While the power numbers alone confirm the blower hierarchy, here's additional information provided by another form of dyno testing: namely, a blower dyno. What is a blower dyno, you ask? Just as it sounds, the blower dyno is used to evaluate superchargers without regards to the engine. On the blower dyno, the superchargers are mounted to a test fixture and spun using (in this case) a 400hp V-8 LS-series GM engine. The blower dyno allows Kenne Bell to regulate all of the variables to properly evaluate the supercharger, namely blower speed, air temperature and pressure into and out of the blower, and the parasitic losses associated with driving the blower. That's why such a powerful drive motor is required.
While it doesn't compare to the 500 hp required to drive a Top Fuel Roots blower, some of these larger street/strip superchargers required as much as 150 hp to spin them at 18,000 rpm and 20-plus pounds of boost. Not surprisingly, results from the blower dyno correlate perfectly with the chassis dyno. Configured to produce 20 psi of boost (a level not attainable with the TVS on the 5.4), the TVS checked at 18,000 rpm, 340 degrees of discharge temperature, and a whopping 147 hp worth of parasitic drive losses.
 After running the TVS, on...  After running the TVS, on went the Kenne Bell 2.8-liter H-series blower, which included the free-flowing inlet, twin 75mm throttle body, and necessary Boost-A-Pump to deliver enough fuel to support its power potential. |  Running the same 2.59-inch...  Running the same 2.59-inch blower pulley, the Kenne Bell blower produced 788 hp. |  Part of the success of the...  Part of the success of the Kenne Bell supercharger is the attention to detail-namely the induction system ahead of the blower. This Mammoth intake manifold flows a whopping 1,800 cfm. |
This means it took 147 hp to drive the TVS supercharger at this speed and flow level. By comparison, the Kenne Bell required only 12,700 rpm to produce the same 20 psi. Running the same boost level, the discharge temperature registered only 282 degrees, and the Twin Screw blower absorbed only 111 hp in the process. Thus the Twin Screw reduced the inlet charge temp, blower speed, and parasitic losses required to reach the desired boost level.
Certainly it would be interesting to compare the Roots and the Twin Screw in the exact same displacement and with equivalent aero-restriction inlet systems to see the similarity of the numbers, but for now, Kenne Bell's test provides an interesting look at two of the popular upgrade options for GT500 owners as available. Either one has the capability to provide more power than your average driver is really equipped to handle, but for those who find too much is just right, now you're better educated as to how these two options compare.
Popping The CorkOne of the often-overlooked aspects of any supercharged engine is its induction system. Unfortunately for enthusiasts, positive-displacement superchargers are ultra-sensitive to inlet restrictions. Lucky for us, it's actually easy to determine whether the inlet system (basically anything in front of the spinning rotors) is restrictive. In the case of the 5.4-liter GT500 motor, a simple vacuum gauge hooked up between the throttle body and supercharger will indicate whether vacuum is present. If any vacuum is present when running at or near the peak engine speed at wide-open throttle, there's a restriction in the inlet system somewhere.
Taking these same readings between the throttle body and mass air or between the mass air and filter will help you know exactly where the restriction is most prominent. Is the restriction in the intake manifold between the rotors and the throttle body, the throttle body, the mass air, the inlet tube, or the filter? Luckily for us enthusiasts, the gang at Kenne Bell has spent long hours on the dyno replete with data logging at each point to determine where the restrictions exist, and then to produce the necessary products to cure the situation.
How much do these restrictions hurt the power output? Replacing the throttle body, inlet air tube, mass-air housing, and filter assembly improved the power output of the supercharged 5.4 from 664 hp to 745 hp. These power gains came with no change in air/fuel, timing or blower pulley size.