A Wolf in Wolf’s Clothing

A flamethrowing 993 GT2-bodied 930 racer

Wolf in Wolf’s Clothing 930 1
September 11, 2014

Few club level race cars can tout international competition credentials and fewer still as extensive as Urs Gretener’s 993 GT2-bodied 1983 Porsche 930. Though this racer now calls the storied Laguna Seca its home track, it first competed at Imola, Monza, Dijon, Hockenheim and the Nurburgring.

“We called them flamethrowers!” Gretener said, remembering the first time he watched turbocharged 911s take to the Circuit de Dijon-Prenois in France.

“Flames would pop from the tail pipe at the end of the straight,” he said with a grin. Throughout the 1980s, the Swiss-born, highly energetic Gretener raced a 1980 911 SC throughout Europe.

In 1990, Urs moved to the U.S. to start his own fabrication business, Gretener Prototype Engineering, in Paso Robles, California. While much of his time went into his business, he yearned to get back in a racing seat.

“I had left my SC at my parents’ home in Switzerland, so I would only get to fly back a few times a year to run it at Dijon or Hockenheim,” said Gretener. “Then, I sold my ’80 911 and started looking for a 964 RS.”

A 260-hp Carrera 2 RS would have been a nice step up from the 3.0 SC, but Gretener’s long-time friend, fellow Swiss race driver, and owner of the Swiss Garage Hausherr race shop, Markus Hausherr, had other ideas.

“Markus had a white 1980 930 that he ran at the track,” Gretener remembered. “We were at Dijon and he wanted me to go for a ride in his car before I made up my mind about buying a 964. We went out for about three laps, then he pulled into the pits and said, ‘Driver change.’” After a half-dozen laps on the 2.4-mile circuit, Gretener forgot about the RS.

“I had never driven a turbo before, but it felt just right,” Gretener said. “The power, the balance, the whole car was amazing!”

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Shortly after Gretener’s first Turbo drive, one of Markus’s clients blew up his track-prepared 930’s engine and wanted to sell the car.

“It was actually a good opportunity,” Gretener said of the broken-down Turbo. After taking delivery, he decided he didn’t want to swap the expired powerplant for an OE replacement. Instead, he wanted Markus to build a Ruf BTR Gruppe B competition-spec racing engine.

To do this, Markus enlarged the 3.3-liter flat six to 3.4 liters using bigger Mahle pistons and new cylinders. He also installed a performance intake manifold, lumpy 935-type camshafts, a throaty new exhaust system, a Kuhnle, Kopp and Kausch K27 turbo and a large Ruf intercooler.

With the boost level set at 0.8 bar (11.6 psi), the engine made a respectable 374 hp on the dyno. Testing the car, however, would have to wait.

Coming to America

While the 930 had been run extensively on racing circuits across Europe, it was registered in Switzerland as street vehicle. Under strict Swiss vehicle codes, the new engine made the 930 illegal to drive on public roadways. However, that was of little concern to Gretener, who had other plans for his new ride.

“I brought it into the U.S. knowing

it was only going to be raced,” said Gretener. The previous owner had installed a Heico aluminum roll cage and stripped out the interior, so the Turbo had already been on its way to becoming a dedicated racer.

Wolf in Wolf’s Clothing 930 3

Although its torsion bars were stock, they were fitted with Delrin polymer bushings. The 930 also came with a custom strut tower brace and stiffer RS shock absorbers. At the corners, the stock brakes were still in place, but they were enhanced by a unique cooling system.

“There were little brass nozzles mounted on the struts that sprayed water into the front rotors,” Gretener said. “It was for cooling the brakes at the Nürburgring.”

Purpose Built

The car had hardly been on American soil for a week when Gretener and a friend rolled it into his shop and began tearing it down.

“We started on Thanksgiving weekend and had it stripped down to the bare chassis by Monday,” he remembered.

Gretener removed the aluminum cage in favor of a 14-point NASCAR-style cage that tied the suspension points to the chassis.

“We basically created a semi-tubular chassis car,” Gretener said. At both ends of the car, the torsion bar suspension system was replaced with 935-style ERP coil overs and Bilstein RSR shocks and struts.

The traditional spring rates for air-cooled 911s are 400 lbs in front and 600 lbs out back. However, Marcus’ experience revealed higher rates would give the car far better handling on the race track.

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“We started with 850 lbs up front and 1,150 lbs in the rear,” Gretener said. To fine-tune the new suspension, a new tubular anti-roll bar was installed up front and a 22mm solid bar was installed out back.

To reign in the power of the Ruf-spec motor, Gretener continued to rely on the 930’s original brake package, as the 917-derived discs and calipers were, at the time, the largest ones fitted to a production Porsche.

Gretener assembled the car with IROC-style bodywork from Getty Design of Santa Ana, California. Along with the massive front spoiler and enlarged fenders, the kit included fiberglass doors and a 3.8 RSR rear deck lid with a 50-inch wing. To finish it off, the newly refreshed 930 got three-piece BBS wheels wrapped in Yokohama slicks—240/640/18 up front and 280/640/18 in back.

A New Home

While Willow Springs International Raceway, near Rosamond, California, can hardly be considered as historic as Imola or Hockenheim, it is a formidable circuit for the unacquainted driver.

Willow was the Southern California Porsche Owners Club’s home track when Gretener originally joined. Thus, it became the American testing ground for the revamped 930.

“It was already a dinosaur,” Gretener said, as most top P.O.C. racers in the late 1990s were fielding 964 RSs or modified 993s. Draped in the bodywork of an IROC racer, the then-silver and black 930 looked dated. But as with all things on track, the stopwatch made the final judgment.

