1987 TAG – PO1 1.5-litre V6
1987 TAG – PO1 1.5-litre V6: Porsche renowned for its racing engine expertise. Since its work as consultants to Auto Union and Cisitalia, however, Porsche had been designing and building engines on its own account. Key to its successful work in this field since the 1960’s was the expertise of Hans Mezger, who made major contributions to the type 753 of 1962 and the type 912 engine used in the 1969 type 917. Mazger’s talents were given a new challenge in the 1980’s when Porsche was asked by a customer to design a Grand Prix engine. With first Renault (1977) and then Ferrari (1980) demonstrating the advantage of 1.5-litre turbocharged engines for formula 1 racing, the McLaren team realized that it would have to leave the naturally-aspirated ranks and look for a turbo of its own.
Since October 1980 McLaren – originally established by driver Bruce Mclaren in the 1960 – had been virtually a new company, McLaren International, under the direction of part-owner Ron Dennis, a fellow director was engineer John Bernard. When turbocharging was considered Porsche had to come into the frame, not least because the Stuttgart company had pioneered in the Can-Am series and endurance racing. After the first contact was made by McLaren on 26 August 1981, Porsche carried out a 4-month initial feasibility study for a new Formula 1 engine. Completed in May 1982, this was followed by a full contract, which was financed by a Saudi Arabian company managed by McLaren´s ally Mansour Ojjeh, Technique d’Avant-Garde or TAG.
The resulting engine was thus identified as a TAG unit and given the designation TAG-PO1. Its cylinder dimensions were established as 82 x 47.3mm for 1499cc. First run on the test bench on 18 December 1982, the engine was ready to compete in 4-GP’s in the autumn of 1983 in a provisional McLaren chassis – outings that were declared as tests, not serious entries. In its first full season, 1984, Porsche-designed unit took Niki Lauda to the drivers world championship ahead of Alain Prost in a sister car. It was Prost’s turn to win the championship in 1985, and he did so again in 1986. he had to settle for 4th in 1987, the last season in which the TAG-engine was used. From 1984 to 87 the McLaren-TAG's won more races than any other team.
The engine that made this possible was by no means a cost-no-object exercise. It was built by Porsche to TAG’s strict budged and specification. As well, it was planned by Porsche to fit snugly within a central underfloor channel at the rear of a new car which was planned to generate record high levels of downforce. Before this could be built, however, the racing authorities introduced new rules requiring GP cars to have flat-bottoms. Thus some of the engine’s features, such as high-placed exhaust pipes and a narrow crankcase, became redundant.
A V6 configuration was chosen in preference to the more costly and complex V8 alternative. Hans Mezger set its banks at an 80 degree included angle, narrow enough to allow room under its sides for the (planned) venturi tunnels yet wide enough to accommodate the central induction piping. His analysis of the first – and second – order vibration forces that the engine would generate showed that an 80 degree vee was a good compromise between the two. The angle also suited the expressed requirement for the engine to mount in the chassis as a stressed member, using the same attachment points as the Ford-Cosworth V8.
The PO1’s cylinder block was compact, its deeply-ribbed casting extended down only to the crankshaft centerline and up to the detachable cylinder heads. They and the rest of the engine’s major housings were cast of aluminum alloy by Honsel Werke AG. Inserted into the block were wet cylinder liners of aluminum, their bores coated with Nicasil, a Mahle-developed hard-wearing plated surface of nickel carrying silicon carbide particles. Long-time Porsche partner Mahle also supplied the aluminum pistons, which had an internal gallery through which oil flowed to cool the crown and ring lands. Lightly concave to provide a compression ratio initially of 7.5:1, the piston crown had cut-outs for TDC valve-head clearance. For the 1987 season compression was upped to 8.0:1. 2 compression rings and 1 oil ring were carried above the gudgeon pin. connecting rods were made of titanium, both pistons and rods were made more robust for final 1987 season.
The large bore allowed the 4-valves to be inclined to the left and right at modest angles. Inlet inclination was 14 degrees from vertical and exhaust angle was 15 degrees. In addition the valves were angled slightly in the fore and aft direction to give the chamber a slightly spherical surface and to improve the gas flow in the chamber. To permit this, the tappets were similarly angled and the cam lobes were given a conical profile. (A note here, it should be noted that this was 1987 well ahead of the 3l V10 era when such cam grinds started to be used). Diameters of the Glyco-made valves were 30.5mm inlets and 27.5mm exhausts.
