Don't get me wrong--I love the 3.2-liter engine in Porsche's Boxster S. It just needs shorter gearing, given the torque output throughout the midrange. Heck, it's got a first gear as tall as a 2002 996 Turbo with the 450-bhp X50 package. Until 2004, Porsche continued to stuff the same year's naturally-aspirated 996 gear and final drive ratios into a car with a nearly 20 percent less favorable power-to-weight ratio.
Imagine Auto of Lenexa, Kansas, a company that specializes in the servicing and build-ups of Porsche 911s and Boxsters, has a solution--in the form of two boosted Boxsters.
The red 1997 2.5-liter Boxster doesn't appear any different from stock; no aesthetic upgrades except for a set of 18-inch Sport Design wheels. Bigger brakes are unnecessary because the factory Porsche brakes are simply outstanding. The suspension hasn't been touched, keeping the car as street-friendly as the day it rolled off the showroom floor. But its owner decided it was time to ante up the power to Boxster S levels.
After a call to Imagine Auto, his car now sports an IA stage one supercharger system, which uses a C1 Pro Charger centrifugal blower that makes a joke of the stock 201 bhp rating. After establishing a 160 wheel-hp baseline on Imagine Auto's dyno, the blower pushes 231 wheel-hp at just 4.5 psi, surpassing the 250-bhp 986 Boxster S (produced in 2000-02) by 11 wheel-hp (2003 986 S increased to 258 bhp; to 280 bhp in 2005 987 S models; and to 295 bhp in the current 2007 987 S model). Peak horsepower gains over the plain Boxster's stock 2.5-liter are an impressive 74 wheel-hp and 60 lb-ft of torque at 6600 rpm.
IA limits the boost level of the stage one system at 4.5 psi and keeps the ignition timing conservative because there's no intercooler. "This power level was where I felt it was safe for the intake temperatures we were seeing. Both cars actually made more power than we're showing here, but we turned [the tuning] back to stay on the safer side," says Imagine Auto's founder, Steven Kaspar. "95 degrees F on our dyno here is different from, say, when we test cars in the canyons of Texas at the exact same temperature."
IA says it has a run-down Boxster with well over 100,000 miles, which continually gets abused by its owner in the scorching Arizona heat, and that car is still running strong. When asked about an intercooler, IA confirms a liquid-to-air intercooled stage two system is in the works, which will allow the tuning to be more aggressive at the same boost level. Due to low demand, IA does not plan to produce a supercharger system for the newer 2.7-liter Boxster engines.
Although the car is definitely quick, I was most impressed by the incredible smoothness of the power delivery. Acceleration feels like that of a 986 Boxster S, only with a better top end. On the dyno graph you'll notice the slight advantage a stock Boxster S has in the low end and middle of the range, but this car's shorter gearing makes up for it.
The slow-rising, incremental boost of a centrifugal supercharger gives a slightly upward-sloping torque curve nearly all the way through to the redline, making the car feel like it wants to pull harder and harder. Forget feel, it does pull harder as the engine revs climb, with no sign of giving up. Compared to a stock 986 Boxster, there really is no compromise in power here--it's faster the second you step on the throttle and the gap gets bigger and bigger as the revs increase. And interestingly enough, this test was done with the stock exhaust system.
The black 2000 Boxster S looks more aggressive. It sports a factory wing and aerokit, has been lowered with H&R springs, and rides on 18-inch 993 Turbo-style wheels. From the rear, the only performance upgrade hint is the dual-tip Cargraphic muffler. The mods are subtle, but they make for one of the finest 986 Boxsters you'll ever see.
Fire the car up and the whine of a blower hits the ears. This Boxster S is powered by the same means as the red car, although the actual plumbing is a little different to accommodate the larger motor. Additionally, the supercharger kit--which is available for all 2000-06 Boxster S models--includes a different throttle body assembly, a pair of newly fabricated headers and larger fuel injectors.
With the IA stage one kit, it idles like stock and--since it retains the factory clutch--feels exactly like stock when cruising around town. Lay into the throttle, however, and all bets are off. This car just goes and goes. Like the stock car, 4500-6500 rpm is where there's the most dash for the cash. The torque curve doesn't change in shape after 2700 rpm, but with the 3.2-liter motor now juiced by an extra 4.5 psi, the pull is much more intoxicating. It feels as if the motor increases by a half-liter of displacement with each 1000-rpm increment. Superb.
The stage one non-intercooled set-up is enough to spin IA's dyno to 282 wheel-hp-62 wheel-hp over stock-and a 50 lb-ft average gain in torque from 6000 rpm through to the redline. With power to the wheels now surpassing that of a 2004 320-bhp 3.6-liter Porsche 996 (a stock example scored 257 wheel-hp on IA's dyno), this Boxster S commands respect. And now I think that factory Boxster S gearing works perfectly.
2000 PORSCHE BOXSTER S
Longitudinal mid-engine, rear-wheel drive
3.2-liter flat six, dohc,four valves per cylinder, supercharged
F: Four-piston monoblock calipers, 12.5-in. cross-drilled rotors
R: Four-piston monoblock calipers, 11.8 cross-drilled rotors
Wheels and Tires
993 Turbo-style 18-in., Toyo FZ4 235/40 (f), 265/35 (r)
Power: 282 hp @ 6550 rpm
Torque: 241 lb-ft @ 5750 rpm
*measured at the wheels, Mustang
1997 PORSCHE BOXSTER
Longitudinal mid-engine, rear-wheel drive
2.5-liter flat six, dohc, four valves per cylinder, supercharged
F: Four-piston monoblock calipers, 11.7-in. vented rotors
R: Four-piston monoblock calipers, 11.5-in. vented rotors
Wheels and Tires
Sport Design 18-in., Pirelli P-Zero, 235/40 (f), 255/35 (r)
Power: 231 hp @ 6700 rpm
Torque: 186 lb-ft @ 6200 rpm
*measured at the wheels, Mustang MD dyno