Steve Temple
July 1, 2006

Flogging more performance from your ponycar doesn't require a lot of heavy breathing. Sometimes all it takes is a little extra brainpower. No doubt you've noted from this issue's "Supercharger Slugfest" cover theme that there are a lot of good air pumps out there. Each type has its virtues, but that's only half of the story. Without precise computerized fuel management, at best you'll run rich and lose power, and at worst, you'll toast an engine if the mixture leans out.

Supercharger companies handle the software aspect in a variety of ways, but Whipple feels it has a leg up in this area. That's because when Ford asked the company to develop a twin-screw blower for its aftermarket division, Ford Racing Performance Parts, as part of the deal Whipple received some Blue Oval "engineering support" (those precious codes for the engine computer). Not only that, according to Whipple, Ford did a great deal of on-road testing of the supercharger in a wide range of temperatures, elevations, and load conditions.

So when it came time to calibrating the computer to compensate for increased boost, Ford had already tackled that thorny issue. That meant Whipple didn't have to tinker around with any custom programming or reverse-engineering (which can be a hellishly tedious job, especially when factoring in the electronic throttle and transmission, and their torque-management functions). All that testing and tweaking has already been done, and the Ford software downloader automatically adjusts the injector pulses and timing for changes in the boost level, camshaft, and exhaust system.

Going to visit Whipple was like a trip to Wet 'n Wild. The twin-screw supercharger kit comes complete with everything you'll need, including a Ford Racing-sourced computer tune.

Enough of the brainiac stuff, though. Just how much power did we see at the wheels with Whipple's new '05-up Mustang kit? With 10 pounds of intercooled boost (using a 331/48-inch pulley and 91-octane gas), the output peaked at 489 hp and 447 lb-ft of torque at the wheels. That's an increase of 224 horses from a baseline of 265 hp. With a slightly smaller, 311/44-inch pulley producing 11 pounds of boost, the dyno readout was 504 hp and 469 lb-ft of torque.

How hard is it to bolt on the blower? As you can see from the accompanying photos, it goes on the engine with a minimum of fuss. For the average DIYer, figure on spending most of a weekend to pull off the stock intake and manifold, add the extra heat exchanger and water pump for the intercooler, and attach the blower case and related accessories. In an effort to meet the deadline for this special issue, the unit we checked out was actually a prototype, so some items on the production version will actually be refined even further for ease of installation (with prefitted gaskets, for instance). One feature that makes the install easier is the self-contained oiling system, so you don't have to tap the oil pan.

For those not familiar with the twin-screw supercharger, inside Whipple's 2.3-liter blower case is a pair of intermeshing aluminum rotors, one male and the other female. The male is identified by its three bulbous lobes, while the female usually has five valleys.

The twin-screw setup operates in three phases: inlet, compression, and discharge. During the inlet phase, as the lobes of each rotor pass by each inlet port, air is trapped between consecutive lobes and the cylindrical casing. This air then moves axially (forward) throughout the case and fills the inner-lobe space between adjacent lobes.

As the rotors mesh, the air is trapped between the rotors and the casing. Continued rotation progressively reduces the space occupied by the air, causing compression. This compression phase continues until the inner-lobe space becomes exposed to the outlet port, where the air discharges into the intake manifold.

Whipple points to several advantages of its twin-screw system over the traditional Roots type, such as reduced temperature, less parasitic loss, higher efficiency, lower noise levels, and a flatter torque curve with no fall-off in power at the top end (as proof of the latter, check out those power curves on the dyno sheet). The company also notes that a centrifugal blower just can't match the throttle response of a positive-displacement, twin-screw unit.

Whipple now builds its blowers completely in-house to minimize backorder problems. After experiencing delays from its overseas supplier of screw compressors, the company decided to do the operation itself and develop an entirely new lineup of superchargers with the latest technology in rotor profile and coating, along with the design of the housing and bearings. Whipple says these changes resulted in less noise, greater reliability, improved durability, and the ability to update and repair the system.

As for the bottom line, cost of the Whipple package ranges from $4,500 to $6,289 (the prices go up when you add intercooling and polishing of the components). Considering how much power you get per dollar, those are big results from a modest amount of effort. If only pumping iron in the gym was so easy.