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).

The kit itself is complete, meaning everything is there to get the blower on the car, get it running, and make some power. KB offers three versions-6 psi (106 hp), 9 psi (160 hp), and 14 psi (262 hp). We chose the 9 psi version because that is the perfect amount of boost to run on the stock engine's rotating assembly before taking the chance of pushing the envelope and turning it into a taco salad. While it would have been nice to go with the 14 psi setup, that combination is a bit more than what the owner wanted.

Additionally, the kit comes with your choice of a polished or a black-coated 2.1L supercharger (we chose the black version) rated for up to 750 hp. Along with the compressor, the kit came with everything we needed-a bar and plate intercooler, Garrett heat exchanger, billet bypass valve, 36-pound injectors, 90mm throttle body, Kenne Bell Boost-A-Pump, and a tune from Kenne Bell to reflash the ECM and make it work with the supercharger.

Blown Away
Once the installation was complete, the computer was retuned, and everything triple checked to make sure there were no leaks or problems. The Stang was strapped back down to the dyno so we could see just what 9 psi from a Kenne Bell twin-screw would do for this hot rod. The car was fired up, and Chris Winter put the hammer down.

The rollers screamed, the blower whined, and the car sung at full song. Right off the bat, we knew there would be a serious power increase as the car took on a life of its own with a renewed sense of anger flowing from the tailpipes.

Thanks to the blower kit, the car pounded out 385 hp and 414 lb-ft of torque at the rear wheels. We quickly spun the calculators in our heads, and came up with a power increase of 133 hp and 132 lb-ft of torque-at the rear tires! Knowing more power was available at the plant of our right foot, we took the car back to Raceway Park to see what it would pick up in terms of elapsed time and trap speed. While we probably should have thrown on a set of sticky rear meats for ultimate traction, we wanted this to be a true A to B comparison, so we kept the car as it was (rear tires included) for our after testing.

Once again, Smith did the driving duties, and after banging the gears and blowing through the quarter-mile timers, the scoreboard validated our dyno numbers. The red rocket ripped off a 12.54 at 115 mph. The extra power afforded by the blower tacked on 16 mph and lowered the elapsed time an astounding 1.35 seconds. While the 12.54 is a respectable number, the 115 mph trap speed indicates the car has a lot of e.t.'s left in there. A swap over to sticky drag radials or slicks would most definitely aid the car in lowering the elapsed times, as a more aggressive launch and a better 60-foot clocking would result.

When all was said and done, this run-of-the-mill Mustang GT was turned into one superbad Pony thanks to a Kenne Bell twin-screw blower. Who knows, maybe 14 psi, a set of rear meats, and some killer power numbers and track times are in this Mustang's future.