Killer Turbo Porsches: A Driver's Guide

A walk through Weissach's wildest by a guy who's been there

Killer Turbo Porsches: A Driver's Guide
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Feature Article from Hemmings Sports & Exotic Car

September, 2009 - Jim Donnelly

Funny Cars don't just blast through straight-line spurts, not in Europe, although the link between our quarter-mile nitro coupes and their GT cars has been easy for anyone to follow at certain points. A stock production body slithers into something nearly unrecognizable, but still capable of extraterrestrial velocity. What about the driveline? Doesn't matter. If it looks sort of stock, it's legal. That was the coda that created some of Porsche's most mind-boggling interpretations of the competition 911 during a few cockeyed years that began at the midpoint of the 1970s.

It was in those years, after the 917's global reign, that Porsche began to seriously examine the development of the 911 as its platform for international racing dominance. Part of the reason was the 1976 introduction of the 930, an event now marked as a benchmark moment in Stuttgart's racing history, even though the 930 was a street car. The 930's baddest-car-on-the-planet distinction led to creation of the 934, a homologated racer for FIA Group 4 GT death matches. While winged, turbocharged 911 offshoots had existed in the past, this was the board from which Porsche dove into true "silhouette" racing, the world of the road-course Funny Cars.

A wild time, to say the least, and John Starkey both lived it and chronicles it today. A Brit by birth, Starkey is an established technical historian on racing sports cars, having penned 16 books on topics from Lola to the IMSA GTP series. One of his latest, From R to GT2, is a massive work on the race 911s and homologation silhouettes. Unlike most scribes, Starkey lived this era, having raced Carrera RSRs in Europe and a single-turbo 935, plus a Lola T-70.

"I liked the RSR very much. For a start, it was my first "real" race car. Oh, sure, I'd raced an XK120 and an ex-Le Mans Porsche RS 3.0-liter in various hillclimbs in England, but the XK may have had, what, 220hp from a modified 3.8 lump? The RS was quoted at 230, but the RSR had 330, and a lightweight chassis. It went. Not only was it my first taste of real race-car acceleration, it also handled," Starkey recalled. "You could really throw it around. It totally negated all those stories that I'd read for years about Porsches being cars in which the tail shook the dog.

"So I approached the 934 with few qualms, believing that it would be, well, a faster RSR. In that, I was right, but in shoehorning that single turbo engine with its strangled induction system into the tail, Porsche had sacrificed something: driveability. Sure, the 934 accelerated faster than an RSR, but when it came time to get back on the power for the oncoming apex to a corner, after I'd used the brakes, there was no power there to use.

"Sometime around 1994, whilst still living in England, I was lent a 1980 935 K3 for a race at Brands Hatch. After my last experience with a 935, I certainly approached this one gingerly, but wow! What a revelation: instant throttle response, great brakes, RSR handling. I've always liked Brands Hatch, so qualified it third and, in the race, got it up to second before the distributor cap developed a crack and it started misfiring, whereupon I parked it.

"And so to the last 935 I've driven. I'll particularly remember Rennsport 2007 at Daytona for one wonderful, 30-minute period when I got the chance to drive the Vaillant-sponsored green 935 that we have for sale on our website (www.johnstarkeycars.com). I drove it on the banking behind the Interscope 935 with, in front of that, the Joest 935 that won the Daytona 24 Hours in 1980. What a car! I had dug out the dyno sheet from the factory the previous week and glanced at it: 805hp at 7,800 RPM, from a factory dyno. Up onto the banking. Get it all straightened up, press down on the throttle, the turbos spool up with a whine, and, "Oh my gawd!" This is like holding onto a rocket sled, I kid you not. Swiftly grab third and then fourth, watch the revs get to 7,000 and then we're coming down the back straight and catching up to a gaggle of traffic fast. When I got back to the paddock, I switched off, listened to the tinkling sounds of the engine and turbos cooling down and got out, announcing to my friends, 'That's the best race car I've ever driven.'"

"For 1978, Norbert Singer, the development engineer at Weissach, scrutinized the FIA rulebook to see how to make the fastest 935 car permissible. 'Moby Dick,' seen here, was the result. It shocked the rule-makers themselves. Noticing that 'body structure' was defined as only that between the front and rear bulkheads, Singer had his crew cut off every other part of the original structure and used tubing to replace them at the front and rear. The floor was also cut out and a new one was made of fiberglass. The 935 was then lowered by three inches. As Moby's real purpose was to win at Le Mans, where outright speed was key, Singer had the bodywork built with a very long tail and nose. A new rear cowl was fitted above the original rear window.

