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Cars and Car Conversions - Technical: Rally Fiesta Development
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March 1979
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Technical: Rally Fiesta Development




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.....Ferguson, the company responsible for major strides in four wheel drive and notably the commercially unsuccessful but technically impressive Jensen FF, were commissioned to develop a totally new differential which Boreham are most reluctant to discuss in detail and which no doubt is one of the major keys to the viceless behaviour of the competition car. A unit was required which did not lock-in and lock-out violently according to engine load (anyone who's driven a rally Mini with LSD will be only too aware of how alarmingly unpredictable, time-consuming and muscle-building such antics can be).

The unit also had to be very compact since the Fiesta differential fits inside the gearbox casing, in-line with -the east/west engine - it is scarcely bigger than an average size cup and saucer.

From a blank sheet of paper Ferguson designed a totally novel unit, described as a speed-sensitive rather than torque-sensitive device related to the speed differential between two output shafts. Two were made initially, being first tested at the end of July last year; six more arrived in time for the Monte Carlo Rally in January.

However, while all these various developments were taking place, John Taylor had begun testing with a car that was basically standard aside from the substitution of a 1700cc pushrod engine and the new Hewland gearset. With no prior experience of the car, spring and shock absorber settings were based on information gleaned (by hook or by crook) from Saab, Ley land, and Dunlop. Thirteen inch wheels were adopted immediately to enable the car to make use of all Dunlop's existing tyre moulds for this wheel size and also to aid accommodation and cooling of the much bigger brakes that would obviously be required.

From the outset it was obvious, in John Taylor's own words, that the thing "went round corners like sh . . off a shovel" and it became equally obvious that the tiny brakes (drums at the rear) were totally inadequate for competition. Secure location of the engine also proved to be vital (subsequently further modified), and the lower ball joints on the front suspension required immediate strengthening.

John Taylor's patient and objective assessments of the car began to reveal the critical nature of ride height, the need for negative camber on the front wheels and the favourable response to the use of convex tyres (ie: the rallycross A4 type as opposed to the flat tread and vertical side wan of the A2).

On June 26th last year, the development car, incorporating some of the lessons so far learnt, plus a prototype of the G2 front suspension put together by Len Bailey, took its first bow courtesy of John Taylor.

Front suspension arrangements along with transmission modifications were obviously the critical areas, the secret of ease of control being provided by correct geometry; exactly the right wheel offset combined with "negative scrub steering".

To achieve the correct solution, a specially reinforced wide-based triangulated wishbone assembly was designed. These tubular "wheel location arms" which replaced the standard bottom arms, together with new aluminium uprights, front hubs, uprated ' bearing assemblies, and carriers plus a new front anti-roll bar with revised support brackets are a pleasure for an engineer, or anyone with some appreciation of mechanical finesse, to behold.

Heavy duty ventilated disc brakes of 266.7mm (10.5") diameter and 20.6mm (0.81") width with four po' calipers complete the picture at the front; while at the rear, smaller sized ventilated discs adorn the dead axle, accompanied by a hydraulic/mechanical handbrake caliper - all G2, of course!

Fiesta rear suspension is comprehensive, even in standard form, employing radius arms and a Panhard Rod. G2 modifications have included reinforcement of the axle, uprated wheel bearings and hubs, additional brackets for the disc brake calipers (two pot variety) and tubular radius rods located by the familiar rose joint/heavy duty bush arrangement seen on Escorts for many years.

This then was the basis of Ford's G2 Fiesta chassis package for Monte Carlo.

Hitherto, the car had used the standard)!) short but equal length driveshafts without trouble (until the ride height was raised) but the advent of Len Bailey's new suspension package called for the substitution of the short auxiliary shaft and its attendant steady bearing with one long driveshaft, giving vastly unequal driveshaft lengths. No one knew whether such an apparently lop-sided arrangement would pose problems, but it certainly saved weight and complication. Testing proved the sceptics wrong once again.

By August, John Taylor in the hack development car, had already succeeded in lapping a one mile quarry near Maidstone within one second of his Burmah Rally RStSOO's best time. Bumpsteer was providing him with plenty of work at the wheel, but since at that time the car was shod with six inch rim Escort wheels of incorrect offset, there seemed little cause for panic. However, the triangulated wishbone arrangement was redesigned, and just prior to Ford's shutdown strike, the revised wishbones and correct offset wheels met on the same chassis for the first time.

Roger Clark was then introduced to Fiesta at a testing venue near Grantham. He brought with him his ex-Cyprus rally-winning RS1800 and failed to approach John's Fiesta stage time in the Escort, albeit in very bad weather. However, the former was now suffering severe bumpsteer and the new high ratio rack was thought to be the cause. Time was running out... a decision on Monte Carlo looming.

