It's the difference between the Research Octane Number and Motor Octane Number.topcatproduction wrote: Interesting, so they are basically 4 clicks down- or is that offset by the different units used? What does the R and M stand for, and is any 1 more accurate than another or are they just different like farenheight, celcius, centegrade etc?
MON is a stricter test.
Bit like the difference in how hp used is quoted to either J607 or J1349 (about 4% difference).
But back to the OP's question:-
http://www.powerchipgroup.com/articles/PET0605.pdf
