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Unleaded fuel - the Facts...

This article was written by lan Coulson Aff.I.M.E. Technical Advisor at Capri Club International (written circa 1999 but the contact information is up to date as of Jan 2021):-

Engines that were designed and built to run on 4 star leaded petrol, which includes virtually all Capri engines, will be damaged if run continuously on unleaded petrol. The reasons are twofold:

Firstly, unleaded petrol burns at a much higher temperature than 4 star and has no lead in it with which to protect the valve seats. This leads to what is called "Valve Seat Recession" which is the physical burning away of the valve seat caused by excessive heat. This, in turn causes the valve clearances, or tappet settings, to close up, which will then eventually not allow the valves to shut properly. This will cause the edge of the valves to burn away and this will then lead to poor compression and engine failure.

The second problem is that the Octane rating of unleaded petrol is less than that of 4 star, which has an Octane rating of approximately 98, whereas unleaded only has an Octane rating of 95. This can lead to detonation, or 'pinking', which is a result of the fuel being ignited too soon in the cylinder. The sound of the pinking is, in fact, the fuel exploding violently in the cylinder rather than burning rapidly in a controlled flame spread. This violent explosion can cause major engine damage and, in extreme cases, hole a piston.

So, these are the problems associated with the use of unleaded petrol in leaded engines and, on the face of it, sounds quite frightening and the outlook seems quite bleak. However, the Technical Department at Ford, have provided some encouraging information.

If unleaded petrol is to to be used in a Capri, the problem of pinking must be overcome, and this is done by retarding the ignition timing as follows;

1300cc Kent engines Retard from 6 to 2°

1600cc Kent engines Retard from 6 to 2°

Early 1600 OHC Retard from 6 to 2°

VV carb 1600 OHC Retard from 12 to 8°

2 litre OHC Retard from 8 to 4°

2.8 Injection Retard from 12 to 9°

3 litre Essex Retard from 14 to 10°

From around 1986, Ford started to fit hardened valve seats to a lot of their engines, and from 1989 all Ford engines were equipped with 'Hard Heads'. It is possible that some of these found their way into some of the very last Capris. These hard heads have certain markings on them for identification.

The 1600 OHC with hardened valve seats will have either an 'M', 'MM', 'N', on 'NN' stamped on the exhaust flange adjacent to number 4 spark plug hole. The 2 litre OHC will either have a 'P', 'PP', 'R' or 'RR' stamped in the same place and the 2.8 Injection will have a 'D' or an 'E' stamped on the exhaust flange. The 3 litre Essex or 1300 and 1600 Kent engines were never built with Hard heads, but the Valencia engine as used in the Fiesta and Escort is very similar to the Kent, and these engines are still used today.

So, what do you do about this unleaded petrol? If your Capri has any of these markings, all you have to do to run continually on unleaded petrol is to retard the timing to stop the detonation and the problem is all but solved, apart from the slight loss of performance you will encounter as a result. You could source the cylinder head from a new Ford, which does have the hard head markings and fit it to your Capri. If you own a 3 litre Capri, you could have hardened valve seats fitted to your existing cylinder heads (as you could with any Capri engine), and this would also solve the problem, apart from necessary timing adjustment that will be required. It has been reported, however, that under certain circumstances some valve seat inserts have fallen out into the combustion chamber while the engine has been running, which resulted in engine destruction!

There does seem to be a very easy, relatively cheap and simple solution to this problem, in the form of a Catalyst that is simply added to the fuel tank. There are two companies marketing similar products, both of which have been running advertisements in the car magazines. One is called 'Broquet Fuel catalyst', and is marketed by David Lock and Associates, and the other is called 'The Fuel Cat', and is marketed by a company of the same name.

They both claim to allow a 'Lead only' engine to run continuously on unleaded petrol without the risk of engine damage and without having to retard the ignition timing. Sounds too good to be true, I hear you say. I too was filled with scepticism, so I contacted both companies to obtain further information.

It would appear that it was developed during the Second World War to allow Hurricane aircraft, on loan to the Russians, to run on the very poor quality fuel they had at the time, and this it did very successfully. More recently, it has been used by the Civil Service Motoring Association since 1989, and collectively their members have covered in excess of 200 million miles using Broquet with no reports of any engine damage from any of their 10,000 members.

Basically, it consists of a mesh bag filled with predominantly tin pellets, which is simply dropped into the fuel tank. This causes a catalytic reaction which causes it to change the properties of the fuel, resulting in much more efficient burning, and this in turn means that the combustion temperature is significantly lowered to below a safe level for 'Lead only' engines to operate. This more efficient burning also gives improved fuel economy, more power and less carbon build up in the cylinders, so a cleaner engine. Broquet also offer an 'Engine Damage Warranty' that states that if an engine is damaged by the use of their product, it will be repaired or replaced at their cost.

You can contact  at:

Broquet International Limited
56, Percival Road,
CV22 5JT,
United Kingdom

Tel:  +44 (0)1788 540068
E-mail: info@broquet.com

Next I wrote to Fuel Cat, and was then contacted by Phillip Brodie, who is the Managing Director of Fuel Cat, the company, who was very helpful. His product is fundamentally the same as the Broquet and it has been on sale since 1991, and again has had no reports of any engine that has been damaged by the use of his product and unleaded petrol. In fact, their information pack states that 'the use of Fuel Cat in auto and marine engines is wholly beneficial and cannot in any way prove harmful to an engine or its fuel system'. Fuel Cat can be contacted at:

100 Goldsmith Avenue
W3 6HW,

or you can phone on +44 (0)208 896 9172

These are facts concerning unleaded and our beloved Capri. I'm sure that now 4 star has disappeared from pumps there will be an approved additive that can be poured into the tank when you fill up, as indeed there is in Europe, but this may prove to be an expensive option in the long run. Having your engine modified with hardened valve seats would appear to be the safest option, but again this would definitely prove expensive and not without its problems. So, in conclusion, after looking at all the facts, it would appear that the cheapest and, indeed, the easiest option, is one of the fuel catalysts. It is a once-only fitment and both companies offer excellent engine warranties. It appears to solve all the problems in one foul swoop, but as I personally haven't used either product myself, I can only pass on to you what the two companies, claim as being 'The Facts'. Contact them today and see for yourself what they have to say.

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