Stephen Clark
July 1, 2008

Horse Sense: Unfortunately, we can't always do these stories on our own cars, but we often rely on the kindness of others. Fortunately, Larry H. Miller Ford allowed us to borrow this 3d Carbon-equipped GT for our testing.

In today's performance world, a Mustang owner has a wealth of performance upgrade options from which to choose. When it comes to power adders, nitrous, superchargers, and turbos are all on the menu. To further complicate things, there are centrifugal superchargers and positive-displacement blowers that offer rpm-swelling power or instant boost, respectively.

With the airbox removed, there's plenty of space to mount the supercharger.

If you're a fan of beltdriven power adders, there's another new option coming to light. The Rotrex blower is a centrifugal supercharger that basically uses the intake side of a turbo to produce boost and is turned by a unique traction-drive system. The traction-drive planetary is based on the same theory employed in an automatic transmission.

The Rotrex traction drive setup ranges from 13:1 on its smaller units to 7.5:1 on its largest unit. This produces impeller speeds of more than 200,000 rpm, while the largest unit still spins at 90,000 rpm. Since the supercharger spins so fast, the unit can be much smaller than other centrifugal superchargers and still produce the same amount of boost. The planetary/traction system requires less horsepower to turn than a conventional centrifugal blower and much less than the Roots-style/twin-screw blowers.

Beginning with a stock '07 Mustang GT equipped with 3d Carbon exterior modifications, Forced Air Performance R&D technician Abe Carter begins removal of the air intake pipe and airbox. The front bumper is also removed, which makes the car much easier to work on and allows us to mount the intercooler.

The technology behind the Rotrex blower has been around for years. Forced Air Performance is a new Danish company that has produced superchargers for several OEMs, including the Koenigsegg CCXR, dubbed the fastest production car in the world. Forced Air Performance is a spin-off from the parent company Mountain Performance. MPI produces supercharger kits for snowmobiles and side-by-sides.

"We've had great success with our kits using the Rotrex blower on off-road applications," says Forced Air Performance CEO Mac Randolph. "We chose the Mustang for our first automotive kit because almost every supercharger manufacturer makes a kit for this vehicle, and we want to show off our technology. This will be an excellent opportunity to expand our business into the musclecar market."

After hearing about the Forced Air Performance kit, we were immediately curious as to how it would fit on the car, the type of performance that the Rotrex supercharger could produce, and above all, the driveability. We took a trip to the Forced Air Performance facility in Draper, Utah, to witness the installation of the company's kit on an '07 Mustang GT.


On The Dyno

  BASELINE FAP ROTREX DIFFERENCE
RPM POWER TORQUE POWER TORQUE POWER TORQUE
2,250 108 253 108 253 0 0
2,500 120 253 125 262 5 9
2,750 130 248 146 278 16 30
3,000 141 246 163 285 22 39
3,250 163 264 188 303 25 39
3,500 183 275 219 329 36 54
3,750 197 276 243 340 46 64
4,000 211 277 274 360 63 83
4,250 223 276 299 369 76 93
4,500 231 270 317 370 86 100
4,750 230 254 337 373 107 119
5,000 241 253 354 372 113 119
5,250 243 243 370 370 127 127
5,500 N/A N/A 386 369 n/a n/a
5,750 N/A N/A 402 367 n/a n/a
6,000 N/A N/A 404 354 n/a n/a

With the Forced Air Performance kit installed, we took the car to Gillett Diesel to test the horsepower and torque output on the MD-250 dyno. All dyno testing was performed at 5,000 feet above sea level, so the horsepower numbers are about 20 percent lower than what we would've seen if this testing were done at sea level. All the horsepower and torque numbers are actual and not corrected for altitude. For the sake of comparison, we also brought along a stock '08 Mustang GT and an '07 Foose Stallion Mustang that has a competitor's 12-psi centrifugal supercharger kit.

On the dyno, the Forced Air Performance Mustang produced 401 hp at 5,750 rpm and 377 lb-ft at 4,800 rpm. We made four back-to-back runs to prove the kit's consistency and immunity to heat soak. The first run was 399.5 hp and the fourth run was 401 hp. While the stock Mustang was nearly this repeatable, the other supercharger kit lost almost 10 hp per run for a combined decrease of 35 hp between the first and fourth runs.


Road Test
Even being a mile high, we couldn't knock the wind out of this Pony. With 400 rwhp, the Mustang was fast on the road with incredible lo-end pull. compared to the other centrifugal blowers on the market, the Rotrex blower is smaller and spins much quicker (around 90,0000 rpm), therefore it makes the car responsive but still gives good top-end pull. In comparative terms, the Rotrex produces a Roots-style/twin-screw bottom end while still yielding turbo/conventional centrifugal charger top end.

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