PRESENT-DAY RACING CARS THE 3.5-LITRE 12-CYLINDER ALFA-ROMEO

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PRESENT-DAY RACING CAI S

I. THE 34-LITRE 12-CYLINDER ALFA-ROMEO

the various racing cars which have made their first appearance during the past season none perhaps contains a greater measure of technical interest than the 31-1itre 12-cylinder Alf aRomeo. The first of these cars took part in public competition for the first time in the Italian Grand Prix which was run at Monza towards the end of May, and was the machine on which the late Luigi Arcangeli unfortunately met his death a few days earlier. Although the car did not succeed in completing the course, two machines of the same type again appeared at the Italian track for the Monza Grand Prix in September, and although they were both again eliminated before the end of the contest, they showed themselves to be extremely fast, and possessed of a far greater degree of stability and

controllability than might be supposed from a casual glance at the specification.

It is said that the car, which owes its design to the genius of Signor Vittorio Jano, had its origin as the result of what was intended more or less as a joke. During a discussion on the subject of how a really powerful racing car could be constructed with the famous 1,750 c.c. AlfaRomeo engine as a basis, somebody suggested that the best method would be to put two engines in one car. Signor Jano immediately interpreted this idea in his own manner, and the 12-cylinder racing car was the result. Briefly the machine consists of two 6-cylinder engines, each with its own clutch and gear-box, placed side by side in the same chassis, and driving the back axle through two propellor shafts. The engines are of the well-known Alfa-Romeo 6cylinder super-sports type with a bore and stroke of 65 x 88 mm., the total capacity of the two units thus being 3,495 c.c. These engines have a fairly low compression ratio of 51 to 1, the cylinder heads being hemispherical. The valves, of which there are two per cylinder, are made of cobalt and are of the flat-headed type, being mounted in the detachable head at an angle of 90° to each other. These valves are operated by overhead camshafts, of which there are two fore each engine, and which are driven by a train of helically cut pinions from the rear end of the crankshaft. Each of these camshafts is carried in five bearings, and the valves are closed by three concentric springs with a combined tension of about 28 lbs. The valve

timing is arranged to give a good degree of overlap, the inlet valves opening 5° degrees before top dead centre and closing 35° after the piston has reached the bottom of its stroke, while the exhaust valves open 45° early and close 13° late, the overlap thus amounting to 18°.

The cylinder heads and blocks are made of a special iron alloy, while the crankcases are of aluminium. The crankshafts which are machined out of the solid billet, are each carried in five plain bearings, with the camshaft drives at the rear, and the Roots type superchargers, which are of Alfa-Romeo construction, driven direct from their forward ends. The connecting rods are of H section, and the very light aluminium pistons are fitted with three rings and a scraper. Lubrication is attended to by a single geardriven pump, the dry-sump principle not having been adopted. The superchargers, which are effectively lubricated from the base chamber, each suck through a single horizontal-type Memini carburettor, the more complicated method by which the supercharger blows through the carburettor having been avoided, and are fitted with pressure relief valves which blow off if the pressure exceeds 8 lbs. Ignition is attended to by Bosch coils, the dis

tributors being driven off one of the camshafts of each engine, while the revolution counters take their drive from the other. These engines run up to 4,800 revolutions per minute, at which speed the combined power output is in the neighbourhood of 300 h.p.

Each engine is built up in unit with a dry-plate clutch and a 4-speed gear-box of cast aluminium.

At the back of each gear-box is a spherical universal joint, and thence the drive is taken by a propellor shaft enclosed in a pressed-steel torque tube to two separate differential gears enclosed in aluminium casings and mounted side by side. Tests were made with the car fitted with a solid back axle, but the results were not altogether satisfactory and it was finally decided to use the two differentials. Both engines revolve in the same direction and are positively geared together so that one cannot run faster than the other. The driver is situated in the centre of the car, between the two propellor shafts and has a gear-lever mounted directly on the top of its gearbox each side of him, the gear-levers being coupled together so that he can effect a change in both gear-boxes simultaneously with either hand. The steering wheel is, of course, in the

centre of the car, and controls each front wheel independently through a worm-and-wheel gear and two separate drag links, no track rod being therefore necessary.

Each wheel is fitted with a large brake drum, some 18 inches in diameter and 21 inches wide, made of duralumin and provided with linings of a special asbestos material. The brakes are operated by rods, the shoes being of the self-wrapping type and no servo-motor being employed.

Suspension at both front and rear is carried out by semi-elliptic springs combined with Hartford-type shock absorbers of Italian manufacture. Rudge-Whitworth wire wheels are used and are shod with 30 x 6″ wiredon tyres. The car has a short wheelbase of 9ft. 6ins, and the track of 4ft. 9ins., is not wide when it is considered that two engines have got to be accommodated side by side in the chassis, while the complete car in racing trim weighs only some 23 cwt. At Monza the cars were fitted with a back-axle ratio of 3 : 1 which gave them a maximum speed on the level of about 165 m.p.h.

The whole design is obviously one of exceptional interest and one may well conjecture that more will be heard of these cars in the not distant future.

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