Frank H. Cicerale
March 1, 2009
Photos By: courtesy of Crazy Horse Racing

When Ford released the new-fangled modular engine family in 1996, a new chapter in Ford performance was opened. With 4.6 liters and two valves per cylinder, a new wave of performance modifications was soon to come.

Today, the Two-Valve modular engine performance has been largely overshadowed by its Four-Valve and Three-Valve (both naturally aspirated and supercharged) brothers, but nevertheless, the Two-Valve mod mill is quite plentiful out there in Mustang land and there is a lot you can do to up the power.

The inherent problem with the Two-Valve is the fact that with its small bore spacing, going bigger is limited in terms of cylinder oversizing. Obviously the easiest way to make some serious power with a Two-Valve is by throwing on a forced induction setup of some kind, be it a turbocharger, a centrifugal supercharger, or a positive displacement blower.

With that in mind, we decided to tag along as the crew at Crazy Horse Racing in South Amboy, New Jersey, laid a thundering Kenne Bell 2.1L supercharger atop an '04 Mustang GT's powerplant. But before we delve into the main course, let's taste a bit of the appetizer and take a look at what makes the Kenne Bell blower tick.

Twin Screw History 101
Heinrich Krigar in Germany first patented the twin-screw supercharger in 1878, showcasing a two-lobe rotor design. While the configuration resembles a Roots design, the difference lies in the rotor lobe twist, where the twin-screw has an angle of 180 degrees along the length of each rotor. More than 50 years later, Alf Lysholm patented the design seen in the twin-screw blower today, that being an asymmetrical 5-female/4-male-lobe rotor design. In basic terms, the twin-screw blower is a positive-displacement blower that operates by pulling air through a pair of meshing screws (rotors). The intake is located at one end of the two screws. As the screws, or rotors, turn, the air is pulled in from the intake side, moved along towards the exhaust, or discharge side, and compressed during the movement from one end of the blower to the other. Unlike a Roots blower, a twin-screw has internal compression, which can be defined as the ability to compress air within the housing, rather than in the manifold.

The twin-screw supercharger is such a good design, a version of it was banned from the NHRA Top Fuel category. Norm Drazy developed a large screw-type blower using a four-lobe male and six-lobe female rotor design. The blower, called the PSI, is a phenomenal blower. With that in mind, we figured if it's good enough for a race car capable of low 5-second elapsed times with speeds elevated to 280 mph, then a smaller derivative of it, the Kenne Bell 2.1L blower, would be perfect to make some serious power on a Two-Valve mod motor.

A Tolling Bell
The car in question is an '04 Mustang GT equipped with a five-speed manual transmission with the addition of an aftermarket exhaust system. The car was strapped to Crazy Horse Racing's Dynojet dyno, where it cranked out 252 rwhp and 282 lb-ft of torque. To see what that translated to in terms of on-track performance, we cruised to Old Bridge Township Raceway Park for some before testing on the famous quarter-mile.

With MM&FF Editor Evan Smith as the wheelman, the SN-95 motored to a best of a 13.89 at 99 mph. While not bad, we knew there was some serious power potential with this Pony. So it was back to the shop for the installation of Kenne Bell's Big Bore 2.1L supercharger kit for the Mustang.

Kenne Bell has been at the forefront of putting a supercharger atop a muscle Mustang or fast Ford for some time. A Kenne Bell twin-screw has numerous advantages, some of those being relatively quiet operation, and a self-contained oiling system (which means no tapping of the oil pan like some centrifugal blowers).