80's GP Cars

TAG

Porsche turbo engine for McLaren International

THE FORMULA I races of 1984 were an extraordinary run of successes by the Marlboro McLaren team with Alain Prost's domination of the final event of the year, the Portuguese Grand Prix, the team scored an all-time record of 12 wins in a season. With four 1-2 results, in itself a remarkable achievement in such a competitive field, Prost and Niki Lauda amassed 143.5 points in the Constructors Championship, shattering the previous best of 120 points set -by the Williams team in 1980.

Of the 12 wins-the last seven have been an unbroken run-Prost won seven, Lauda five. And from midseason the battle for the Drivers Championship was fought by the two teammates, having left the opposition struggling in their wake. Their battle went right down to the last race in Portugal with the honors going to Lauda by the slimmest possible margin-half a point!

So what is at the center of this enviable tale of champagne and roses? Inevitably our thoughts turn to the heart of the car, the TAG Porsche Turbo engine. But it was not always known by this name; the initials TAG (for Techniques d'Avant Garde) were added some time after the engine was conceived.

When Ron Dennis, designer John Barnard and Creighton Brown bought out Teddy Mayer in their takeover of the McLaren team, renaming it McLaren International they were looking well ahead in the knowledge that turbocharged engines were here to stay. They wanted success above all and, rather than share an engine common to others as a quick entree to the turbo game, as Lotus did, they were prepared to soldier on with the Cosworth-Ford and look elsewhere for a turbo. But there was no established engine available. After careful deliberation they approached Porsche, already well experienced in the turbo field with the Group C racing cars as well as production road cars, a bold move to make as early as August 1981.

But it was a well reasoned move, for Porsche had been eyeing the Formula I scene for some time, and while it did not want to jump in with both feet, its R&D people already had ideas in their heads if not on paper of the type of engine that would fill the bill. The McLaren approach whetted its appetite but with Germanic caution Porsche made it clear it did not wish to undertake the financial responsibility for the project. After many meetings, involving relatively inexpensive areas of discussion, outline drawings of projected ideas and other paperwork, McLaren International took a deep corporate breath, tightened its belt and agreed to underwrite the financing of the design stages.

Work began in November 1981, with John Barnard defining height, width and length dimensions within which the Porsche technicians had to confine their layout. Bear in mind that at the time ground-effect cars were in vogue and one factor Barnard insisted upon was that the lowest part of the engine did not protrude into the "underwing" area so important to his aerodynamic design.

During a 4-month study, the Porsche designers looked at all the options open to them-inline 4-cylinder, V-6 and V-8 configurations. If it were a vee, then at what angle? Barnard had said that if this configuration was chosen the injection pump, alternator and so on would have to be located within the vee. With their already established ideas for a 1.5-liter turbo, Porsche quickly discarded any ideas of an inline-4 and never even considered using a ftat-6 design.

Serious thought was given to a V-8 configuration but in the back of the Porsche engineers' minds was the fear that one day there would be a limitation on horsepower in Formula I. Their crystal ball was right, for the 220-liter fuel limitation introduced for the 1984 season effectively limited bhp in racing if not in qualifying. So the final decision was made in favor of a V-6 layout. Other factors that favored this layout were the importance of thermodynamic efficiency and minimizing friction losses. It would also allow them to make a short, stubby 4-main-bearing crankshaft and with Porsche expertise they could run two big-end bearings side by side on each very narrow crankpin. The small bearing surfaces made possible in a smooth V-6 outweighed the stronger 5-main-bearing requirements of the rougher inline-4 engine, adding to the overall efficiency.

The final factor to be decided was the included angle of the vee. To minimize the effects of the moment of inertia and achieve the highest possible degree of smoothness, any angle among 60, 90 or 120 degrees would qualify. To further the search for smoothness and balance Porsche experience dictated that an even-firing order was necessary for one bank of cylinders-because the exhausts of both banks would be connected this factor was not necessary in the second bank and bearing in mind thewidth limitations laid down by Barnard. an 80 degree vee was decided upon as the best compromise. Even with the change in regulations away from ground-effect cars, Porsche feels that 75 or 80 degrees is ideal and would still use the same configuration for a non-wing car. Porsche also feels that for the given capacity of 1.5 liters the V-6 layout is best but should the capacity be reduced in the future it would give serious thought to a 4 in line engine.

With configuration decided drawings were made of the engine block design. With this in progress, drawings for ancillary parts, and where they would be situated and driven, could come along at a later stage. Thoughts now turned to the next most important feature-the engine management system of fuel supply and ignition.

The Porsche engineers had two options open to them: They could follow the route chosen by BMW and use an electronically supported mechanical pump, or they could use a system controlled entirely by electronics. The latter was the one they really wanted to use but there was no such system perfected at that time although one was in the development stages for use in Group C racing. To go ahead in this direction required a deep-seated belief in the ultimate potential and successful operation of a fully electronic system, but this belief was shared by all those involved in the project at Porsche. To add weight to their feelings, the designers at Bosch also believed it could be made to work.

I stress the importance of the designers' beliefs for there were no hard facts upon which they could calculate its success. Although they didn't look upon it as a gamble, they knew they would have problems in getting it to work. Time was short, but they also developed a semielectronic system in parallel just in case things went wrong.

While all this was going on, Ron Dennis wasn't sitting around twiddling his thumbs; he was out looking for someone to pay the tab once Porsche came to the expensive part of the project-casting blocks, making crankshafts and so on. He found him in the person of Mansour Ojjeh, who had been a faithful sponsor of the Williams team for some years through his TAG company. In May 1982 TAG took full financial responsibility for the project and an agreement was reached for the TAG initials to be cast into the camshaft covers. Marlboro McLaren had its way too, obtaining exclusive use of the engine, now known as the TAG Turbo.

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