Cars and Car Conversions - Technical: Fiesta Engine Tuning
"How good is the Fiesta?"
February 1977



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Technical: Fiesta Engine Tuning

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Paul Davies looks at the power potential of the new Ford.

This month the Ford Fiesta will go on sale in Britain. For the manufacturer it's probably their biggest gamble yet; a baby car of the sort that a few years back they said they would never build because of low profit margin, launched into a market already seemingly over-ful with small cars ranging from the ageing Leyland Mini to the advanced VW Polo. There's little doubt the Fiesta will succeed, Ford rarely get their sums wrong and this vehicle looks to have several advantages over its rivals not least of all being that it is competitively priced and will have the backing of the immense world wide Ford sales machine. There are going to be a lot of Fiestas around the world in next to no time.

The car itself you'll have to read about in the weekly comics and even some of the more boring monthlies. No doubt the road tests and comparisons will stretch from Lands End to John O'Groats before the motoring press have finished with this one - indeed we will give you a few brief driving impressions before too long. But while others have been waiting for Ford in this country to release press cars or trying to beat everyone else to it by slipping over to the Continent to drive a left hooker we've been up to something far more important.

With front wheel drive, compact size, low weight (at 700kg only 50kg heavier than a Mini) and a relatively low purchase price the Fiesta is destined to play a big role in motor sport. It won't replace the Escort at International level but for the clubman It looks certain the Fiesta will become just as important as the Anglia and Mini have been in the past. Ford already have their S model, Rallye Sport parts are on the way and before too long we're likely to see a 1300GT version. In addition virtually every tuner in the land is going to be offering equipment for the new baby Ford. So, while others have been playing, we've been getting down to the nuts and bolts and assessing the competition potential of the new engine and transmission.

The Fiesta engine is new. It's a development of previous Ford four cylinder engines, but it's almost entirely new. It's also without doubt got tremendous potential. Power outputs in the region of 100bhp per litre are likely without need for any major redesign and it would seem that all the weak points of previous Ford four cylinder units have been overcome. In fact Ford appear to have got almost everything right from the start.

The Fiesta engine is all iron. The block is bored to 74mm in all units and 55.7mm and 65mm stroke cranks are used to achieve the two standard capacities of 957 and 1117cc. With compression ratio of 9 to 1 the smaller engine develops 45bhp and the larger 53 bhp. The cylinder head is of crossflow design and a single choke Ford carburettor is standard equipment. The transverse mounted engine drives the front wheels through n separate gearbox and drive shafts with constant velocity joints at each end.

That is the basic specification of the Fiesta power plant. It's the details that make such good reading for the motor sport man.


The crossflow head is of extremely good design. It's eight port and has the ideal combustion chamber for a power producing engine. In plan the chamber is very much like the classic heart shape of the good old Ley-land A Series engine but the sharp peak opposite the plug (the one all Leyland tuners remove as a first stage to good combustion) is left out.

The chamber is also wedge shaped (like an Imp) which allows the valves to be inclined at 1 5 degrees to the vertical and also gives an extremely good squish area directly opposite the plug. The wedge shape leans towards the inlet port, which is already angled in the head, resulting in an extremely good flow from carburettor into combustion chamber. In addition with inlet valves of 38.5mm diameter (1117cc engine) and exhausts of 29.1mm there seems very little point in going up on sizes to achieve power outputs in the tOObhp region. Although it must be added that the usual Ford bi-metallic valves are used and so the material is likely to need changing at such levels.

As far as the head is concerned there are only a couple of little problems for the tuner. Although it's nicely angled the inlet port does have the disadvantage of a 15 deg kink at a point about half way along its length in the head and although at this point the port is nicely round (29.5mm) it changes to a rectangular shape at the inlet manifold face. Here the shape is 29.5mm x 20mm and unfortunately there's not enough space to machine it completely round.

The head deck is nice and thick and should take skimming of up to 2mm without problems. Reverting from Metric for a moment I'll add that 0.050in off the head face should equal a compression increase of one.....