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Porsche 956/962 engines – Group C vs IMSA
Published: 26th July 2019 By: Martin Raffauf
Online version: https://www.porscheroadandrace.com/porsche-956-962-engines-group-c-vs-imsa/
Lined up for the photo shoot following scrutineering for the 1982 Le Mans 24 Hours are the three works Group C Porsche 956s – they would finish the race in the order of their racing numbers: the #1 finished first, the #2 was second and the #3 third
In the early 1980’s there was a divergence in the rules for sports car racing world-wide. IMSA (International Motor Sports Association) in the USA proceeded with the GTP concept. The GTP (Grand Touring Prototype) was a prototype car using street car based engines. By 1982, the FIA was moving to a fuel based formula for sports cars. Porsche knew the 935 was no longer competitive and so they developed the 956 Group C car. It was highly successful, www.porscheroadandrace.com
finishing 1-2-3 at its second race, the 1982 Le Mans. It was a ground effects prototype car with an engine type of 935/76. A flat six-cylinder, which was based on the earlier 936-engine (which in turn used the still-born Indianapolis race car engine). It featured a combination of water-cooled cylinder heads and air-cooled cylinders. The engine specifications were as follows:
Type 935/76 (1982)
Displacement 2.65 litre (2649 cc)
Horsepower 620 bhp @ 8200 rpm; 1.2 bar boost (standard boost)
Torque 630 Nm
Turbochargers Twin turbo KKK K26
Cooling Water-cooled cylinder heads, air-cooled cylinders with fan
Fuel feed Kugelfischer mechanical injection www.porscheroadandrace.com
Exploded view 1982 Porsche 956 (© Porsche Werkfoto) www.porscheroadandrace.com
Rothmans 956 with engine type 935/76 at Le Mans in 1982 www.porscheroadandrace.com
Turbo and exhaust installation on factory 956 in 1982. KKK K26 turbos were used
The factory ran these cars in Rothmans colours in 1982 but they only sold customer versions of the 956 in 1983. IMSA refused to allow the 956 in the Camel GT series as it did not meet the rules in several areas: (1) It was deemed to be unsafe with the driver’s feet in front of the front axle. For safety reasons, IMSA GTP (Grand Touring Prototype) rules specified the driver’s feet had to be behind the front axle centre line; (2) The 956 also used a ‘non- production’ based engine, which was not IMSA legal; (3) The 956 had an aluminium roll cage which IMSA was not happy with, and in fact banned completely in 1983; and (4) The 956 only had a 100-litre fuel tank, whereas IMSA GTP regulations called for 120 litres. www.porscheroadandrace.com
As Group C progressed, fuel management and engine economy became more important. The FIA limited the amount of fuel a car could use during a race, so fuel management became critical. In 1983, this engine (935/76) was improved by moving from mechanical to electronic fuel injection. It was designated 935/79 and it used Bosch Motronic 1.2 engine management. The interesting thing was, the factory Rothmans cars ran this engine in 1983, but the customer cars were sold with the 935/76 engine. The displacement could be altered on this engine with bore and stroke changes to 2.8-litre, 3.0-litre and 3.2-litre. Because of fuel restrictions in the races, in the early days, only the 2.8-litre engine was utilised for races. However, Brun and others did build some larger 3.2-litre qualifying engines in later years. In the early years, the factory was always one step ahead of the customer cars. Ostensibly, they were testing the new developments prior to selling them, and the switch from mechanical to electronic injection was a big improvement, but required a lot of testing, and provided some early issues that had to be overcome.
Type 935/79 (1983 – 1986)
Displacement 2.65-litre (subsequently 2869 cc, 2994 cc and 3164 cc)
Horsepower 620 bhp @ 8200 rpm; 1.2 bar boost (2.649-litre)
Torque 630 Nm
Turbochargers Twin turbo KKK K26 www.porscheroadandrace.com
Cooling Water-cooled cylinder heads, air-cooled cylinders with fan
ECU Bosch 1.2 Motronic engine management
While the FIA was running sports car racing on a fuel limit basis (i.e. a given amount of fuel was allowed per race distance), IMSA in the USA went completely in the opposite direction. They had championed the introduction of IMSA GTP cars which had no fuel restrictions, other than a maximum on board capacity of 120 litres (Group C was 100 litres). The first approved Porsche GTP car was the March of Gianpiero Moretti. He approached ANDIAL in 1982 to install a Porsche engine in a March 83G chassis. Initial fitting work involved a bell housing and some cooling improvements for the engine bay. ANDIAL, along with help from Porsche Weissach and March Cars (Porsche-March), built this car in late 1982.
