International race engine directory article
Toyota entered the World Endurance Championship arena at the 1983 Fuji 1000km, with a pair of locally produced Group C prototypes powered by factory supplied, production based in line four cylinder, single turbo engines displacing 2.1 litres. Those 4T-GT cast iron units were based on a five bearing stock block and featured an aluminium twin cam, two valve, twin plug head and a BMW Formula One style twin-entry turbocharger developed in house. The linerless 7.0:1 c.r. challenger was blown to 2.5 bar absolute and was officially rated ‘480b.h.p.’ Its chassis was a design of the Dome company, well known in Europe for DFV propelled Le Mans cars. The cars were constructed and run by the Tom’s and Ikusawa teams. Both outfits contested the ’84 Japanese endurance series, along with a works entry, and some encouraging performances were registered against locally based Porsche 956’s, though there were no wins.
In ’85 Dome fielded its own car and won the first round of the Japanese series, a 500km race at Suzuka. However, Toyota continued to be represented at only the Fuji round of the World title chase, with one notable exception – Le Mans. No less than five teams were now running Toyota-Dome 85C’s at home and Dome and Tom’s (a large Toyota tuning and competition concern) entered a car apiece for the French classic. Toyot admitted that its 2090cc engine 89mm x 84mm.), now featuring an engine management system fom Nipon Denso and rated 503b.h.p. at 7,600 r.p.m., was underpowered by Croup C1 standards. It looked to fuel economy and reliability. The Tom’s car finished a worthy 12th overall.
Both teams were back in ’86, to no avail. For the ’87 campaign (still home-based) Toyota established the Tom’s operation as a full works team: Toyota Team Tom’s. Engine development and preparation was still based at the Higashifuji Technical Centre. And there was a new four cylinder engine, the 16 valve 3S-GT, introduced at the ’86 Fuji 1000km race where it looked very strong. This was similarly based on a linerless iron stock block (the 3S-GT motivated Toyota’s Celica and Supra models), and with capacity of 2140cc it was raised as high as 680b.h.p. at 8,700 r.p.m.
Dome supplied a further development of its original chassis design and though a two-car entry for Le Mans was again fruitless, the upgraded Tom’s team won national events at Suzuka and Fuji and showed strongly in qualifying for the home World Championship event. In ’88 Le Mans saw two development (‘88C’) cars, both of which qualified just inside the top 10 and both of which finished, though again no higher than 12th, Meanwhile, back at base the Engine Research and Advanced Engineering Department was putting the finishing touches to a replacement 3.0 litre V8 twin turbo engine.
3S-GT
The 3S-GT Group C engine was designed under the direction of Takehisa Yamaguchi by engineer Okamoto, a one time production car engineer fully employed on the competition programme once work commenced in ’84. At first the unit was envisaged as a potent rally engine but it was switched to the Group C programme before it was ever rallied. Early on it hd been recognised that that the original Group C unit lacked sufficient power to tackle the likes of Porsche, a major drawback its production-based eight valve head. The replacement 16 valver reached the prototype build stage as a Group C engine early in ’86 and was first track tested immediately after Le Mans. The 4T-GT engine was phased out in late ’86 and a batch of over 50 ‘3S’ blocks was cast specifically for the ’87 race programme. The overall design of the engine followed that of the production unit retaining the standard bore and stroke and with even an unchanged combustion chamber shape, though the water circulation was modified: heat was of course the major adversary. Yamaguchi says he concentrated on the cooling of the combustion chamber and put a lot of work into detailing. Te piston was oil sprayed and, unusually, the turbocharger rotor shaft was water cooled.
Cast within Toyota specifically for the Group C programme, the linerless iron monobloc extened down from the deck to the level of the crank axis, with the crankshaft running in bearings supported by two-bolt cast iron caps. The lower crankcase was magnesium while the head was one piece aluminium, attached by 10 studs and closed by a magnesium cover. Steel ring head gaskets were employed.
Toyota subsidiary Taiho supplied plain main and big end bearings whie the nickel-molybdenum –alloy steel five bearing, four pin crank was forged by another subsidiary Aichi-Seiko (a steel company) and was machined at Higashifuji. It had conventional extended balancing webs and was fitted with a vibration damper from the outset. The flywheel was steel and was attached by eight bolts. It was sized to match a regular 7.25” racing clutch.
Fully machined I-section con rods and conventional (circlip retained) gudgeon pins were again of nickel-moly steel. Forged light allow pistons were produced by the local ART company and were of conventional flat-top, fully-skirted design, carrying three rings (two compression, one scraper) with the top ring moly-coated. The bore was uncoated. The piston had small valve clearance notches and the combustion chamber was of the conventional pent roof form with a single plug.
