK LTs & off road X
Steeda Boost pipe
11lbs max boost
367rwhp 367rwtq
Without PI heads, you won't be able to take full advantage of the top end power that a centrifugal blower makes. So you be near the same rwhp as my old combo, but your low end torqe will be severly lacking in comparison. Hell, the low end of MY new combo is lacking in comparison. Granted it screams on top, but again that is due more to the breathing capability of the engine itself.
With my SVO, I beat several
vortech'd 96-98GT's and even a vortech'd 5.0 AT THE TRACK. I outran C5's and Lightnings on the street with no problem. And on top of that, full boost at 2000 rpm is hard to beat.