Yup, another octane thread.
Melting Slicks
Joined: Aug 2016
Posts: 2,762
Likes: 1,017
From: MOUNTAIN HOME Arkansas
After some Google research, just couple of minutes, I found RON stands for Research Octane Number, MON is Motor Octane Number. Short answer 2 different ways of measuring octane thru similar test engines but with slightly different parameters (engine speed/preheated fuel/variable ignition timing). Couldn't even find the 91+Oct explanation but assume (ugh-oh) it just means 91 or more(?). Anyhow, just put what the OM says to use (LT1 versus LT4). There is the OCD way of doing 50/50 or 60/40 mix of different Octanes of fuel to get what you need/want, but seriously? Our cars computers can adjust for a wide range of fuel without tunes but I would err on the slightly high side if no other choice. There is agreement by most companies that is possible to damage the cats using higher than recommended Octane because some fuel is not burned in the engine & burns when entering the Cats. I suppose that is why tunes are done to run Meth or higher Ethanol blends for track/racing. JMHO
Last edited by madrob2020; Jan 20, 2018 at 12:09 PM.
Le Mans Master
Joined: May 2000
Posts: 8,729
Likes: 1,508
From: Redmond WA
Yah. We Americans are a simple people and cannot be confused with TWO octane numbers, so they average them for us. Problem is when you actually need 92 RON but you've some low RON averaged with some high MON. It averages out to 92 but still detonates... just a contrived example.
Thread Starter
Racer
Joined: Nov 2017
Posts: 473
Likes: 89
From: Yorba Linda CA
After some Google research, just couple of minutes, I found RON stands for Research Octane Number, MON is Motor Octane Number. Short answer 2 different ways of measuring octane thru similar test engines but with slightly different parameters (engine speed/preheated fuel/variable ignition timing). Couldn't even find the 91+Oct explanation but assume (ugh-oh) it just means 91 or more(?). Anyhow, just put what the OM says to use (LT1 versus LT4). There is the OCD way of doing 50/50 or 60/40 mix of different Octanes of fuel to get what you need/want, but seriously? Our cars computers can adjust for a wide range of fuel without tunes but I would err on the slightly high side if no other choice. There is agreement by most companies that is possible to damage the cats using higher than recommended Octane because some fuel is not burned in the engine & burns when entering the Cats. I suppose that is why tunes are done to run Meth or higher Ethanol blends for track/racing. JMHO
I was merely pointing out the irony of a sticker that, at the same time suggests minimum 91 octane while also directing the driver to the owners manual (which we’ve all seen in 900 posts recommends 93 octane). I made the California comment as an aside in case anyone thought the 91 octane sticker might be a California-specific decal.
Last edited by MacRoadie; Jan 20, 2018 at 05:44 PM.