The head carried each camshaft in five plain bearings (again supplied by Taiho) and valve operation was normal, with bucket tappets and dual springs over (solid) steel valves. The drive was taken directly off a pinion at the front of the crankshaft by a Unitta (Japanese) belt that also powered oil and water pumps. A sandwich construction oil pump supplied by Aishin, yet another subsidiary, incorporated a scavenge pump for each end of the crankcase plus a pressure pump and also mounted on the front cover was the main water pump. A second water pump for the turbocharger was mounted on the head. Oil was cooled by a heat exchanger and the car carried separate water radiators for engine and turbocharger.
The twin-entry in-house turbocharger was of the CT44RT variety as developed for the 4T-GT engine by Yamaguchi’s department. Of conventional (KKK-style) design, it revved to 110,000 r.p.m. and offered up to 3.5 bar absolute. It was equipped with a mechanically-controlled wastegate system also developed by Toyota. A twin turbocharger installation had been perceived as too heavy but the single twin entry unit was run in conjunction with dual water cooled wastegates and this provided excellent response. The turbocharger was of a conventional design (for reliability) with aluminium compressor whell and Inconel turbine wheel in a high nickel iron casting. Maximum boost was set from the cockpit.
The compressor blew through an air:air aftercooler to the plenum chamber outrigged to the right of the block (the induction side). Each cylinder had its own throttle butterfly and a single injector was placed upstream of that. The solenoid injectors were supplied by Nippin Denso and were larger than the Bosch contemporary, and one per cylinder was quite adequate. Nippon Denso also supplied it’s CD-type ignition system (together with a 10mm plug for each cylinder) plus an integrated control system developed jointly with Toyota that governed ignition timing as well as running the injectors. There were two ignition pick ups on each camshaft, a system developed by Toyota for greater accuracy.
The Nippon Denso engine management system took r.p.m. (from the crank), throttle position, manifold pressure and charge air and block water temperature as its key inputs. The mapping process commenced early in ’86 with the prototype engine, the aim to produce a relatively ‘coarse’ map (a reading every 400 r.p.m., for example). From the outset the unit was run with a 7.0:1 compression ratio and by the time it was ready to race it was attributed a conservative 550b.h.p. race power on 2.4 absolute with as much as 750b.h.p. available for qualifying as manifold pressure was pumped up towards 3.5 bar absolute. Maximum r.p.m. was 9,000 with 8,500 r.p.m. the regular limit. The engine weighed 180kg. complete with exhaust, turbocharger and induction system and was reckoned to take 100 man hours to build from scratch.
From ’87 Toyota introduced a smaller CT44ST turbocharger offering 2.8 bar absolute maximum race boost, leaving the higher airflow RT unit for qualifying. The ST model was designed for greater reliability and at 2.8 bar the engine (with well developed software) produced in the region of 600b.h.p. Maximum output was officially quoted as 680b.h.p./8,500r.p.m. with torque 65m/kg at 5,500 r.p.m. though as much as 900b.h.p. had been extracted on the bench.
An important development for the ’87 season was an oil gallery piston, the hardware supplied by Mahle. An early valve seat headache was cured through the use of a special, undisclosed, material developed by Toyota. A spate of cylinder bore cracking arose early in ’87 and prior to Le Mans a new block casting was introduced with a 2mm greater wall thickness to cure the problem. By Le Mans ’88 around 200 3S-GT blocks had been produced for the Group C programme. The only significant modification for that event was the lower compression ratio of 6.5:1 in view of the relatively low octane fuel that had been supplied by the organisers the previous year.
3S GT
In line 4
89.0 x 86.0mm 2140cc Iron Block, aluminium head Linerless 5 main bearings, plain Steel crankshaft, 4 pins Steel con rods ART light alloy pistons Toyota rings DOHC belt driven 4 valves cylinder, 4 plug 50 degree included valve angle 36.0mm inlet valve 31.5mm exhaust Nippon Denso ignition Nippon Denso injection Nippon Denso engine management system Compression ration 7.0:1 Maximum rpm 8,500 140kg
Toyota Motor Corporation
Higashifuji Technical Centre
Engine Research and Advanced Engineering Department
1200 Mishuku
Susono-Shi
Shzuoka-Ken, 410-11
Japan
Article originally published in the International Race Engine Directory by Ian Bamsey, Haynes Publishing, 1989