"The power came from a new, four-valve engine with liquid-cooled heads and air-cooled cylinder barrels. The usual flat fan, used on other 935 engines, was no longer needed, so an almost-standard upright fan was employed. This 935/71 engine produced some 750hp at 8,200 RPM, with up to 800hp available with the boost at 1.7 bar. The gearbox was now mounted upside down to reduce the angles at which the half shafts were forced to work. New brakes, even larger than the Type 917/RSR units, were fitted. When the FIA inspectors came to view the new car, they were aghast. Though they forced Singer to raise the original rear wing so it fit within the car's silhouette, and to remove some of the door skinning, it made little difference. The 935/78 won first time out at the Silverstone Six Hours, but then came a disappointing eight at Le Mans, after developing an oil leak that, upon teardown, proved to have been minor. After two more races, Moby was retired to the Porsche museum.

"As a footnote, two more Mobys were later built by Reinhold Joest. One went to John Fitzpatrick, and the other to Jochen Mass for the Joest team before being sold to Gianpiero Moretti. That car will be seen this year in CER races, driven by Yvan Mahe."

"When the new rules for World Championship races were finally introduced for 1976, Porsche had a new Group 4 weapon to replace the RSR. This was the Group 4 version of the road-going 930, called the 934, seen here in prototype form at the factory. Note the factory spoked wheels, instead of the BBS type that were fitted to the production cars. Porsche faced a big problem with the new 934 since it had to meet its homologated weight, 1,120kg, or 2,464 pounds. As a result, Porsche's racing department even left in the electric windows. The turbocharged single-plug engine of 3 liters' capacity (4.2 liters by the turbo equivalency formula then in use) was unremarkable save for the fact that since Porsche was forced to use the original car's Bosch K-Jetronic fuel injection, it adopted a special, cone-shaped metering unit with greater flow. The engine thus could develop some 485hp, as opposed to the 930's 300. Otherwise, the 934 was in pretty standard Group 4 spec, using 917/RSR-type brakes and torsion bar suspension, very much per the old 1973 RSR.

"That the 934 was fast, there was never any doubt, but its weight was detrimental and most drivers liked the old RSR's handling better. On tight circuits, the RSR, in the right hands, could still beat 934s. For 1977 there was a "934&#8193;" for America and "934/5" in Europe. Both had wider wheels and tires and hence wider, riveted-on fender flares. Both produced up to 650hp by abandoning the K-Jetronic for mechanical injection. The 934 won the European GT and SCCA Trans-Am Championships, but it was not until 1979 that it won its class at Le Mans. This is the 934 prototype, chassis number 930 670 0151, used for factory testing and then sold to Jurgen Kannacher, who turned it into a 934/5 and raced it in the DTM. Afterwards, it found its way to America and has resided over here ever since."

"For 1977, the engineers at Weissach, led by Dipl. Ing. Norbert Singer, developed the 935 with detailed changes to the fiberglass bodywork, including the nose and tail treatment that became standard on Reinhold Joest's 935s in 1979 through 1981. This bodywork was claimed to give 10 percent less drag with the same amount of downforce as the 1976 body shape. The big breakthrough for 1977 was the use of two smaller turbochargers, one per cylinder bank. This made the 935 a lot easier to drive, as it all but eliminated turbo lag. Essentially, that meant the driver had to floor the throttle before the apex of a corner to get horsepower at the right moment. It was a delicate balance. Several drivers taught themselves to left-foot brake to keep the turbo spinning and the revs up. Output was now 630hp at 8,000 RPM and 1.4 bar, with adjustable boost. The designers had taken advantage of new rules that positioned the rear bulkhead 200mm farther forward, allowing more space for the bigger air/water intercooler. There were also new pickup points for the front suspension, and a cockpit-adjustable front anti-roll bar, allowing the driver to make adjustments as the fuel load depleted. The pair of 1977 works-entered cars looked all set for a dominant season until Jurgen Barth wrote one off when his brakes failed at an early race. It took the other car three victories to again win the World Championship in Group 5."

"The Porsche 935 has become an iconic race car, and rightly so. When I asked Brian Redman why he drove 935s, his answer was, "Well, that's all there was if you wanted to win World Championship races at the time!" Of course, he was right. BMW did try to challenge Porsche with a turbocharged CSL in Europe in 1976, but failed and then withdrew from international competition. Their car had prodigious power but simply ate gearboxes. Here, in Martini livery, is the prototype 935, chassis 930 570 0001. Externally, it was very similar to the 1974 RSR Turbo Carrera, the 935 differing mainly in having a two-tier rear wing. Otherwise, you could be excused for thinking that you were looking at a 1974 RSR. Using a 2.8-liter engine, which allowed it to run in the under-4.0 liter class, the 935 weighed just 970kg, some 2,024 pounds. The Group 5 rules allowed more extensive engine modifications than the Group 4, and so the 930/72 engine used in the 935 had twin-plug ignition and mechanical fuel injection, plus an air-to-air intercooler for its single turbo. All told, this allowed the engine to produce around 600hp. In a car as light as the 935, that made for a rocket ship. Suspension was by coil springs, wheels were 11 x 16 diameter at the front and an astonishing 15 x 19 at the rear. The regulations only allowed wheel width at the rear to be 15 inches maximum, so Porsche worked out that a larger diameter than standard, which was 16 inches, would give the tires a bigger footprint.

