Octane differences between the US, Europe and Japan
I’m writing this, because I’m sick of seeing posts about doing JDM swaps and asking about octane ratings. Reading Danny50’s article about petrol will help you understand this much better.
In general, if your JDM engine is 10.6:1 CR, USDM Type R has the same CR, there’s no magic fuel that’s overseas that will run that the JDM engines run on. People run 11:1 CR on 93 octane (DC5 USDM Type-S). Just look at a domestic car, the 1970 Chevelle SS 454 had a CR of 11.25:1 ran off pump gas. This would seem to be common sense, but I guess it isn’t.
America uses a Octane rating system different from Eurasia. The US rating system is run off of AKI or PON and Eurasia uses a RON rating system
RON(Research or Road Octane Number) That number is how well the fuel resists knock at a certain CR. This is lab tested with no variation except the CR. So if your fuel is 98 RON that means it’s 98% iso-octane and 2% n-heptane.
MON(Motor Octane Number)is the same test as RON but the intake and temp is higher, and it’s at a higher RPM. MON is a better rating for seeing how well a gas resists knock under load.
In Example
Motor Octane Test (MON) Research Octane Test (RON)
Inlet air temperature 148.9 C 65.6 C
Engine jacket temp 100 C 100 C
Engine RPM 900 600
MON’s rating will also usually be 6-10 points lower than RON.
AKI(anti-knock index) or PON(Pump Octane Rating) is the sum of the fuels RON and MON Rating divided by 2. That’s why you see (R+M)/2 on your petrol pump when you go to fill your car up.
So if a fuels RON is 98 and the MON is 88 and you divide that by 2 you get our gas rating
(R+M)/2 = (98+88)/2 = 93
98+88= 186
186/2 = 93
See how that works?
See how the Eurasian pump number isn’t much higher than the US’s?
Side note:
The reason you can still get a “bad batch” of fuel is because sometime the mix can have higher RON and lower MON, or vice versa. But because its always equaling the number at the pump, it can still be a bad mixture.
SniperX
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Posted 11/12/2008 5:50:30 PM
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