The 1983 Porsche March of Al Holbert which subsequently won the Daytona 24 in 1984 sits at Porsche Rennsport 2018 next to a 956 of John Fitzpatrick Racing www.porscheroadandrace.com
ANDIAL was the Porsche repair and service company started in the early 1970s in Southern California by Arnold Wagner (AN); Dieter Inzenhofer (DI), and Alwin Springer (AL). They originally looked at using the two characters of their first names, but decided to go with AN for Arnold, as ANDIAL sounded better. They had a lot of experience in the late 1970s building and developing 935 engines, and in fact built a whole car, the ANDIAL 935-L, which won the Daytona 24 Hour race in 1983.
In 1983 ANDIAL also built all the engines for Al Holbert’s Porsche-March 83G, Adrian Newey’s first March car (the earlier 82G was not a Newey designed car), which won the IMSA championship. This early GTP March engine was very similar to the late 935-engine using a single turbo and Kugelfischer mechanical injection. www.porscheroadandrace.com
The Porsche-March 83G used by Al Holbert to win the IMSA championship in 1983. A lot of the early, eventual 962 engine development was done by Andial and Weissach on this car. It also won the 1984 Daytona 24 Hours with the Kreepy Krauly team
For 1984 Porsche finally decided to build an IMSA legal car with a slightly longer wheelbase, which resulted in the driver’s feet being behind the front axle. This car was the type 962, and it raced for the first time at Daytona in 1984. Although Mario and Michael Andretti put it on the pole, it failed to finish due to engine and gearbox issues. The Porsche- March, now under the auspices of the Kreepy-Krauly team won the race, running the ANDIAL single turbo engine with mechanical injection that Holbert had used in 1983. www.porscheroadandrace.com
Daytona 24 Hours, 4-5 February 1984: The #1 Porsche 962 driven by Mario and Michael Andretti was powered by a 2869 cc boxer engine developing 650 bhp and fitted with a K36 turbocharger. The car retired after 127 laps with a failed gearbox
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1984 Porsche 962-IMSA schematic – engine type 962/70 (© Porsche Werkfoto) www.porscheroadandrace.com
Porsche 962-001, the first 962 ran at Daytona in 1984 and was then put in the Museum
Along with the chassis regulations, IMSA decreed that only ‘production car-based engines’ could be used. Therefore, the IMSA 962 could not use the Group C water-cooled heads, as there were no street cars sold at the time with such an engine. The single turbo, single spark plug per cylinder, air-cooled engine based on the 930 street turbo could be used (in effect the same engine as the 934). Porsche put the 2.8-litre 962/70 engine in the car in 1984, so all 1984 IMSA 962 cars were sold with this engine. Specifications as follows:
Type 962/70 (1984) www.porscheroadandrace.com
Displacement 2.8-litre (2869 cc)
Horsepower 680 bhp @ 8200 rpm
Torque 660 Nm
Turbocharger Single turbo KKK K36
Cooling Air-cooled cylinder heads and cylinders with fan
ECU Bosch Motronic 1.2 engine management www.porscheroadandrace.com
Porsche 962/70 engine schematic showing the exhaust, turbo and intercooler layout of the original factory cars sold in 1984 (© Porsche www.porscheroadandrace.com
Werkfoto) www.porscheroadandrace.com
1984 IMSA 962 engine layout with exhaust, turbo and waste gates. Original cars came with side mounted intercoolers (© Porsche Werkfoto)
Porsche 962-109, one of the early IMSA cars with a long tail and side intercoolers www.porscheroadandrace.com
Porsche 962-102, a 1984 IMSA car with long tail and side intercoolers and fitted with a 2.8- litre engine (© Martin Raffauf)
In the IMSA series, the 2.8-litre engine quickly proved insufficient for the type of racing in the USA. The IMSA races tended to be shorter, with a lot of sprint races as compared to the Group C races which were longer fuel economy runs. The tracks were much rougher in the USA than in Europe. Group C races were all fuel limited, i.e. you got a specified amount of fuel for a specific race distance, so fuel, mileage and the weight of the car were critical. Probably one of the reasons that the factory originally went with the 2.8-litre engine for the IMSA car, was because they thought it would be more efficient than a larger capacity engine. However, IMSA had no fuel limits per race, the race tracks were different in design (from Europe), and the way the races were run put a premium on torque, not necessarily www.porscheroadandrace.com
horsepower. A lot of the modification and improvement, especially on the IMSA engine models was done by ANDIAL in Southern California.
