You don't 'have' to use it, but 97/98 RON burns quicker than 95 RON, hence you can burn more petrol in the same amount of time, more petrol=more power.
I assume the squadra chip sets things up to utilise this quicker burn rate and thus produce more power.
I think, someone who knows will prolly tell us the real reason
Because, the remap moves some of the injection timings and the fuel mix ratios, it requires that there be more control over the ignition process. Higher octane = more resistance to explosion, and more controlled burning.
Explosion = detonation = damage to engine/pistons...
I would have thought similarly, but it seems that it's all to do with compression and having a volitile mix of fuel enclosed in such a small space.
More refined control over the process is required.
The higher the octane the lower the tendency to combust/detonate.
Higher octane fuels will generally yield greater power as they can be used at higher compression ratios. Lower octane fuels will tend to pre-ignite during the compression phase of the 4-stroke cycle (a phenomenon known as knock) partly by the charge being compressed past it's detonation point and also by the ignition advance. The ECU has sonic knock sensors on the block that detect when pre-ignition is taking place and winds back the ignition advance to prevent it happening, I believe it also changes the mixture ratio too.
Basically if your engine is tuned to use 98ron fuel, if 95ron is used then it will pre-ignite and knock then the ECU will change the ignition advance and fuel/air ratio (burn more lean) to prevent it.
To understand why knock can damage an engine, imagine that normally the pressure of the charge reaches a maximum when the piston is nominally past TDC and just about to move downwards, in a knock condition maximum pressure is attained prior to TDC and starts trying to push the piston down as it is still rising. This causes immense strain on the con-rods, head seal etc.
Cheers McGuinn and Phade
Does this mean that the advantage of using higher RON is that more fuel/air mixture can be drawn in the barrel? I'm assuming the volume in the barrel is constant at TDC so the only way to utilise the higher compression is to fill it with more mixture. Or is the mixture just richer?