No difference whatsoever. Some cars are designed to run on 98 super, mainly quick/new cars. 98 can be a necessity on some older turbo motors if theyve been modded to run higher boost and the extra octane will enable them to run this sort of boost without detonation problems. Essentially, any car that is supposed to run on Super, has to be run on Super otherwise once you start to cane it, it will at best be sluggish and at worst youll knacker the engine (depending on how comprehensive the engine management is).
A car that is designed to run on 95 RON normal unleaded does not need to use 98 RON at all. Many people may feel happy thinking that they are treating their car to a pampered existence feeding it Super when it doesnt need it, but it really makes no difference at all, the car is not designed to use super so it will not advance its timing to use the extra octane, therefore no more power, no more fuel economy. Youre paying extra for basically a few fancy detergents. All petrol has detergents in it anyway. Maybe Shells are better, I dont know but no-ones engine ever knackered up from using Tescos normal unleaded all its life.
Injectors occasionally clog, thats just life, whip em out and get them serviced at a Bosch centre. If running Optimax all the time stops this then great, but its such a minor problem thats its not worth paying for Optimax all the time unless your engine requrires 98. A bit like when you buy a washing machine and they try and get you to pay another £150 for a 5 year warranty which you really dont need - if it ever breaks down itll cost less than that to fix it anyway, or itll be so old by then that youll be getting rid of it.
and super unleaded is 78.5p
