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Ford's mini challenge
After an extremely thorough analysis of market trends. Ford have decided to reverse the previous decision against building really small cars. Because of rising costs, especially that of fuel, small cars are making a steady gain in their share of total sales. There is nothing half-hearted about Ford's entry into this sector, no attempt having been made to adapt the conventional rear-drive package. Instead, the completely new design follows that of its main rivals in featuring front-wheel drive, a transverse engine, and a hatch-back body style.
The body is a two-door four sealer with a large window area; as is usual with this configuration, there is a detatchable parcel shelf to hide the luggage and the rear seat can be folded to form an estate-type rear platform. The steel monocoque has no sub-frames, the suspension loads being transmitted through rubber bushes, which are not pre-loaded as that would reduce compliance and sound insulation. The MacPherson front suspension gives negative scrub geometry, as pioneered by VW-Audi, in conjunction with rack and pinion steering.
At the rear, a trailing dead axle on coil springs is located laterally by a Panhard rod. The two trailing arms have rubber bushes at both ends; thus, they cannot be used to absorb braking torque and the axle beam is not in torsion. The braking torque is fed into the outer tubes of the telescopic dampers, and these are fabricated with forward-facing arms that pick up vertical pegs, which are welded to the front of the axle tube. Rubber bushes prevent these sliding joints from rattling and this is certainly an unconventional solution. A separate anti-roll bar, behind the axle, is fitted to the higher-performance version of the Fiesta, to reduce the roll angle during hard cornering.
Front disc and rear drum brakes are used, with diagonal dual circuits. It is claimed that the pedal pressure is moderate, but an optional vacuum servo is offered.
As economy is so important in a small car, the Ford designers have very wisely chosen to build an engine with three main bearings instead of the usual five. The theory behind this was explained in my recent technical article, The Bottom End, but briefly there is a marked reduction both in mechanical friction and internal aerodynamic losses. The cylinder head and block are both of cast iron and the crankshaft is also cast, in nodular graphite iron.
The chain-driven camshaft operates the valves through pushrods and rockers. It carries the usual skew gear, but the distributor and oil pump are not on the same shaft The distributor is normally situated but the oil pump is external to the engine, its horizontal shaft carrying a skew gear which meshes with the bottom of the camshaft pinion. The valves are in line but inclined to give wedge-shaped combustion chambers, which are necessary for forthcoming pollution regulations but have no adverse effect on power production.
The engine of the Fiesta has the same water jacket spacing as the Kent series, but the bore has been reduced from 81 to 74mm. thus cutting the length of the unit by 30mm. Its dimensions are 74 x 55.7mm (957cc) and the two-star petrol version has a compression ratio of 8.3 to 1, developing 40bhp at 5500rpm. For 4-star fuel, a compression ratio of 9 to 1 gives 45bhp at 6000rpm. In addition, for the higher-performance model, a 65mm stroke increases the capacity to 1117cc which, with a 9 to 1 compression ratio, results in 53bhp at 6000rpm; a 1300cc version is promised for the future.
The engine is mounted crosswise, with a radiator of crossflow type installed ahead of it, the fan being electrically driven. Great pains have been taken to reduce servicing costs and the clutch can be removed and replaced very quickly, without disturbing the engine. The four-speed, two-shaft gearbox is in line with the engine, helical spur gears taking the drive to the differential This means one short and one long drive-shaft, which has proved to have no disadvantages in Fiat and other front-drive cars. When the more powerful engine is specified, the longer driveshaft has a harmonic damper clamped at its mid point, to eliminate torsional nodes. All the universal joints are of constant velocity type, the outboard joints being of the well-known Rzeppa construction.
Although the gearbox operates on a conventional ball mounting, its lower end follows a concealed gate. To avoid any inaccuracy in selection, a tubular member goes from the pivot point to the engine, thus keeping the distance apart constant.
The low-compression 957cc engine pulls a higher gear than the four-star version, in the interest of economy. Like the 1117cc unit, it gives 15.8mph per lOOOrpm in top, compared with 14.9mph for the more highly stressed 957cc type. Claimed maxima for the three Fiesta models are 80.7mph, 85.1mph, and 88.2mph, with DIN fuel consumptions of 41, 37.7, and 34.9mpg respectively.
Pressed steel wheels are normally fitted, but the top-of-the-range Ghia model has light-alloy wheels among its extra equipment Tyre sizes, according to model and customer options, are 135 SR-12ins, 145 SR-12ins, and 155 SR-12ins. This really is a small car, with a length of 11ft 8.4ins, and to give you an idea how small that is, it's 16ins. shorter than the Escort. The Fiesta is light, too, ranging from 15431bs to 16011bs for the Ghia. ,
In spite of the somewhat angular bonnet top, the Fiesta is claimed to have been designed in the wind tunnel and to have a low drag factor. It has an air dam in front, and the grille through which the cooling air enters has slats, which are shaped in aerofoil form. On these, an increasing boundary layer effect develops with speed, thus by-passing a major proportion of the air over the bonnet instead of inside it. This reduction is drag by automatically restricting the internal airflow is a very worthwhile exercise in aerodynamics and the arrangement is the subject of a patent
It is most refreshing to see a new car from Ford without the traditional live back axle. It shows that the team are capable of advanced engineering when given the chance. However, the sales performance of the old-fashioned Cortina proves that brilliant designs are not necessarily the best-sellers and we snail watch the success story of the Fiesta with great interest. It is a worthy contender in a tough section of the market. It will not be available in Great Britain until next January and no prices have yet been mentioned.
SPECIFICATION AND PERFORMANCE DATA
Car described: Ford Fiesta two-door four-seater saloon.
Engine: Four-cylinders 74 x 55.7mm (957cc). Compression ratio 8.3 to 1, 40bhp at 5500rpm, or compression ratio 9 to 1, 45bhp at 600Orpm, 74 x 65mm (1117cc). Compression ratio 9 to 1, 53bhp at 6OOOrpm. Ford downdraught carburetter Pushrod operated overhead valves.
Transmission: Single dry plate clutch 4 speed synchromesh gearbox with central remote control, ratios 0.959, 1.346, 2.050, and 3.583 to 1. Final drive by helical spur gears, ratio 4.056 to 1 for 957 LC and 1117 HC, 4.294 to 1 for 957 HC
Chassis: Combined steel body and chassis. Independent front suspension by MacPherson system with outside scrub radius. Rack and pinion steering. Trailing tubular dead axle with coil springs and Panhard rod. Disc front and drum rear brakes with diagonal circuits, servo optional. Steel disc wheels, light alloy on Ghia and optional, with 135 SR-12, 145 SR-12. or 155 SR-12 tyres. according to model and option.
Dimensions: Wheelbase 7ft 6in. Track 4ft 4.5in/4ft 4.0in. Overall length 11ft 8.4in. Width 5ft 1.7in. Weight 1543 to 160lbs.
Performance: Maximum speed: 957 LC 80.7mph, 957 HC 85.1mph, 1117 HC 88.2mph. Acceleration 0-6Omph: 957 LC 16.1s. 957 HC 15.0s, 1117 HC 13.7s.
Fuel consumption: 957 LC 41mpg, 957 HC 37.7mpg, 1117 HC 34.9mpg (maker's figures).
Top-Left - Soon to be a familiar shape - the three-door Fiesta follows recent f.w.d. hatchback trends.
Middle-Right - Below: engine and driveline configuration. A harmonic damper is fitted to the longer driveshaft on the larger engined model to eliminate torsional nodes.
Bottom-Left - Fascia of the comprehensively equipped Fiesta 'S'.
by John Bolster.