Fuel mix: Leaded AND Unleaded

[Stuart]

exactly, ron is merely the fuels resistance to pre ignition... the calorific value is "usually" lower so if you dont change your ign settings it will lose you power and thermal efficiency from less engery transfer and also with a slower burn due to its ron "could" result in even more lost power as the peak cylinder pressue maybe pushed past the best point for torque... and keeping heat so late in the cycle can burn valves out.

but thats all theory and my personal views... which lets face it are cRaZy lmao

[Jack]

^ Thats pretty much summed up what I've learnt today :D

Also picked up some interesting info about Tesco 99RON; whilst the company who supply the fuel bang on about it having high RON/MON, they don't mention the calorific value. But they do say:

We also typically include 5% bioethanol ? a clean and pure ultra high-octane component which is also renewable to help cut greenhouse gas emissions.

They don't however mention that 5% ethanol is more than likely what raises the RON to 99; and also fail to mention adding ethanol lowers the calorific value of the fuel, so putting it in your average European car (tuned for either 95 or 97RON) which doesn't advance/retard the timing enough to make use of the higher octane could cause it to lose power.

Anywho, rambling and somewhat off topic now

[Stuart]

have to say my vx and an M3 i know of both respond better to tesco 99ron than on any other "fancy fuel", and when i say respond better they pic up revs better but power is about the same as usual...... i guess it ccould lead to better mpg, but as with all nice things you deck it more so its a vicious circle lmao