They realised immediately that an increase in engine volume was needed and moved to 3.2- litre engines. ANDIAL, led by Alwin Springer, Dieter Inzenhofer and Arnold Wagner did much of the development work in close cooperation with Al Holbert and his Lowenbrau team. Jim Busby Racing, who were also based close to ANDIAL in Southern California, also assisted in various ways. ANDIAL modified the Motronic EPROM (engine management system electronics) which proved essential when changing the engine size. Some engine internals and auxiliary components like intake systems and turbos were also modified. After an early period, IMSA relented and allowed twin plug heads as well.
Several major changes were implemented in the IMSA 962 cars, to improve on the original factory delivered car:
The aforementioned engine increase in displacement from 2.8 > 3.2-litre Installation of a top mounted, larger, intercooler, instead of the side mounted factory units. This improved throttle response and drivability by shortening the length of air travel from turbo to engine. This necessitated a slight change in bodywork, as a large air intake was needed on top of the rear engine deck lid. www.porscheroadandrace.com
Jim Busby BFG 962 from the 1985-86 timeframe. Note large top mounted intercooler with re-routed exhaust and turbo placement
Changing to Garrett turbos instead of factory KKK units. Garrett turbos were a major improvement over the standard factory KKK units. Garrett, who were also located in Southern California, cooperated on dyno testing and produced special compressor wheels, which maintained a better turbo efficiency to that of the KKK. This then allowed the option to change the specifications of the hot and cold side housings (snails). Depending on the combinations used, throttle response and/or horsepower could be adjusted to suit a specific circuit. i.e. at Daytona, for example, you might change the turbo configuration to give more top power and sacrifice response, whereas, at a circuit like Mid-Ohio, you might do the exact opposite. www.porscheroadandrace.com
BFG 962 circa 1985-86 design with 3.2-litre engine, top intercooler
Moving the intercooler required a new exhaust system, as the location of all the piping was completely different. A lot of these exhaust systems were made of Inconel by Reid Washbone, again in Southern California. Standard Mahle pistons, and factory crankshafts were kept, but Titanium rods made by Carillo were used, as revs were increased to about 7500 rpm. Although Titanium valves were experimented with, they were deemed unnecessary as the air-cooled nature of the engine limited the maximum revs due to heat. As a result, Titanium valves were not really needed. As Jim Busby put it, “Well, it was the old American, Southern California hot rod thing all over.” A repeat of the hot rod culture of the 1950s and 1960s in Southern California, where small groups and teams made many incremental improvements.