Hollow stems in the Nimonic-steel valves contained salts that accelerated their internal transfer of heat away from the head to the stem and thence to the valve-guide. Extraction of heat from the exhaust-valve seat was significantly improved by tiny drillings that allowed water to circulate through the metal around the seats. A system patented by Porsche, this had its own pipework taking 10% of the water-pump output.
2-coaxial coil springs closed the valves, which were opened by inverted-cup-type tappets. Twin camshafts in each aluminum head were driven by a train of gears from the crank nose. Turned by an idler above the crank nose, the first half-speed spur gear for each cylinder bank also drove a water pump mounted on the face of the PO1’s front cover. Both rotating clockwise, the pumps delivered coolant to the centre of the vee to a manifold cast into the cylinder block, and to the previously-mounted exhaust-seat cooling system. Water flowed back along the cylinder liners, up past the exhaust valves and out through passages on the inlet side of the head. Magnesium was used for the pipes to the water pumps and from the heads.
Also mounted on the front cover were the scavenge and pressure oil pumps. These were placed at the front instead of in the increasingly-popular side-mounted location, as pioneered by Cosworth’s Ford V8, in order to meet the objective of a narrow crankcase that would offer minimum obstruction to an underbody venturi. Tunnels along the sides of the sump casting collected oil flung from the crankshaft and fed it to the scavenge pumps, the pressure oil feed to the crankshaft was through the nose of the crank, as had been Porsche´s racing practice since the type 753 flat 8.
Made by Alfig Keesler, the nitride-steel crankshaft had the straightforward layout of 4-main bearings and 3-rod throws – with side-by-side rods – that was pioneered for the racing V6 engine by Carlo Chiti’s 1961 120 degree vee Ferrari. Fully counterbalanced, it was carried in Clyco thin-wall lead-bronze bearings, as also used for the rod big-ends.
Although with the 80 degree Vee angle this did not provide equally-spaced firing impulses, the uneven timing could easily be accommodated by the Bosch Motronic engine management system. At Bosch Dr Udo Zucker headed the team that progressively developed the TAG engine’s control system. By 1985 all the control elements were combined in a single package, which - at a time when fuel consumption was critical - could tell the driver how many laps he could complete with his reserve of fuel at the boost pressure he was running. The final Bosch MP1.7 system used 2-solenoid-controlled valves, aiming at 30 degrees down into each inlet port, to inject fuel volumes that varied according to a highly detailed map of engine speed plus such factors as humidity, altitude, torque and engine deceleration or acceleration. Throttle control was by individual butterflies above the injection nozzles.
Long-time Porsche partner KKK supplied the engine’s twin turbochargers. Frustratingly for perfectionist engineer John Bernard, KKK took a year and a half to produce mirror-image units that allowed him to improve exhaust-gas flow to the right-hand turbocharger. Porsche’s own wastegates, finned for cooling, provided boost pressure control in the exhaust manifolds just upstream of the turbine entries. The turbo-compressors delivered through air-cooled intercoolers to individual plenum chambers feeding each cylinder bank.
The policy of Mclaren and Porsche was to run essentially the same engine in qualifying and the race. Three different turbines and two compressor types were available for the HHB model KKK turbochargers, these could be mixed and matched to tailor the set-up to the circuit, with the larger turbine giving more power but at a sacrifice in throttle response. Typical power in racing trim was 820bhp@12000rpm with a boost of 36psi. Maximum torque was 390 lb/ft@8800rpm. With a higher qualifying boost of 41 psi the V6’s horsepower exceeded 900.
The engines ran on a special toluene-based petrol developed by Shell. High reliability helped Porsche fulfill its TAG contract with remarkably few engines, only 15 were used in the first full season and a mere 50 or so for the entire program. In relation to the resources expended the project was a resounding success.
Stroke/bore ratio 0.58:1.
Compression ratio 8:1.
Con-rod length 115mm.
Rod/crank radius ratio 4.9:1.
Main bearing journal 48mm.
Rod journal 45mm.
Inlet valve 30.5mm.
Exhaust valve 27.5mm.
Inlet pressure 3.48 Atm.
Engine weight 150kg.
Peak power 860bhp@12000rpm.
Piston speed corrected 24.5m/s.
Peak torque 529 Nm@8800rpm.
Peak bmep 645 psi.
Engine bhp/litre 573.7 bhp/litre.
Engine weight per bhp 0.17kg/bhp.
"For every complex problem there is an answer that is clear, simple and wrong." H. L. Mencken
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