Dan_Soprano said:
That's not completely accurate. Modern Roots style blowers utilize a pair of "lobes" that have improved quite a bit since the original Roots blowers were introduced. The early Roots blowers utilized a 2-point strait cut lobe and no bypass system. The most recent Roots Hybrids utilize a 3-point design that have been twisted to promote efficiency. (They look similar to a piece of licorice). These lobes actually paddle the air from one side of the case to the other, where the charge is compressed within the intake manifold.
Screw blowers as already stated utilize a set of rotors that resemble giant screws that compresses the air directly between one and other and compression actually takes place within the compressor itself. Their level of efficiency is notable at higher bloost levels, since they aren't prone to leak down like a Roots design is, but since compression is always taking place, ACT's tend to be elevated at lower levels of boost because as we all know...compressed air gets hot. The end result, Twin Screws run cooler up high, and Roots blowers run cooler down low.
...and I wouldn't put a whole lot of faith into KB's advertising propaganda. It's more creative reading, than accurate Tech. Take it with a grain of salt.
Also, as far as the KB vs ATI debate goes...assuming we’re talking about two equal blowers here (a P1SC and a 1.7LKB) the bottom end torque difference between a Procharger and a Kenne Bell are very similar to one and other. True, the Twin Screw does hold a slight advantage, but most of that is on paper. In the real world, that little bit of an advantage the Twin Screw holds at the very bottom end, usually ends up going up in tire smoke anyway. After that first few hundred RPM, the Procharger is going to prove every bit as hard hitting down low as the Twin Screw. The Prochargers 4.10 gearing and standard cooler put it right on part with the KB's at all power ranges…and perhaps even a little further ahead on the top end.
As far as him being "better off" with the KB or the Procharger in comparison to a Eaton based Roots design.....perhaps from a maximum horsepower standpoint, but the REV II AED kits for the 99-up GT is every bit the blower either of the other two are and will run right up there to the 350-400rwhp range with either of them. After that, the MP90S the Allen kit utilizes has pretty much run out of steam.....but considering it's the smallest displacment blower of the three, this stands to reason. But again, that's not to say it isn't a quality built kit, with top notch craftsmanship. What it lacks in peek horsepower, it makes up for in drive ability and reliability. Power aside, the other blowers have yet to proven a match respect with regards to the durability of an Eaton.
And that's just from the Ford and GM camps. Auto manufacturers picked this blower as OEM for a reason ya know. 
. And yes go with 3.73's.
