RON and MON - Fuel Debate.
I've been browsing through alot of posts lately trying to become more educated in the fuel differences in the US and Japan. There has been an ongoing debate about whether or not JDM motors will run correctly on US pump gas. So... so far, what I've gathered, is that JDM Subaru's are tuned from the factory to run on 98 RON fuel, RON being the research octane number measured under controlled conditions as its run through an engine. MON - motor octane number, is a more accurate calculation of how the fuel behaves under load. MON is typically 8-10 points lower than RON based on what I read.
Now, the US uses the formula (RON + MON)/2 to determine the pump octane rating. So a quick calculation for 98 RON would produce an approximate US octane rating of 93/94...
Other things I did not determine was if the fuel used in Japan vs the US is chemically different. Does Japanese fuel still contain trace amounts of lead? Lead is known to be help prevent knock, so is that enough of a difference alone?
I'm trying to determine, based on the information I provided, if a JDM motor would run well (without detonation) on US 93/94 octane fuel, and if not, why. Why would it be necessary to retune if the octane rating is very similar?
Discuss.
I've been browsing through alot of posts lately trying to become more educated in the fuel differences in the US and Japan. There has been an ongoing debate about whether or not JDM motors will run correctly on US pump gas. So... so far, what I've gathered, is that JDM Subaru's are tuned from the factory to run on 98 RON fuel, RON being the research octane number measured under controlled conditions as its run through an engine. MON - motor octane number, is a more accurate calculation of how the fuel behaves under load. MON is typically 8-10 points lower than RON based on what I read.
Now, the US uses the formula (RON + MON)/2 to determine the pump octane rating. So a quick calculation for 98 RON would produce an approximate US octane rating of 93/94...
Other things I did not determine was if the fuel used in Japan vs the US is chemically different. Does Japanese fuel still contain trace amounts of lead? Lead is known to be help prevent knock, so is that enough of a difference alone?
I'm trying to determine, based on the information I provided, if a JDM motor would run well (without detonation) on US 93/94 octane fuel, and if not, why. Why would it be necessary to retune if the octane rating is very similar?
Discuss.