Don’t be fooled by KB’s creative marketing techniques. Twin screws are only more efficient that an Eaton blower when you really start putting the boost to them. They may thrive at 14psi, but they’re the worst of the bunch with respect to “efficiency” at 6-7psi! In fact, the KB’s makes far more heat than a comparable M112 and even more so than an M90 at or below this level. Roots blowers are designed to “paddle” the air back and forth within the housing in order to build compression. Not very efficient from a volumetric filling standpoint, but it beneficially keeps discharge temperatures to a minimum. It is true that Adiabatic Efficiency with the Eaton’s starts to rapidly take a nose dive after the 6-8psi level (depending on the blower), but the efficiency of the M112 is in the 65% @ 7-8psi and 65% @ 4-5psi with the M90.
The screw compressors like the KB and Whipple uses an internal compression method, which is typically a 1.35 ratio on Lysholm and Auto Rotors. This means that it’s able to move a larger volume of air in the lower ranges, but not without spoiling most of the charge with elevated discharge temps. The screw design works by constantly compressing air even when it does not need to. Squeezing and discharging hot air repeatedly, over and over. Adiabatic efficiency at 2-psi is in the 30% range. At 4-psi it is in the 40% range. Peak is 65% at 15-psi. Great if you’re really planning on putting the boost pressure to your engine, but not so great if keeping a stock motor together is your priority. If the Twin Screw design was in fact a superior design, why are 90% of all automakers still utilizing the Roots based Eaton blowers? Stone reliable and more efficient in the lower regions, that’s why. Sure the Ford GT uses a twin screw, but that’s also because it’s pumping out at a whopping 12-13psi through it’s housing which is right around peek adiabatic efficiency for that particular blower. Not to mention it was designed to fulfill the needs of a 5.4L 500rwhp super car, not a measly “keep up with traffic 300hp Mustang!” The Twin Screw wasn’t used because it was a “superior blower”, it was utilized because it was the best choice to get that particular job done. And lets face it, you have to use the right tool, for the right job…right? But pulley that puppy for 6psi and see how well if performs!
His post suggested to me that money was a concern; otherwise he wouldn’t have stated he wanted to “safely” add power to a stock engine. If money was no object, then he would have opted for a high end rebuild went with as much power as streetable and not have worried about it.