Prepared and submitted to Excellence® Magazine for the June 2009 Issue:


Turbo Boxster
By Zachary Mayne

There aren’t too many obvious clues that tip off the performance that’s available from the subtle looking Guards Red Boxster S that we’ve come to Phoenix, Arizona to drive. In fact, unless you’re seated in the driver’s seat, there are really only two things that might let you know that all is not stock under the unassuming exterior. The first one is when the electric wing is deployed and reveals “TurboKraft” lettering across the rear facing side that is hidden when the wing is not operational, but that when in the raised position now gives a hint of the Porsche’s abilities. And of course the other tip off would come when the 986 suddenly disappears down the road with a deep rumble from the exhaust and the ripping, whooshing sound that can only come from a turbocharged, Porsche flat-6.

Luckily for us, we’re not just here to appreciate the Boxster as viewers but to experience it from the driver’s seat as well. Ten minutes after we arrive at TurboKraft’s Mesa, Arizona headquarters, TurboKraft owner Chris Carroll tosses us the keys. As if enjoying the 80-degree Phoenix weather in the midst of winter wasn’t enough, we now have a drop top, mid-engined, turbocharged Porsche at our disposal. Life could certainly be worse.

“Two years ago, I realized that the Boxster was going to be the next 944,” says Chris, a friendly and youthful-looking Arizona resident who was raised in Berlin, Germany. It’s easy to see his point. Like the 944, the Boxster has been a huge commercial success, so there are a lot of them available second hand for a reasonable price. However, like the normally aspirated iterations of the 944, the Boxster has been much lauded for its handling prowess, but criticized from some quarters for a relative dearth of power. “It’s an awesome handling car, but it’s down on power,” surmises Chris.

With the goal of building a faster Boxster, Chris, along with Marc Reviel of TurboWerx in Cedar Park, Texas, set about the task of engineering a forced induction kit for the mid-engine sportscar. TurboWerx handled much of the heavy lifting when it came to the engineering aspect and provided Chris a complete turbo kit. “The goal was to have more power than a naturally aspirated 3.4-liter 996- at a much lower cost than a motor swap,” says Chris. After studying the various turbochargers available, the two companies settled on a Garrett T3/T4 hybrid turbocharger, which they feel is optimal for applications where low-boost pressure but high efficiency are part of the game plan. As an example, this unit is often used on high-power four-cylinder applications. And since the plan was to engineer the kit to use the stock Boxster’s 11:1 compression ratio, they couldn’t get too crazy with the boost pressure.

“We wanted to design the kit to be put in a box and shipped,” says Chris. The idea being that someone with decent mechanical skills could install the kit in a weekend or so. The kits themselves are packaged at TurboWerx’s headquarters in Texas. “Each kit is 100-percent complete where the installer need provide nothing but lifting the car up and the tools to install,” says Reviel. “We even provide a ninety page full color manual to make the process easy enough for the owner to do themselves.” Alternatively, they could simply hand over said box of power to their Porsche mechanic of choice and pick up a much faster Boxster a couple of days later. According to Chris, the most difficult aspect of the conversion is replacing the fuel injectors, since they are so challenging to get to thanks to the Boxster’s cramped engine bay.

The kit utilizes a stainless steel turbo downpipe, while all other necessary plumbing is also stainless steel, including the Y-pipe that goes from the turbos to both of the headers. On the exhaust side of the equation is a Borla stainless steel muffler that exits of out of dual tips. Chris is cagey when asked what the exact diameter of the Borla muffler is, only revealing that the company experimented with three different sizes before ending up with the one they’re using. A Tial wastegate is also installed, inside of which is the spring that controls the turbo’s boost. The standard spring offers 6 psi of boost, which equates to a little less than one half bar. There is also a custom tube that routes from the Boxster’s stock mass air flow sensor (MAF) to the turbo.

In order to supply an adequate amount of fuel to the motor, the kit includes Siemens fuel injectors that are 25-percent larger than the stock injectors. The turbo conversion also requires that the Boxster’s ECU be sent out to have revised fuel and timing curves programmed into it. According to Chris, special care was taken in the design of the conversion to allow the car to run on California’s 91-octane pump gas.

