A Mood of restraint
Last month’s road test , the Mazda 4×4, was the second of the top Group A rally contenders of the moment, after Lancia’s Integrale. This month we complete the trio of road-going turbo 4WDs by looking at the Toyota Celica GT-4,which has just gone on sale in this country.
British buyers have had the smooth 2WD 148 bhp Celica on their lists for some time, and the practicality and performance of the £16,720 coupe have found it many customers. In Japan the turbo version with a third more power and twice as many driveshafts has been on sale for over a year, but running exclusively on unleaded fuel has had to wait for the recent shift in oil-company attitudes in Britain to be included in Toyota GB’s range. This is believed to be the first car to go on sale in Britain in catalyser-only form, thus running exclusively on unleaded fuel, as opposed to simply being compatible with the stuff.
The huge expansion of unleaded outlets in the last twelve month has finally made it realistic to drive an unleaded-only car , but the be on the safe side Toyota GB includes a green five-litre spare fuel-can, filled with Explosafe safety fuel.
Outwardly similar to the Celica GT twin-cam, the 16-valve engine in fact has numerous modifications apart from the turbocharger itself. The block is strengthened, and crank, pistons, rods and timing belt have all been changed to cope with the higher stresses of an engine producing 185 bhp, nearly 40 up on the unblown car. with the ever-cleverer electronics listening out for any knocking and constantly fiddling with the ignition timing and the boost pressure, the engine is able to run at a compression ratio of 8.5:1, and the black box also manages the fuel pressure to obviate the effects of high fuel temperatures which can upset turbo engines.
Although the specific output of the 3S-GTE engine is not exceptionally high by today’s standards at 92 bhp/litre, Toyota has concentrated a great deal of thought into the dissipation of heat. Intake air-coolers are becoming common on turbo cars, but this one is itself water-cooled, with its own pump and small radiator to dispose of the heat. Such a system is easier to cram under the crowded bonnet than the large box of a conventional air/air unit. Engine oil is cooled in an oil/water heat-exchanger plumbed into the main engine cooling circuit in much the same way as the Ferrari Dino, and to avoid compromising the main system the water-pump is uprated by 10%, the fan by 50%, and the radiator becomes a double-core unit with 30% greater heat dissipation.
Piston temperatures are also kept under control by oil jets located low in the bores, which at high revs direct a cooling spray onto the underside of the piston crowns. Unusually for a new turbo engine, Toyota has not gone for water-cooled turbine bearings, relying instead on increased lubrication flow to stave off that critical moment of overheating just after the engine has been switched off.
Although taking drive to all four wheels from a transverse-engined car once looke a complicated problem, the various solutions have proved straightforward and efficient. Toyota uses a similar gearbox package to the 2WD car, with the gearbox on the end of the engine. The output shaft drives the centre differential, which is parallel with the main-shaft and is bridged by a viscous coupling.
Helical gearing from one of the central outputs turns the front differential, and bevel gears from the other turn the take-off through 90deg for the rear prop shaft. These transfer gears are fitted with a dynamic damper to cut down any noise. Torque is split 50/50 between front and rear, though because of the step-down of the transfer gears, the rear axle has a 33% higher ratio than the front. The rear diff is not mounted direct to the body, but first to the suspension members, which in turn are attached to the shell by absorbant mounts. Neither front nor rear diff has a limited-slip facility.
The whole package is remarkably neat and slips under the bonnet without any loss of passenger leg-room. Indeed there is no noticeable change from inside, though the floorpan has been has been strengthened. Each corner retains the Celica GT’s MacPherson strut with its paired lower links, but the spring rates have gone up and more damping is applied at the back.
Power steering is standard, but with the large steering wheel it is a bit insensitive; like the 2WD Celica GT, the GT-Four tends to over-react to steering inputs by rolling rather sharply, which makes it feel less stable than it actually is. With less assistance and more feel, the essentially fine balance of the chassis would be better displayed; there is no doubt that the adhesion is there, with a small and consistent amount of stabilising understeer to make the car easy to drive quickly. One of the benefits of 4WD is that tyres can be narrower for the same traction, with consequent superiority in wet weather, and the Toyota runs on the 205/60 VR 14s, which seem to have become something of an optimum choice from anything from family cars to super-sports-cars like this.
The momentary diagonal pitch when turning in to a bend is a mild annoyance which does not affect the actual road-holding, but the GT-4 would be that much more comfortable without it. It can be the sign of a conflict between front and rear roll stiffness, so it would be interesting to disconnect one or both and try the result.
With gas-pressured struts, there should be no change in the ride even after a pummeling over bouncy roads and the Toyota retained its firm characteristics throughout an afternoon of crossing and recrossing the patchy tarmac and sudden crests of the Army’s Salisbury Plain access roads. Some of these brows were very sudden, but the suspension never ran out of travel, nor did the brakes fade away into smoke. Unusually the rear discs are larger than the fronts, but that is because the fronts are ventilated, and the viscous coupling does not interfere with ABS, standard on the GT-Four. With stiffish suspension it is quite easy to start to lock a wheel over a crest, but the anti-lock tickles the brake pedal to tell the driver that he has reached the limit – an invaluable reminder.
Air-conditioning is included, as are electric windows (with an auto facility for the driver), a tilt/slide electric sunroof and centre locking. Tyre noise is evident from 50 mph and above, and as the speed rises there is also some whistling from the frameless door glasses. Neat points with technological sales appeal are the electric adjustment of the lumber provision and of side-bolsters on the back of the deep seats. Lift the lid of the central armrest and another clever detail is exposed: as well as covering a useful pocket, the lid separates to form a cup or bottle holder.
Large clear dials with orange needles on white figures dominate the instrument nacelle, and the GT’s battery gauge is replaced by a turbo boost gauge. Normally I see little use for this item, but here it has the wrong effect, drawing attention to the delay between demand and supply. For this is not the state-of-the art in turbo engine performance: there is a distinct pause while the revs creep round to 3500 before the action starts. Throttle is quick enough, but the unit is very flat below the critical point.
This makes town driving a chore, with many gearchanges needed to keep engine awake, and the gearing is excessively high. Top is an overdriven 0.731, and fast cuising in top means that the revs are well below the take-off point, giving no real punch. Fourth or sometimes third are definitely on the agenda for a quick dash past a caravan, which means a pause for a gearchange plus a pause for the turbo to take a deep breath.