"The 935 ran afoul of the regulators almost immediately. A loophole allowed the headlamps and their cowls to be deleted, giving the 935 its characteristic droop snoot. The regulators objected, Porsche stuck to its guns and the regulators reluctantly caved. Porsche won the first two races, but then the rule makers objected to the tail, saying that a standard turbo tail had to cover everything. Of course, the new air-to-air intercooler didn't fit, so Weissach was forced to fit a modified 934-type water/air intercooler for the next race at Silverstone, where the clutch burned out and BMW won. At the Nürburgring, there were more modifications to the intercooler system, but the engine failed and BMW won again. It came down to Le Mans, Dijon and Watkins Glen. Porsche won them all against the turbo BMW CSLs."

"As BMW and Ford had retired from World Championship racing by 1977, and therefore left Group 5 effectively to the various race teams that now ran Porsche 935s, the factory saw that the Division 2 section of the very popular German Racing Championship had become a battleground for these makes. Porsche determined to show the world that it could win in whatever class it chose, and so swiftly developed an ultra-lightweight 935, to be known as 'Baby.' It had an engine of just 1.42 liters, which with the turbo equivalency formula made it a 2.0-liter, developing some 370hp. Cars in the 2.0-liter class had to weigh a minimum of just 735kg, or 1,617 pounds. The racing department did the job, but as time was pressing when the car was finally finished, did not have time to test. In its first race, at the Norisring, Jacky Ickx was forced to retire with heat exhaustion. Despite that, Baby appeared soon after at Hockenheim where it left its competitors in the dust. Having proved its point, Baby was retired to the factory's museum."

"Bob Akin was an American privateer who had successfully raced 935s, renting them first of all from Dick Barbour. By 1980, he was racing K3s and for 1981, decided that he would have a 'special' built for his own team's use. To this end, he commissioned Chuck Gaa of GaaCo to build it for him, a car he believed would beat the then-current crop of 935s in IMSA. The resulting car, the 935 LT1, featured a monocoque chassis and the nose section from a Lola T600. Its handling was never sorted out properly, but it was astoundingly fast in a straight line. Modern developments of shock absorbers have since cured the handling problems, and the LT1 is now a very fast vintage/historic racer.

"Like most specials, the LT1 was delivered late and thus encountered, in 1982, the various Lola and March GTP cars then in use. Despite that, it finished in the top 10 of most of the races it contested, until it crashed at Daytona at the end of 1982. It had appeared at Le Mans in June, but retired after running out of fuel after just two hours. Stored for years, it was restored in the early 2000s."

"From 1976 to 1978, the Kremer brothers from Cologne had been developing and racing 935s, using their own ideas. These were called K1 and K2. By 1979, Porsche had finished building 935s, and it was in this year that Kremer Brothers Racing produced its new K3, which went on to being the most successful of all the 935 variants, even winning Le Mans in 1979 driven by Don and Bill Whittington and Rolf Stommelen.

"Although the K3's shape was distinctly different from the factory cars, it was a combination of altering the body/chassis unit, with extra strengthening, plus the use of an air-to-air intercooler, which made the K3 so fast over a long distance. The water-to-air intercooled engines of the factory cars overheated quite quickly under high boost and had to be turned back, with a consequent drop in horsepower, so they would last. The blue car seen here at Le Mans was the actual K3 prototype, which had won the DRM in the hands of Klaus Ludwig. At Le Mans in 1982, John Cooper, Paul Smith and Claude Bourgoignie drove it to eighth overall and the Group 5 win."

"Eckehard Zimmerman of DP Motorsports in Cologne had been the designer and builder of the K3's bodywork for Kremer Brothers Racing, both companies being based in Cologne. After K3 production ceased in early 1981, the Kremer brothers now turning their attention to their CK-5, Zimmerman built a few 935s of his own design, all based upon the standard Porsche-produced 911/930 body shell. This particular 'Vaillant' DP935 was the fastest of all, fitted with an IMSA 962 engine built by the factory's racing department, which produced some 806hp. Willi Rabl used the car to win two European Hillclimb Championships, after Jurgen Opperman had used it to win several races in Germany, mainly around the Nürburgring. Having driven it myself, I can confirm that it was the best handling of all the 934s, 935s and RSRs that I've driven."



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