Type 962/71 (1985-1987) IMSA engine www.porscheroadandrace.com
Displacement 3.2-litre (3164 cc)
Horsepower 720 bhp @ 7300 rpm
Torque 720 Nm
Turbocharger Single Turbo – KKK K36 or Garrett ANDIAL
Cooling Air-cooled cylinder heads and cylinders with fan
ECU Bosch Motronic 1.2 management www.porscheroadandrace.com
3.2-litre IMSA engine with twin-plug awaiting dyno work. Top mounted intercooler, air- cooled with fan www.porscheroadandrace.com
3.2-litre twin-plug top intercooler mount IMSA engine in Holbert chassis HR1 www.porscheroadandrace.com
Modified rear tail with scoop to accommodate top intercooler. Walter Brun’s IMSA car design circa 1986 www.porscheroadandrace.com
Holbert HR1 chassis with 3.2-litre with top intercooler as run in 1985-87. Holbert had two cars, this one and 962-103 which had side intercoolers www.porscheroadandrace.com
Bob Akin’s 962-113 in 1986 with 3.2-litre engine and top intercooler (Bill Murrenbeeld – Jerry Woods Collection)
The 962- engine continued to be modified and improved over its life span. The factory stopped building 956 chassis for Group C in 1984, although existing chassis were still ‘grandfathered’ into the Group C championship until 1986. Eventually, after 1984, the factory Group C cars (and customer cars) were all 962 chassis. For 1987, the engines were upgraded to 3.0-litre still using the water-cooled cylinder heads and air-cooled cylinders. More important was the use of Bosch 1.7 Motronic engine management, which was a big improvement over the 1.2 system. The FIA mandated a reduction in fuel octane level for 1987 and this put the pressure especially on the turbo charged engine teams, as the turbo engines were more sensitive to octane than normally aspirated engines such as the Jaguar V12. The factory Rothmans cars used this engine to win Le Mans in 1987, then promptly withdrew from the series. The new engine technology (1.7 Motronic) then trickled down to www.porscheroadandrace.com
the customer teams such as Joest, Brun and Kremer.
Type 935/82 (1987)
Displacement 3.0-litre (2994 cc)
Horsepower 740 bhp (standard boost)
Torque 710 Nm
Turbochargers Twin Turbo KKK K26
Cooling Water-cooled cylinder heads with air-cooled cylinders
ECU Bosch Motronic 1.7 engine management
Continuing reduction of the fuel allotment each year by the FIA resulted in continuing work by the manufacturers on engine management for Group C. Horsepower just for power’s sake became irrelevant and how much power you could make with the fuel allowed, became much more important. Several of the Group C teams would build large qualifying engines at 3.2-litre displacement, qualify, change engines, and then run many seconds a lap slower in the race, frequently on an economy run at the end of a 1000 km race, as they were running out of fuel. Engine type 935/83 was a completely new engine utilising both water-cooled cylinder heads and cylinders. It also made use of Bosch Motronic 1.7 management resulting in about 40 more bhp, and improved fuel economy.
Type 935/83 (1988-1990)
Displacement 3.0-litre (2994 cc) [Restrictors]
Horsepower 740 bhp www.porscheroadandrace.com
Torque 710 Nm
Turbocharger Twin Turbo KKK K26 or ANDIAL Garrett
Cooling Water-cooled cylinder heads and cylinders
ECU Bosch Motronic 1.7 engine management
Slight Improvements were made to the IMSA engine by 1987, which was referred to as the 962/72 engine. IMSA had lowered the displacement allowed for turbo engines to 3.0-litre with restrictors. The updated 962 engine featured increased compression ratio, 3.0-litre displacement and higher RPM limits to 8400. The single turbo was reduced to K32 size, slightly smaller than the K36. This improved driveability and response. However, it still used the Bosch 1.2 Motronic system, and was still completely air-cooled via a fan. The use of restrictors required more EPROM electronics testing by ANDIAL to make the engines run optimally.