On the passenger side of the engine bay is an aluminum air-to-air intercooler, ensuring that the turbo gets a steady supply of cool air. “The engineers spent a lot of time working on air flow to the intercooler,” says Chris. “We also experimented with an air-to-water intercooler, but it wasn’t as effective as the air-to-air setup.” The turbo’s oil supply comes from the motor’s oil and is circulated through a braided steel line fed by a custom designed electric scavenge pump mounted on the gearbox. The mounting location ensures that the pump remains completely silent while it’s in use.

The Guards Red Boxster S that TurboKraft made available for our driving impressions was one of the first Boxster S customer delivered cars and is owned by the son and father duo of Dennis Wilson and Douglas Wilson of Globe, Arizona. Shortly after acquiring the second hand Boxster, Dennis approached TurboKraft about getting more power out of it. “We talked about reflashing the ECU, installing an intake and an exhaust, basically all of the bolt-on stuff,” explains Chris. By the time it was all added up, according to Chris the cost of the parts and installation was more than just the cost of turbocharging the Boxster. It didn’t take much more convincing before Dennis decided to go the route of forced induction.

Before the turbo was installed, the stock motor was tested on a Dynapack chassis dyno. It produced 213.5 rear-wheel horsepower at 6,240 rpm and 206.8 lb/ft of torque at 4,671-rpm. Figuring a 15-percent loss for parasitic driveline loss, those numbers are right in line with the factory’s claim of 252 flywheel horsepower for a stock 2000 Boxster S. With the turbo installed, the Boxster’s engine was tested again. This time it pumped out 300.6 horsepower to the wheels at 5,600 rpm and (more importantly) 304.4 lb/ft of twist at 4,519 rpm. According to the dyno, the TurboKraft Boxster was putting out nearly a hundred more flywheel horsepower than a stock S. The final numbers are definitely enough to meet the project’s directive of eclipsing the 300-hp 3.4-liter produced by a naturally aspirated 996’s flat-6.

In order to get a better feel for how the turbo conversion changes the character of the Boxster S, we arranged a stock example as well for back to back driving impressions. Granted, the Seal Grey version provided by readers Jerry and Jan Mackulack is a slight step beyond a 2000 model, but the differences are not that drastic. Minor changes to the VarioCam variable valve timing as well as the then most current Motronic ME 7.8 software means that an ’03 S puts out 258 horsepower, around six more than a stock 2000 S has. The pristine condition of this example, the stunning color and the fact that its riding on 18-inch Carrera wheels makes it the picture of perfection. “We’ve owned it since 2003, when Jerry bought it new for himself,” Jan tells us. “It was passed down to me a few years ago.” The Seal Grey S is actually the fourth Boxster that the Mackulacks have owned, in addition to a few 944s (normally aspirated and turbocharged) and 911s. But it’s the Boxster that seems to be the biggest hit with them. “I love the car since it is so balanced,” says Jan. “Its great on an autocross course and the freeway. It really handles much better than any of the other Porsche we have owned… and its sexy.”

We grab the keys to the stock example first for some quick driving impressions. The flat-6 lights up with a throaty burble and the 6-speed snicks easily into first. Considering the shape that this one is in, it feels like 2003 all over again. Once on the move, the revised 3.2-liter offers decent acceleration in the mid-range, but to really get things moving the motor needs to be planted in its sweet spot between 4,000-rpm and the 7,200-rpm redline. Keep the engine singing here and there’s plenty of power, the Boxster bounding forward with a happy, ripping canvas wail. It’s a vivid reminder of how right Porsche got the sound of the original S, a terrific combination of throaty exhaust notes overlaid at higher rpms by the intake snort thanks to the location of air intakes just aft of the cockpit. On the shifting side of things, the 6-speed offers quick, smooth throws for up and downshifts.

It’s when we guide the Boxster through a series of high speed sweepers though that its forte is revealed. This Porsche remains one of the most eminently chuckable sportscars around. Handling is flat and very neutral. Push hard and the nose runs just every so slightly wide, but its never too much that some inputs through the steering, throttle or brakes can bring it back to a neutral stance. Its addictive stuff, and we quickly find ourselves ripping out of turns and snicking the gear lever up through the gears.

Pulling to a stop next to the waiting Guards Red S, about the only complaint I can level at the ’03 version is the fact that the chassis so outclasses the power output. The 3.2-liter is an incredibly sweet motor, with tons of character, but the accomplished chassis feels under-utilized.

