I’ve heard the ”Performance number” before but as often Ive also heard octane numbers above 100
As I said, for ratings above 100 the community has adopted the word "Octane", but technically it's not correct. Octane rating of a fuel is one that has the same knock characteristics of a particular mixture of iso-octane and heptane. 90% iso-octane and 10% heptane has an octane rating of 90. Pure iso-octane ie 100%, has a rating of 100 octane. With a fuel that has better knock characteristics than 100% iso-octane they obviously had to come up with a means of quantifying the knock rating, hence the "Performance Number". As you can see from the chart both lean and rich ratings are given as PN ("Performance Number") because both are above 100, though they seem to have transposed the rich and lean numbers. Once again, technically 100 is as high as an octane rating can go. I must emphasise the word technically ie the petroleum industry, not community common usage.