Type 962/72 (1987-1992)
Displacement 3.0-litre (2994 cc) [Restrictors]
Horsepower 695 bhp @ 8200 rpm
Torque 710 Nm
Turbocharger Single Turbo – KKK K32 or Garrett
Cooling Air-cooled cylinder heads and cylinders with fan
ECU Bosch Motronic 1.2 management www.porscheroadandrace.com
962-121 at Daytona in 1989. Bayside (as well as Holbert Racing) experimented with this type installation of re-routing the exhaust out through the rear deck as opposed to the back of the car. By this time most IMSA teams, had gone back to side intercoolers as the engines were now restricted and had a 3.0-litre limit www.porscheroadandrace.com
Bob Akin’s final car in 1987, 962-C04 (a Chapman chassis) with side intercoolers
As the end of the decade neared (1980s), the 962 became less and less competitive with the new Jaguar, Nissan, Mercedes and eventually Toyota factory cars in both IMSA and Group C. Engine development continued, to try and keep the now eight-year old chassis design competitive with the newer carbon-based chassis of Nissan, Jaguar, Mercedes and Toyota. Even IMSA now allowed water-cooled engines so that Porsche could compete with the Nissan twin-turbo engines that were making near 1000 bhp by this time. IMSA actually started using restrictors to try and equate the cars, which was the forerunner of BOP (Balance of Performance). www.porscheroadandrace.com
Daytona 24 Hours, 4-5 February 1989: Jim Busby’s single turbo 962 still managed to win the 1989 Daytona 24 hours with the air-cooled engine – the drivers were Bob Wollek, Derek Bell and John Andretti
The last engine made for both the IMSA and Group C 962 was the 3.2-litre type 935/86:
Type 935/86 (1989-1994)
Displacement 3.2-litre (3164 cc) [Restrictors]
Horsepower 740 bhp @ 8200 rpm
Torque 715 Nm www.porscheroadandrace.com
Twin Turbo – KKK K26 or ANDIAL Garrett with electronically Turbocharger controlled waste gates
Cooling Water-cooled cylinder heads and cylinders
ECU Bosch 1.7 Motronic engine management
Bosch 1.7 Motronic dash layout and instruction (© Porsche Werkfoto – Bosch)
Alwin Springer, and ANDIAL, of course took things a little further, by ‘massaging’ this 935/86 engine. Most of his work revolved around the electronics and engine management, although he also used Garrett turbos instead of KKK. By this time in the Group C formula www.porscheroadandrace.com
(World Sports Car Championship & Japanese Group C) fuel economy was critical, as all the major players (Mercedes, Jaguar, Nissan, Toyota and Mazda) spent large sums of money to improve efficiency to meet the newer more stringent FIA fuel limits. www.porscheroadandrace.com
ANDIAL engine Type 935/86 in Japanese Group C, 1991 www.porscheroadandrace.com
In 1991 when Gary Cummings and I were running the Alpha 962 in the Japanese Group C Championship, we started the season using the factory lease engines. By then the 962 was really struggling against the factory Toyota and Nissan entries in Japanese Group C, not so much on outright speed, but on fuel economy. At the first race at Fuji, we were quite slow (in comparison to Nissan and Toyota) on the main straight at around 300 km/h and struggled to finish with the fuel allowed. We would routinely turn the boost down during the race as we came towards the end, and usually ran out of fuel completely on the cool down lap. We changed to an ANDIAL ‘3.2 massaged engine’ for the second event. We did a lot of testing, and Alwin Springer would send us various chips to test, and we would take notes and report back, and in this way improvements were made. I spent a day at ANDIAL with Alwin getting ‘trained’ on 1.7 Motronic. I watched the ANDIAL engine run on the dyno – 885 bhp at higher boost levels, which was quite impressive. The car ran up to 330 km/h at Fuji, the second event, but more importantly, it used LESS fuel. www.porscheroadandrace.com
Turbos in 1991: factory KKK on left, Garrett on right. Garrett’s were superior due to their ‘tune-ability’ www.porscheroadandrace.com
ANDIAL intercooler and turbo installation in 962-168. This is a 3.2-litre Group C engine. Note the exhaust – California made!
However, by then, the chassis was almost ten years old, and not really competitive with the more modern carbon fibre cars. In any case, by 1991, the FIA managed to destroy Group C entirely, instigating the 3.5-litre racing engines. They modified the rules to give the new cars the advantage, and Group C died. By 1994 IMSA had also changed direction completely, opting for the WSC (World Sports Car) concept. These were open top cars, with flat bottoms and either 5.0-litre stock block, or 4.0-litre racing type engines based on street car designs. So, the 962 was relegated to vintage racing except for Le Mans 1994, where a rule loop hole was used to win the race one last time. It was the end of an era in Sports car racing. www.porscheroadandrace.com
Engine installation in the Dauer GT Le Mans 1994, the final 962 iteration. By rule, as a GT car, the exhaust had to exit at the back. This was engine type 935/86
Written by: Martin Raffauf (with Alwin Springer) Images by: Martin Raffauf, Jerry Woods, Dr. Brian Mitchell, Bill Murrenbeeld and Porsche Werkfoto
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