[Nezil]

Originally Posted by PackPride85

95 and 98 RON in Europe are equivalent to 91 and 93 in the US.

No it's not... At least not necessarily.

Originally Posted by msmiljanic

But, I have a theory that the 93 AKI map is actually developed from a 98 RON standard gas that PTF gets in Europe. The US gas with a different makeup of detergents and ethanol could have a lower RON with a higher MON like 97/89 or 96/90 which still gives you a 93 AKI but does not meet the assumption of the map.

Sort of this... MON is more important than RON, particularly for high compression and forced induction engines. I believe US gas has a higher RON and lower MON than really needed, but still resulting in being within the spec for 91 AKI, which is probably based on 89 AKI base with 10% Ethanol added to bring up the octane (here in CA).

When Halim took a look at my logs last year, he said it looked like I was using 87 AKI fuel based on his experience, and I don't doubt it! What he probably meant was it looked like something less than 95 RON European fuel, based on where he lives, with that being the minimum.

US fuel also has a lot more sulphur in it as far as I know. I think I read somewhere that this is one of the major reasons why oil degrades quicker in the US than other parts of the world, and why BMW still uses LL01FE oil here, but LL04FE everywhere else in the world.

US fuel may be cheap, but it really really sucks.

The whole Shell vs others argument also doesn't hold water... Shell may have better additives, which might clean your engine better, but it almost certainly uses the same base stock fuel, and octane isn't affected. I'm not saying it isn't better fuel (though I doubt it really is), but it's not better from an octane perspective.

Like dubzz24 suggested, adding just enough E85 to suppress knock can work, if you have access to it, but you'll run into HPFP limitations quickly so you can't run that much.

What surprises me is that this isn't a more publicised issue... Where is the Jalopnik article about it?