Q: What is the best fuel to use? A: It is officially recommended to use a minimum of Super Unleaded (97 RON) in all Evolution models in the UK. The Evolutions are built for the Japanese home market and as such the cars would normally use 100 RON fuel or greater. The engine management in the Evolutions can adapt to lower octane fuels but performance will be reduced to prevent detonation. The higher the octane fuel you use the less chance detonation will occur allowing better performance. Shell Optimax is currently the highest RON rated readily available pump fuel in the UK (guaranteed at 98 RON but typically 98.6 RON) and using it should improve performance slightly over normal Super Unleaded. It has also been proven that Optimax is extremely good at keeping the engine clean of combustion by-products. It is not recommended to use ‘supermarket’ brand Super Unleaded as these have less detergents or cleaning agents than major brand fuels and can lead to coking of the valves. As for 95 RON Premium Unleaded the official advice is do not use it unless in an emergency. If you have to fill up with 95 RON Unleaded for any reason then drive carefully until you get a chance to fill up with a Super grade unleaded again. It is also officially recommended that Octane Boosters are not used, even in an emergency. It has been suggested that driving for long periods on 95 RON Unleaded can possibly lead to damage of the engine however, Evos are run in countries without major problems where the maximum rating of fuel available is only 93 RON (e.g. Greece, China and the West Indies). If you have to or want to run on a lower RON rated fuel then it may be wise to reprogram the engine ECU to suit low Octane rated fuel or fit an aftermarket ECU system or ignition controller (basically retard the ignition map slightly to prevent detonation). Do not use 4 Star or Lead Replacement Petrol, it may have a higher Octane Rating but it contains additives that can damage the Catalytic Converter and the Oxygen sensor. Back to question page