Some Advance Details of a Highly Interesting Four-Wheel-Drive Car in Preparation to Uphold Hill-Climb Championship Honours
The new Allard sprint car is to be a four-wheel-drive chassis, constructed almost entirely of light alloys and having an estimated weight of between 12 and 13 cwt. An air-cooled V8 engine of 4½ litres capacity will be used in conjunction with Clerk patent electrically-controlled epicyclic gears so arranged that the torque to each wheel is under the driver’s control. The wheelbase will be 100 inches with front and rear track of 56 inches.
Mr. Robert Clerk of Richmond, Surrey, has been responsible for the detail design, and especially that of the electrical transmission system.
The frame will consist of two parallel duralumin tubes of oval section, joined by five cross-members, these being dural tubes of 5-in. diameter. Front suspension will be by unequal-length wishbones carrying fully-floating hubs and the rear axle of de Dion type, located by a central slide and radius arms to the centre of the frame. Lockheed suspension struts will be used front and rear, as on the B.R.M.
The original design called for an entirely new engine, with a magnesium-alloy crankcase, aluminium heads and cylinder barrels, and duralumin connecting rods, which would have given an estimated saving in weight over the present Steyr engine of some 100 lb. Manufacturing difficulties in the short time available, however, leave no alternative to using a Steyr crankcase and crankshaft, with Wellworthy Al-Fin barrels, Specialloid pistons and re-designed connecting rods and cylinder heads, together with Lucas ignition and Amal carburetters, and it is hoped to achieve a power output of 250 b.h.p. at 6,000 r.p.m. This is not an impossible figure when one considers that the present Steyr, with 79 mm. bore and compression ratio of 11 to 1, develops about 165 b.h.p. at 5,500 r.p.m., and that the new barrels and heads incorporate a bore of 88 mm., compression ratio of 12.5 to 1, and larger valves with much improved breathing characteristics.
The transmission system has been especially designed to provide some control over the power transmitted to the front axle in relation to the rear. For many events (dependent on the venue) it is proposed to have two speeds only and accordingly the three-speed-and-reverse auxiliary gearbox behind the engine can be removed. When this gearbox is used, in conjunction with the gears in the axles, four forward speeds and reverse are provided, with two-speeds to the front axle.
Both axles are the same, and the ratio of the rear axle only is changed when the gearbox is fitted. The driving mechanism in each axle consists of the usual crown wheel and pinion and two sets of electrically-operated epicyclic gears which provide the two speeds previously mentioned. There is therefore a total of eight sets of epicyclic gears, two to each axle shaft, and these units also incorporate separate clutches, there being no conventional clutch between engine and transmission. The differential action between each pair of wheels is obtained by varying the current supplied to the near or off-side epicyclic gears in each axle, this control being effected by an automatic switch actuated by cams on the steering column. The same principle of control is also used between front and rear axles, and although the norma maximum torque transmitted to the front is some 40 per cent. of the total, this can be reduced as required to suit prevailing conditions by a manual control fitted close to the driver’s left hand. Gear ratios will be 3.5, 4.18, 5.47 and 7.65 to 1, with estimated speeds of 125 m.p.h. in top, 110-115 m.p.h. in third, 85-90 m.p.h. in second and 60 m.p.h. in first gear. Tyres will be 5.00 by 18 mounted on magnesium Z.5.Z. alloy wheels.
Brakes are 10-in. hydraulically-operated, and mounted inboard on the axle cases. The axle shafts are all interchangeable and consist of a Layrub coupling on the inside and an open Hardy Spicer joint at the wheel. In view of the light weight of the car, it has not been considered necessary to use constant velocity joints with their unavoidable increase in weight. Layrub joints are also used on the propeller shafts.
Steering is by rack and pinion, with the box mounted in the centre of the frame in front of the engine, and the steering column passing between the two banks of cylinders.
A single-seater body will be fitted, probably with alternative sizes of petrol tank, but these final detail items have not yet been settled.
Light alloys have been used everywhere possible. The frame, wishbones, suspension supports, hubs, drums, brake fittings, steering rods and idler wheel, radius arms, etc., are of duralumin or similar alloys, while the newly developed magnesium Z.5.Z. (Zirconium) alloy is used for the wheels, gearbox, differential cases and steering box.