I'm in NorCal, the 91 Supreme at Chevron (and everywhere else) is just fine and I drive a lot at full throttle. On my previous 987 Boxster S of 12 years, for economy I often alternated with the cheaper middle-grade Plus (89?) and never encountered knocking. Same with our other German cars which recommend 93.My 718 owner's manual specifies 93 octane gas, but it's been years since I saw anything more than 91 octane here in California. What do you all do? Just use 91 and hope you don't experience light detonation at full throttle?
Ah, that explains it. Thanks. I don't discern any difference between 95 and 98 but it is apparently better for your engine wear and tear. I did notice a huge difference with 100 RON in Germany. Like aviation fuel on performance and sound, throttle blips in standard mode. But I reckon the mpg wasn't very good - unless that was because I was encouraged to more spirited driving.The UK and Australia (at least) use the straight RON method for rating octane. The USA (and others) use (RON+MON)/2.
There is not a direct relation between RON and MON. (Wikipedia has details.)
I assume the different countries have different manuals and different stickers inside the fuel inlet cover.
Maybe yes and maybe no. There have been tests of fuel here that show some fuels are actually under rated and others over rated.There's a place in Sunol that has race gas, but otherwise yeah it's 91 here in Cali. I have to assume that's ok. On my nice cars I've ONLY put Chevron in for the longest time because I heard at some point that Techron actually works well, and was a competitive advantage over other companies, but that could be all BS these days.
So are you saying with certainty that the 100 octane Shell 'Racing' is actually a leaded fuel or at least partially leaded and, thus, will damage the cat converter and/or other engine parts? If so, this is good to know, thanks. It definitely made my 981 basic boxster go like an S and throttle blip even without being in sport mode. But with poor mpg consumption. Haven't tried it in the 718S and now definitely won't!Octane is a measure of how much compression the fuel can take before it detonates.
Lower octane than 'useable' used to cause detonation or "pinging" which was bad. That means the fuel ignited irregularly rather than burning predictably, timing was changed, and cylinder pressures could skyrocket.
With the advent of highly computerised engine management units a slightly lower octane is usually no issue as the computer can "de-tune" the engine slightly to compensate.
All other things (fuel composition, additives, etc.) being equal, an octane rating higher than needed would not change engine performance, and is a waste of money. Of course very high octane car fuels often have alcohols or octane boosters added which change the composition. They may also clean out cylinder/piston deposits and that can change performance.
With leaded fuels the engine performance could be confirmed by the colour of the carbon deposits in the tail pipe. Unleaded and computers mean that this is no longer useful.
Avgas at 100 octane+ or racing gas should not be used in engines designed for unleaded fuels as they contain lead to increase the octane rating and significant damage can occur with significant use.