High Octane Fuel

[bondms]

There have been numerous postings on this site claiming that higher octane fuels (in particular Shell Optimax) give improved performance and/or better fuel economy.

I understand that higher octane fuel is used by racing cars because it allows the use of engines with higher compression ratios which gives a more efficient burn (translating to more power and/or better economy).

However, when you use a higher octane fuel in an engine designed to work with standard fuel then the compression ratio is unchanged so where does the extra power and/or economy come from?

I guess it's something to do with the ECU advancing the spark timing. I know that most modern engines have a knock sensor which can allow the ECU to detect the optimal time to ignite the mixture but I don't understand why an advanced ignition with higher octane fuel is better than a retarded ignition with a lower octane fuel. Can anyone please explain this?

Cheers.

[aido]

Haven't got a clue really but I think I read somewhere that a lot of Jap cars are designed to run on 100RON so basically you're cripping them by feeding them 95RON and as soon as you give them something a bit richer they realise this and start to perform more like they should.

If we lived in Holland you could get V-Power which is 100RON out of the pump (think that's right there was one country selling V-Power as Super from what I remember).

Does that sound about right guys?

Know with the charger fitted the fueling is running flat out and from what I've read on here it's best to stick to Optimax or equivalent (guess that leaves me with just Optimax then!)