Supercharger Gives Boxster a Boost

The short-stroke 2.5 liter water-cooled flat-six pulls strongly from 4000 rpm up to the redline, but below 4000 there isn't a lot of excess torque. Porsche will apparently address this concern with the still-to-be-announced introduction of the Boxster "S". But for those who can't wait, there is a solution that is available right now. And no, it isn't transplanting the 300 hp 3.4 motor from the 996, although that's an interesting (but expensive) idea.

Michael Levitas, a clever entrepreneur and principal of Turbo Performance Center in Glen Burnie, Maryland, has engineered and developed a belt-driven surpercharger kit for the Boxster that he claims increases torque by fifty per cent between 2500 and 6500 rpm and peak horsepower at the rear wheels by 48 percent over stock. Using an Eaton positive-displacement (Roots-type) supercharger, TPC's kit is complete and employs both engineering and componentry that will ensure quality equal to the rest of the car. PML was given the opportunity to inspect the installation and to drive the finished car recently when Lighthill Motors of Palm Springs, California completed the supercharger installation for one of their customers.

One of the more interesting features of the kit is a vacuum-operated intake bypass valve , not unlike the bypass valves Porsche uses on the 930. It allows the supercharger to spin with less drag (and hence, less friction horsepower) at part or closed throttle by allowing air upstream of the throttle plate to circulate without the resistance of a closed or partially closed throttle. The other noteworthy feature is an additional fuel injection system and seventh injector nozzle added to maintain the correct fuel mixture at high power settings. Boost level is preset at a very conservative 4.5 psi (.3 bar) to ensure engine longevity and obviate the need for special pistons. Although this approach favors mid-range torque at the expense of peak horsepower, for the Boxster this is exactly what was needed. Since air-cooled 930 engines normally operate at .6 -.8 bar, it's easy to see the safety margin built into the TPC kit.

Although TPC suggests a 12-15 hour labor allowance for installation of the supercharger, to insure that the close tolerances dictated by the Boxster's engine installation do not create interference problems with the supercharger and its plumbing, it is wise to allow more time, particularly if the technician has not previously performed the installation. In the case of the car PML inspected, it had been necessary to perform some additional but minor modifications to ensure correct fitment of the supercharger and its ductwork. Turbo Performance Center provides excellent installation instructions and as much technical support as needed.

The finished product was well worth the extra trouble. Zero-to-sixty times dropped consistently below six seconds, and the quarter mile came up a full second faster, at 14 flat with a trap speed of 99 mph. This particular car was shod with Ruf 18 inch alloys and Bridgestone S-02's, so it stuck like glue, at least until you opened the throttle in a lower gear. With the added torque of the supercharger, it was now very easy to steer with the throttle during a test drive on the site of the 1996 Palm Springs Vintage Grand Prix, something that was not possible with these wheels and tires prior to the installation of the supercharger.

Even more noticeably, in everyday driving, the torque is there regardless of gear or engine speed. Push down and it goes, or, if you are so inclined, kick the fire and light those tires. Alex Zenardi would feel right at home in a supercharged Boxster, it's that much fun.