RON Octane Gasoline rating

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The 1966 Mustang owners manual says that the fuel should be 91 RON octane "Regular" fuel for the 2V carburetor and 99 RON octane "Premium" fuel for the 4V. About what are those ratings using today's R+M calculations? I know that the "Motor" rating is lower than the RON, so I am thinking that any 87 or 89 is probably good for the 2V but how about that 99 RON, what pump octane would that be now? Thanks
 
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99 RON would be approximately 93 AKI (R+M)/2, the current measurement here in the US. I've never seen a pump label distinguish between RON and MON, only the average. It's as close as you will get here in the US without buying specialty (race) gasoline or leaded aviation fuel.
 
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Originally Posted by kschachn
99 RON would be approximately 93 AKI (R+M)/2, the current measurement here in the US. I've never seen a pump label distinguish between RON and MON, only the average. It's as close as you will get here in the US without buying specialty (race) gasoline or leaded aviation fuel.
The scales that are out there are imprecise rules of thumb. Pure iso-octane of course has a RON of 100 and a MON of 100. But in general it's close enough with most pump fuel to have a RON then an AKI octane recommendation.
 
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Originally Posted by thastinger
Research Octane numbers are generally on the order of 10% higher than Motor Octane numbers. This might give you an idea https://vpracingfuels.com/master-fuel-tables/ but I would think the fuel you're trying to buy would have the RON and MON posted somewhere on the website
The only requirement when sold in the US is the (R+M)/2 rating. It is possible to have a different "spread", and of course there can be different fuels with different spreads being mixed into the same storage tank. They should average out to the same AKI.
 
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I've heard Research is 4 points higher than (R+M)/2. Naturally the 4 bbl carb has a more aggressive (compression, cam, timing) engine sitting underneath it than the 2V-- carburetion is only incidental.
 
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looking at the benefits of oxygenated fuels is interesting, kinda why NITRO an oxygen bearing fuel can be burned at such high volumes making OUTRAGEOUS power in top fuel drag racing
 
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Difference between RON, MON, and AKI Because of the 8 to 12 octane number difference between RON and MON noted above, the AKI shown in Canada and the United States is 4 to 6 octane numbers lower than elsewhere in the world for the same fuel. This difference between RON and MON is known as the fuel's Sensitivity,[5] and is not typically published for those countries that use the Anti-Knock Index labelling system.
 
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130
Location
Michigan
Thread starter
Thanks for your inputs. As was noted in one post, only the average of R+M is shown on the US gasoline pumps. I did click on the master fuel table link and found that the differences between R and M were from 3 to 15, so quite large differences. Maybe the best thing to do is to experiment. i think I will try the lowest octane and work up until I don't hear and knock/pinging going up hills. Start with 87 for the 2V and 90 for the 4V.
 
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