The Turbo proved to be quick, clocking consistent 1 minute 30 second lap times. Given its improvements and preparation, the scrutineers placed Gretener’s 930 in the R2R racing group. Over the following seasons, Gretener became one the club’s most avid and successful racers, but he had yet to tackle one challenge.

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“I really wanted to run the Tribute to Le Mans,” the Swiss said of the P.O.C.’s springtime four-hour day-into-night endurance race at Willow Springs.

By the 2001 running of the Tribute, Gretener had enhanced the 930’s performance further. He widened its fender arches and filled them with larger 250/650/18 and 290/680/18 Yokohoma rubber, front and rear, stretched the rear wing to 60-inches and fabricated a smooth three-piece aluminum belly tray.

“The undertray was a huge improvement,” Gretener said. “It gave the car better top-end speed on the front straight. We immediately started seeing times in the 1 minute 24 second range!” This placed Gretener and Markus, who was co-driving, near the front of the enduro’s starting grid.

The pair maintained a winning pace in the early stages of the race. However, when the checkered flag fell, the Swiss duo found themselves one lap behind the winners.

“It was still an amazing race and it felt good to run that strong,” said Urs. While Gretener was disappointed not to score the win, he proved his much older Turbo could give the newer racers a run for their money.

More Speed

Not long after the Tribute race, Gretener had the opportunity to do some hot laps in Martin Snow’s ex-Rohr 993 GT2 racer. It was the beginning of the 930’s most drastic transformation.

“That’s when I got a taste of real speed,” Gretener said of the 3.8-liter, twin-turbocharged factory racer. “I knew that was the direction I wanted to go with my car.”

Wolf in Wolf’s Clothing 930 6

Gretener stripped his 930 down to a bare shell again. This time, it would get a full 993 GT2 body and an even bigger engine.

In order to accommodate the new GT2-style front bumper and air ducting, Gretener had to make a few alterations to the 930’s tub. After that, fitting the competition-inspired EVO II body kit from Getty Design was a straightforward affair. In addition to looking fresher, the new body also allowed Urs to incorporate ground effect aerodynamics into the car.

“The undertray is made from a sheet of honeycombed carbon-Kevlar from a C-17 military plane,” Gretener said. “The added downforce really helps the car’s handling through the high-speed turns.”

While the 3.4-liter BTR powerplant had proven itself plenty capable, Urs wanted the same level of thrust he experienced in the GT2. For that kind of power, the Swiss went to Porsche AG.

“It’s a 3.6-liter Turbo S motor,” Gretener said of the twin-turbo flat six that now rests between his car’s broad haunches. Although the engine was complete when it arrived at his shop, Gretener made a few changes to Stuttgart’s workhorse.

“We installed a Motec ignition system, bigger fuel injectors and a larger intercooler,” he said. These changes, combined with 1.0 bar (14.5 psi) of boost, increased the engine’s original output of 438 hp to an impressive 537 hp at the flywheel.

“We set up the car so that it doesn’t have adjustable boost. That’s what gave turbo motors a bad name,” explained Gretener. “A lot of guys try to run them with the boost cranked way up and the motor just can’t hold together. It’ll last 100 hours at 1.0 bar of boost, if not more.” He also noted that a lot of the factory GT2s had a boost adjustment knob, but it was usually located out of the driver’s reach.

Surprisingly, Gretener decided to retain the 930’s original four-speed 930/30 transmission. However, he did rebuild the gearbox with cogs tailored to the new engine’s power band.

Wolf in Wolf’s Clothing 930 7

“Because the new motor has so much torque, I don’t need a five-speed box. With the higher ratios, I basically have four usable gears.”

Knowing the suspension would be working harder under the more aerodynamic body, Gretener increased the spring rates to 1,450 lbs and 1,850 lbs, front and rear. The most substantial improvement to the car’s handling came from the installation of the adjustable JRZ shocks. “I think the JRZs alone made us 1.5 seconds quicker,” Gretener estimated.

To scrub off that speed, Gretener equipped the 930 with massive Brembo 355mm floating cross-drilled rotors paired with four-piston aluminum calipers and Pagid racing pads.

Topping the brakes are 18×11 and 18×13 three-piece BBS aluminum wheels wrapped in big 280/650/18 and 330/710/18 Yokohama slicks, front and rear.

Back on Track

When Gretener rolled out the 930 in its latest guise, it had come a long way from its days of challenging the Nürburgring in the ’80s.

“Right away we were in the low-1:20s at Willow Springs!” Gretener said. “We had a few issues with the boost at first, but that was about it. My goal was to get into the 1:19s.”

That near-record time eluded him throughout the car’s first weekend back racing, but not by much. Urs put the car on pole for its first race, with a 1:20.65 lap time. From that point forward, the GT2-inspired racer rarely missed a podium finish.

As for that evasive lap time at Willow Springs? It took a bit more tuning and a tad more finessing, but during one Saturday afternoon race Gretener managed to push his racer around the circuit to a lap time of 1:19.47. Not bad for a dinosaur.

Also from Issue 223

  • 1,000 Miles in a 991 Turbo S
  • A Brief Golden Age: The 917
  • Market Update: 1974-89 911
  • First drive of the Ruf anniversary drop top
  • Street Fighter 904
  • Profile: Klaus Bischof
  • Four-Cam Speedster
  • Coming Home: Le Mans
  • Explained: Direct Fuel Injection
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