Why do GGR always advise the use of super-unleaded fuel?
Can my engine management system be modified to allow the use of premium unleaded?
What will we do when four star and super-unleaded are no longer available?
In Europe, there are three types of petrol generally available. Four star leaded, premium unleaded, and super unleaded. Recent changes in EEC legislation have prompted the introduction of a fourth, Lead Replacement Petrol (LRP). We will now try to briefly explain the differences between these different fuels, and the purpose for each one.
Lead was used in petrol to act as a lubricant for the valves, and it also has excellent anti knock, (or anti detonation) properties. Detonation will occur when the fuel ignites itself (without ignition by the spark plug), once certain temperatures and pressures are reached. High performance engines work at high temperature and pressure levels and resistance to detonation is essential to ensure good performance, and a lack of mechanical damage. The detonation resistance of a fuel is described by its octane rating; a higher octane rating denotes a higher level of knock resistance.
It has been found that the lead content of exhaust emissions is harmful to health, so legislation has called for the lead content of four star fuel to be reduced over the past few years. The result of this reduction has created a four star fuel that in performance terms, is only a shadow of its former self.
The removal of lead from petrol was brought about for a number or reasons. It can create harmful exhaust emissions, and if used on a Lambda sensor and catalytic converter equipped vehicle; it would render these items obsolete by coating their reactive surfaces. To allow an engine to use unleaded fuel, special harder materials must be used in the valve seats. As the lead additive in fuel was also used for its anti knock properties, premium unleaded was introduced as a replacement for the low octane fuels, used in lower performance engines. Eventually, a higher-octane version was produced, called Super unleaded. This fuel contained non-metallic additives to give the knock resistance properties originally provided by the lead used in four star fuel. This fuel was designed as a replacement for four star fuel, and from a performance perspective, is found to be better than the leaded fuel. When the Cosworth engine was conceived, it was designed with the necessary hard valve seats etc. that would be required by unleaded fuel. The initial models however were sold without catalytic converters, and four star fuel was specified. EEC legislation has dictated that leaded petrol will be banned from general sale from 1st January 2000. To cater for vehicles that cannot run on premium unleaded fuel, Lead Replacement Petrol will be made available. This should be a direct replacement for four star fuel, but will contain alternatives to lead to protect valve seats and raise octane levels. The additives used in LRP are different to those used in super unleaded, and this fuel should not be used by cars equipped with catalytic converters and lambda sensors.
As explained above, the valve seats used in the Cosworth engine are compatible with unleaded fuel, and the effectiveness of super-unleaded is greater than four star leaded. (We actually always ran our Group A Sierra Cosworths on super-unleaded fuel). The later (green top) 4x4 Sapphire and Escort Cosworths are designed to use premium unleaded, but we would not recommend this fuel if the performance potential of the car is to be fully exploited.
Can my engine management system be modified to allow the use of premium unleaded?
It is possible to retard the ignition timing of the engine for premium unleaded, but a Cosworth driver does not usually appreciate the drastic loss of performance! The loss of performance is due to a lowering in engine efficiency; this will also lead to an increase in fuel consumption.
What will we do when four star and super-unleaded are no longer available?
As explained above, when leaded fuel is phased out, Lead Replacement Petrol will be the available alternative. Our fuel suppliers have advised us that due to commercial pressures, super-unleaded fuel may also be phased out at some point. It has come to light that the non-metallic additives used to create this fuel also have harmful side effects. The opinion is that fuel companies will support the demand for this type of fuel if it is commercially viable.
PLEASE NOTE THAT THE ABOVE INFORMATION WAS CORRECT WHEN WRITTEN IN DECEMBER 1998. CHANGES MADE TO EEC OR NATIONAL LEGISLATION MAY AFFECT THIS
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