Anyone tried Shell Optimax Unleaded in their ? Any benefits? I have tried it in my Mini Cooper and it made a small difference, possibly psychological?

Slightly more resposive at lower revs.

I think it makes a difference over 95 rated fuel but not so much over 98 (optimax is 100). I use BP/Aral's Ultimate petrol all the time and nothing else. It also has additives in the fuel which apparently is better for the engine nd helps keep it clean and in optimum condition (no doubt manufacturer waffle but it might be true )

I've started to use the premium fuel's, BP ultimate if possible, and it has made a bit of a difference. I try an aviod the crappy mixed fuels in supermarkets now.

I used optimax when my st was standered n didn't notice any differance in optimax or normal juice. But then i installed bluefin stage 2,had a milltek zaust,decat n flexi..... N boy can you notice the differance between the 2 now...... OPTIMAX ALL THE WAY!!!

The Optimax and other performance fuels have two key differences to standard fuels:

• The RON (Research Octane Number, usualy 95 for standard UK fuel, higher for performance fuels)
  
• The fuel additives

The octane number of fuel essentially grades its resistance to premature detonation, the lower the octane number the higher the chance of pre-ignition. This is when the fuel/air mixture ignites before the optimum timing. This will result in a loss of engine performance and can lead to a knocking sound from the engine, known as engine knock.
The Duratec engine can comfortably run on 95RON fuel, some performance engines require higher octane ratings as they have higher compression ratios. The duratec engine in the ST does have an active knock sensor so that the onset of knock (premature detonation) can be detected and fuel/air ratios changed and spark timings differed. This is all controlled by the ECU and you won't even notice it as you drive along. The advantage that the higher RON number bring to the ST is that as knock is even less likely to occur, the timings should always be at an optimum, this will result in better performance, although only to a very small extent.

Additives can be mixed with fuel to improve its properties, different additives will be added to achieve different results. Probably the best know fuel additive was tetra-ethyl lead, this improved fuels knocking resistance, but was environmentally unfriendly so was phased out. The reason it was not imediately removed was that many engines used the leads secondary function, which was to protect the valve seat from corrosion, so some vehicles had to be modified. Lead is still used in aviation fuel for light aircraft, and some engines still require lead fuel to run. There are additives in all fuels that improve its performance, these aditives normally focus on improving the stability and life of the fuel. The additives in the performance fuels that improve an engines performance are those that keep the internals of the engine clean by preventing carbon deposits, which can result in better engine performance, as well as more environmentaly friendly exhaust gases.

Sorry for the mini essay!

Maze are u working in Shell industry ??

lol

Nope, I just done loads on fuels for my degree. I got a little carried away with that reply!

Just a shame it costs a packet to buy the stuff. Pump price over here in germany for ultimate is around 1.45 euro a litre, so £1 in your money.

It's about the same over hear.

my st has been mapped on 97 ron fuels and i can definatley feel a difference when using standard fuel.... most notibly the lack of throttle response and appalling mpg

Do you reckon that using 100 octane over 95 will improve the 0-60 time and the in-gear acceleration times significantly? A test of the same car on each fuel would be cool.

marginally i suppose