- 89,833
- Rule 12
- GTP_Famine
syclone538Our octane is rated (research + motor / 2). Research octane number is tested with a lower rpm and lower intake air temperature then motor octane number so 98 RON is lower when measured in MON (just a guess but I would say about 85 MON). If you want a more specific explanation I can look it up. My truck has 8.3-1 compression and runs 14.7 psi (1 bar) of boost with about a 130* intake temp under boost and I have no knock/detonation with 93 R+M/2 octane gas.
98RON ("Super-unleaded"), if it had an MON of 85, would have a PON of 91.5. 95RON, assuming a similar percentage difference (although intuitively it'd be slightly lower, so a higher number) would have a MON of 82, for a PON of 88.5.
I'm not surprised you have no knock with 93 PON - expert advice is to use the lowest octane rating that gives you no knock, and you're using the highest PON available for road cars. The question is would you get any knock with lower octane ratings? Try your 91 for a couple of tanks.