[swrx2810]

Originally Posted by Scott.T

Just checked a copy of JDM, USDM and Prodrive PPP in an 06/07 STi .

Fuelling -
JDM : 9.8AFR
USDM : 10.94AFR
Prodrive UK PPP : 11.07AFR

Ignition Timing -
JDM : 26 Degree's with 9 Degree's of possible retardation (so can pull back to 17)
USDM : 21 Degree's with 7 Degree's of possible retardation (so can pull back to 14)
Prodrive UK PPP : 21 Degree's with 5 Degree's of possible retardation (so can pull back to 16)

All the above were read of the map at 5200rpm, load of approx. 2.8 (for reference)

So you can see that the JDM map runs more advance but runs considerably richer, which negates the advantage of running the higher advance. Horses for courses and several ways to skin it.
All have the ability to pull considerable timing, so all should be safe to run various grades of fuel. But for optimum performance you want it running the 'max' possible ignition advance, so the high RON the more chance you have of hitting that max figure.

Once you are at the max figure there is no gain from high octane, and it will only act as a safety net and prevent detonation cause by heat build-up i.e sustained high speed, high torque, slow rpm transitioning.

Thanks Scott. The highest we have in the UK is 98?