Question is, will strapping a turbo to the motor maximize the potential of the brilliant Boxster? To find out, we climb into the TurboKraft Boxster. Once ensconced in its tan leather interior, there’s little to give the forced induction game away. With the exception of the Autometer boost and exhaust temperature gauges mounted on the center console, the interior remains identical to how it left the factory. A twist of the ignition awakens the flat-6, which fires with a deep burble through the Borla muffler that is far more aggressive sounding than the stock version. The clutch remains light and easy to modulate as we pull away from a stop, though unfortunately the same cannot be said of the B&M short shift kit that this one is equipped with. A great idea in theory, for some reason this one is very heavy, forcing us to really muscle it through the gears. Possibly it is need of something as simple as an adjustment, but there’s no getting around the fact that as it is, it’s heft gets in the way of rapid progress.

Speaking of rapid progress, the red Boxster is indeed now quite rapid. From as soon as 2,000 rpm things start happening far quicker than in the stock S. Boost builds quickly beyond that point, rocketing the Porsche forward in a manner that feels very similar to what you experience in a stock 996 Turbo. In fact, to be honest, the acceleration feels even stronger than expected. Along the way, the turbo whooshes and the exhaust wails a guttural flat-6 song. In the higher reaches, it lacks the crisp sound of the stock S, a byproduct of the turbo and the louder Borla muffler, but for devotees of forced induction Porsche sounds, the tradeoff is more than worth it. Though the Borla is relatively quiet at lower rpms, once the mid-range is broached, things get considerably louder. For those who want a quieter sound track though, TurboKraft can also install a mellower muffler that Chris says is about five decibels quieter while only robbing a couple of horsepower.

Since Wilson decided to leave the suspension stock, at least for the time being, the Boxster is not quite as adept at going around corners as it is at eating up straights. Thanks to the abundance of power, care needs to be taken as we clip apexes and exit turns. It’s not uncontrollable or scary by any means, just not as buttoned down as it could be. The same theory applies to the brakes. Since you’re needing to shed speed sooner than in a stock Boxster, a little more stopping power is in order. Chris agrees that to get the most out of the Turbo conversion, the car really should be equipped with a stiffer suspension. A set of Bilstein PSS9s and a proper lowering and corner balancing would do this Porsche a lot of good. It should also be noted that this example still has its stock 17x7 and 17x8.5-inch rims, rendering the contact patch minimal at best.

Jerry Mackulack returns from a test drive of the Boxster turbo impressed by the power but not convinced it’s the final word in Boxster tuning. “There are a lot of car people who really enjoy the experience of feeling a turbo kick in and receiving a violent push back in the seat, but unfortunately I’m not one of them,” he admits. “My 944 Turbo S was like this and was not my favorite car for that exact reason. I like the power to be seamless from low rpm to high rpm.” It’s not a criticism of the engineering of this particular turbo Boxster, but rather the sudden power surge that is inherent to turbocharged motors, particularly when there is only one turbo at work. Of course, Jerry admits that the lightswitch power delivery that he dislikes is exactly what some enthusiasts desire.

Ultimately, despite this particular example’s shortcomings in the handling department, this is a great conversion that unlocks the beast hidden inside the Boxster. The combination of mid-engine alertness and a big hit of turbo acceleration transforms this drop-top. So, you’re no doubt wondering how painful this kit is to the pocket book. While not exactly cheap, I’d say that the $8,000 price of entry quoted by Chris delivers strong value. For owners looking for more power out of their Boxster S, this is probably one of the most sure-fire paths. Switching back and forth between the stock S and the TurboKraft example is a vivid illustration of the two car’s characters. After experiencing the turbo, the stock S practically feels as though something is wrong with it until you get the revs way up there. Granted, the high-revving, normally aspirated power delivery is one of the appeals of the Boxster. On the other hand, there’s a lot to be said for a slug of easily accessible turbo torque, a trait that defines many of the greatest Porsches.

Perhaps most importantly, this conversion doesn’t feel as though it’s stretching the Boxster platform to the limits of its horsepower capacity. As Chris says, “There are no special tricks to driving it, it’s as easy to drive as a stock Boxster- no super lightweight flywheel, no twitchy throttle, just get in and drive.” In this case, the relatively modest power output is a perfect compliment to the chassis… just don’t forget about that suspension upgrade.