samedi 11 août 2007

Fiat 1500S, The Autocar, 18 December 1959


Demands of the American market have brought about a rather contradictory state of affairs in the European motor industry. Before the war most European manufacturers included open and sports models in their ranges, but there has been a gradually diminishing demand in the respective home markets for these cars, which in many cases were omitted from the emmediate post-war products. To meet the increasing requirements for sports cars in America, however, more of the larger manufacturers are again turning their attention to this range.

Significant of this trend has been the arrangement made between Fiat, Turin, and Osca, run by the Maserati brothers at Modena. For some time Fiats have had a sportscar in their 1200 range. Until the Geneva Show, when it was redesigned by Farina , it was rather ugly and did not enjoy large sales. More-over it was powered by a pushrod engine, relatively limited in power.

Apart from the improved efficiency which a twin overhead camshaft layout permits, there is also a big sales appealwith this type of engine; this feature has undoubtedly played a large part in the success of the Jaguar in overseas markets. To jump into this market and avoid the time penalty involved in designing and developing their own unit, Fiat concluded an agreement with Osca to produce their already developed twin-camshaft 1½-litre engine. Detail changes were made to assist production, but basically it is unaltered; the engines are now being produced at a rate of 50 per day at the Fiat Mirafiore factory. In fact the entire production is undertaken by Fiat, and Osca buy back engines for their own requirements and carry out detail modifications further to increase power.

Square proportion are used for the engine which has a bore and stroke of 78 mm. The cylinder block is cast iron, with five main bearings, and the joint is on the crankshaft centre line. The sump is formed in two pieces, with the upper half acting as a lower crank chamber, well baffled to eliminate oil surge. The sump proper is a comparatively shallow casting, externally ribbed. A feature now almost standard on Fiats is a centrifugal oil filter formed in the crankshaft pulley, as on the 500 and 1800 engines.
A single-stage chain drive is used between crankshaft and camshafts; these operate inverted bucket-type tappets, working directly in the aluminium cylinder head. The valves have an included angle of 80deg equally spaced on either side of the cylinder centre line.
A feature of the engine is a rather deep combustion chamber space which results in a noticeable dome and cut-outs for valve clearance on the piston crown, even for a quite modest compression ratio of 8.6 to 1.
The valve sizes are relatively large, with an inlet head diameter of 1.5 in, which gives a figure of 11.3 h.p. per sq in of inlet valve head area. On the Fiat engine the exhaust and induction ports are on opposite sides of the engine in the orthodox manner. Mixture is supplied from a twin-choke, downdraught Weber carburettor, the manifold being water-jacketed at the riser pipe. In this form the engine develops 80 b.h.p. net at 5,800 r.p.m.
This basic engine is developed by Osca for their own sports cars to give 100 b.h.p. A recent introduction has been a new design of cylinder head with, rather surprisingly, two twin-choke Weber carburettors mounted in the cleft formed by the two camshaft housings to provide vertical intake ports. In this form and with a higher compression ratio the power output is 120 b.h.p.

During the recent Turin Show an opportunity arose to sample a Fiat twin camshaft 1500 cabriolet. This car has identical dimensions with those of the 1200, except that the brakes are larger; in fact they are of the same size as is used on the 1800 and 2100 saloons. The body is of integral construction, a technique being increasingly used by the Italian specialist coachbuilders since it was developed succesfully by Farina.
As a result, the body is very rigid, and free from any shakes or tremors. The car is designed as a two-seater with no pretention to carry more passengers. Behind the individual bucket seats is a luggage platform, and the boot is surpisingly roomy if rather shallow; the spare wheel is mounted beneath the floor.

With the hood erected, which can be done very quickly with the assistance of simple and effective catches, vision is good. At speed the car is quiet and completely draught-proof, and the hood does not flap throughout the speed range. A bad feature in the hood construction is the use of a frame stick immediately above the passenger's head; a tall passenger, without the steering wheel to support him, found that his head made frequent contact with the hood stick on undulatingroads until he made use of the grab handle fitted on the dash. When folded away, the hood fits neatly into a recess in the body and is hidden by a flush-fitting cover.

As in many Italian cars, the driving position seems best suited to people of a rather small stature, so that a long-armed driving position is difficult to attain in conjunction with easy reach to the pedals; also the wheel protrudes well up into the screen area, in the manner of the Mercedes 190SL.

Road holding is good, with certain reservations. When the car is taken to the limit of adhesion on corners, there is pronounced oversteer which is reflected in the fact that on the straight, continuous small corrections must be made at the wooden-rimmed Nardi steering wheel to maintain a chosen line.

The ride is quite firm with, perhaps, too much damping of the bump, the passengers suffering from quite violent vertical movement at speed on a wavy surface.
During a short run the car was taken over the Col de Finestre, near Susa; a smaller turning circle would have been appreciated on the tight hairpin bends there, but the car handled very well on these rather rough surfaces. The brakes, which are fitted with a Baldwin Hydrabooster, were light and progressive. Rather severe use induced no fade, though they became slightly rough when hot.
Throughout its range the engine was very smooth. Piston slap could be detected, but this results, no doubt, from the use of pistons developed primarily for competition, and is not a serious criticism. The rev counter has a red band between 6,500 and 7,500 r.p.m. and the lower limit was reached regularly in the intermediate gears. Synchromesh is provided on the upper three ratios of the four-speed box and the change is quick, with relatively short movements. It was felt that the third gear might well be raised for a car of this character.
The car was not at our disposal long enough for performance figures to be taken, or even for speedometer readings to be checked. On one long stretch of main road, however, when the car was held ast maximum speed for a considerable distance, this instrument recorded 170 k.p.h. (105.8 m.p.h.) with the tachometer at 6,500 r.p.m. The manufacturer´s figures for m.p.h. per 1,000 r.p.m. in top gear are 16.1, which at 6,500 r.p.m. corresponds to 104,8 m.p.p., indicating that a genuine maximum of around 105 can be expected.

In summary, the integration of the Osca engine and Farina coachwork with Fiat suspension and production seems a happy compromise. It results in a vast organization being able to market a quality sports car for the equivalent of £ 1,000 in its home market. Without this co-operation it is doubful whether the production quantities involved would be an economical proposition for Fiat.

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