To illustrate the power potential...
To illustrate the power potential offered by the TVS, we installed a 2.59-inch blower pulley. The result was an impressive 609 hp at the wheels. The TVS has become a popular option as it fits under the stock strut-tower brace and doesn't require any fuel system upgrades to increase the power of a GT500.
Factory blower and turbo cars are great because additional power is just a pulley change away. Of course, these swaps require proper air/fuel and timing values that are commensurate with the available fuel octane. The combination of the performance tune and swapping on the 2.59 blower pulley brought the peak power output from 443 to 518 hp. It should be said that additional power is available from the stock M122 blower with a larger crank pulley and modifications to the intake tract (air filter and inlet tubing, mass air housing, and throttle body), but ultimately, it's the blower itself that limits power production.
With the testing completed on the M122, it was time for the Super Snake to receive the TVS blower upgrade. Rated at 600 flywheel horsepower by Shelby Autos, the TVS had considerably more to offer this GT500 motor. With an increase in both displacement (2.3 versus 2.1 liters) and efficiency (see previous description of changes to TVS), it's not surprising that the TVS blower increased the power output of the GT500 motor. By running the same 2.59-inch blower pulley on the TVS blower, the peak boost numbers jumped from 11.5 to 14.5 psi. The peak power jumped from 518 rwhp with the M122 to an impressive 609 with the TVS.
As with the M122, there was likely more power to be had with changes to the air intake and possibly a larger crank pulley. We've seen TVS GT500s, such as Justin Starkey's (of VMP Tuning), make nearly 700 rwhp so optimized. Not everyone can or will crank up the boost to the maximum setting and then make the concerted (and important) effort to minimize inlet restrictions. Positive-displacement blowers (Roots or Twin Screw) are sensitive to inlet restrictions. Check out the short sidebar on inlet system testing, but know that any restriction in the inlet system (basically anything in front of the entry to the rotors themselves) will result in a drop to flow, boost production, and ultimately, power production.
The 2.8-liter H-series Kenne...
The 2.8-liter H-series Kenne Bell supercharger offered increased displacement and efficiency and the ability to produce huge gains on an otherwise stock 5.4.
The final test was to remove the TVS and install the Kenne Bell Twin Screw supercharger. Like the comparison between the M122 and the TVS, the Kenne Bell Twin Screw supercharger was both larger in displacement (meaning more output per revolution) and more efficient (meaning less charge temperature per pound of boost). While individuals and companies alike argue the different efficiency rating of a supercharger, the real test is running them on the dyno. Of course, we also had charge temperature measurements and even test results from Kenne Bell's own blower dyno.
To say that a Twin Screw supercharger is more efficient than a Roots supercharger is hardly news. Every SAE paper ever written confirms this fact, and the real reason OEMs use the Roots blower is that it provides an excellent combination of power, reliability, and cost. Basically, it does the job of reaching the desired power level (usually not terribly high on a production vehicle) at an attainable cost and with quiet execution. Were maximum power the design goal, you'd quickly see a change to the Twin Screw design. Nowhere was this more evident than the use of the Twin Screw on the (cost-is-no-object and higher horsepower) Ford GT. Further illustrating the efficiency and size advantage held by the Kenne Bell supercharger was the fact that removing the Eaton TVS and replacing it with the Twin Screw resulted in a jump in power to 788 hp using the same 2.59 pulley. Boost production jumped from just 14.5 psi with the TVS to 23 with the Kenne Bell.