John's hard worked hack was summarily cannibalised and rebuilt into a Monte specification car in order that testing miles should be accumulated on a full G2 package. Bumpsteer was once again proving to be a major stumbling block although in other respects the little car was showing enormous potential.

The problem was eventually solved thanks to a decision taken back in April (and not completely implemented until the beginning of December) to build a BDA powered version of Fiesta as a test bed in ' order to deliberately overtax components and discover weak links in the power train. The car was completed using a 1700 iron block/alloy head arrangement (primarily to save time) and produced a creditable 225bhp.

This ferocious beast, equipped with the G2 "kit" was taken to MIRA and in the course of setting some tarmac lap times which some other British rally teams would be truly horrified to discover, the trouble was pinpointed. Raising the ride height, which was required anyway, transformed a niggling fault with which it was possible to live, into a 225bhp driver's nightmare. The car became virtually uncontrollable and the new high ratio steering rack plus insufficiently rigid engine mountings (the latter allowing the BDA to move about in the chassis giving rise to "torque steer") contributed to the situation.

After an all-night session back at Boreham, Ari and Roger drove the car the following day, the former on his first acquaintance with it - both were highly impressed, describing the effort required to drive it (this with 225bhp remember) as no more than that of a 1300cc road car!

John Taylor describes the machine as an F1 car compared with an Escort: "it's very sensitive to change in all departments; either springs, shock absorbers, roll bars, toe in, toe out .... 10 pounds on the spring rate changes the handling characteristics completely, but it's comparatively easy to tell what's happening and your diagnosis is more often than not confirmed on the stop watch.

"If you wind on too much lock, you simply kill the car's speed; you can't drive it like an Escort; chucking it about doesn't help at all. You must drive it round corners, get it to turn in early - very unspectacular really, but very quick!

"Yes, I've learnt to left foot brake ...." a wry smile .... "it certainly helps!"

What in fact had been achieved was this: in the space of six months since the first near-standard prototype had turned a wheel, Boreham and friends had succeeded in developing a 1600cc pushrod Fiesta to the point where it was as quick on loose or tarmac surfaces as a forest specification G4 RS1800 - a feat which even the men involved initially found hard to believe.

Gradually the mental barriers built up against Fiesta were beginning to crumble. One can't imagine such a project being handled so successfully by any other motorsport department in the country, and when one has witnessed the superb detail work of the car at close quarters, one's admiration and respect for the engineer/mechanics who work at Boreham is further enhanced.

When the time factor is considered in relation to the activities of the department during this period, and the damaging effect of the Ford strike, it's difficult not to be impressed.

So why does Fiesta apparently work so well, where others before it have failed? One reason must surely have something to do with weight. Fiesta's homologated weight in G2 is just 775kgs, a figure that John Griffiths feels confident of achieving, given a little more time. Monte Carlo rally cars nevertheless still weighed-in at an impressive 810 kilos (1782 Ibs) giving a power to weight ratio of 201 bhp per ton; very similar to a forest Escort.

The weight bias works out at about 57 percent front, 43 percent rear; again similar, though more pronounced, than that of the Escort. Weight distribution is very much of an experimental area at present; John Griffiths adopting the common-sense maxim that if you mount as much weight forward as possible, then it is much easier to move items to the rear rather than vice versa should redistribution prove necessary.

Experimental areas abound. Ford left for the Monte with very limited information on differential oil temperatures; would the gearbox require a cooler? There had also been next to no time to prepare the car for ease of servicing. No one knew exactly how long it would take to change the gearbox/differential unit (which demands removal of the sump guard and the wishbones) under rally conditions; or indeed when and where such an operation might be necessary. Monte Carlo, then, was very much of a gamble for Boreham, but one which Peter Ashcroft felt fully justified in taking. As he says, "By RAC time, we shall have some of the answers."

Monte Carlo Fiestas eventually used modified G4 Escort pedal boxes after initially using revised Fiesta types. It is hoped to revert to modified Fiesta versions as soon as more time is available for development.

The standard of workmanship on the rally car (Ari's was built in Germany) was as one would expect from Boreham - exceptionally high. The way in which the department have sidestepped the hatchback's indigenous firewall sealing problem by moving the petrol tank to the rear along with the engine oil tank and double glazing the rear window with the addition of an extra bulkhead is very neat.

This year, with Roger Clark driving the G2 1600cc car on Sedan Products Internationals and John Taylor expected to be shaking up Castrol/Autosport crowd with a G5 BDA version, Fiesta will certainly be in the news.

Most of us said it wouldn't work when the idea was first mooted, and obviously there must be a limit to how much power can be transmitted to wheels that are also being steered .... but if that limit has not been found at 225bhp, then where the hell is it!?

Peter Ashcroft confidently expects to be able to homologate an all-alloy two litre BDA version in G4 if necessary .... to quote an opposition jingle, Ford Fiestas are being "built to win you over".