My manual says to run 91 or greater octane, so I've religiously run 93 octane Texaco gas. Recently I was low on gas and there were no gas stations around other than a 76 and they only had 91 octane fuel. After filling up I noticed that my motorcycle was running significantly smoother. There are no longer any sudden drops in rpm, and my engine rpm stays even throughout the powerband.

Is it smoother because I'm using closer to the recommended octane? Or is this because of the quality of the gas? I had always assumed that using a higher octane wouldn't have a noticeable difference in performance, but it sure did (for the worse).

Motorcycle: 2017 Yamaha R6 (Factory recommended minimum octane is 91)

Weather/Temperature: Hot and humid

Elevation: Sea level

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    While this is STRICTLY my opinion, I've had nothing but sucky experiences with Texaco gasoline. After two or three times (different gas stations) where I got water in my fuel, I quit going there. My suggestion to you is, if the 76 is running better, use it. I cannot believe all Texaco gas stations have bad fuel. If something is working for you, why go back to the old? – Pᴀᴜʟsᴛᴇʀ2 May 19 '18 at 0:28
  • That's true. I was still hoping for an explanation. After your sucky experiences with Texaco, which gas did you decide was best? It seems like all Texaco stations had the same performance 'issues'. – Mocking May 19 '18 at 0:37
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    It has definitely changed throughout the years. I now use Costco gas for two reasons. One it's usually cheaper. Second it's "Top Tier" gasoline. I've found it works really well for my cars. Really, find something which works for you and stick with it ... even the gas station you use. – Pᴀᴜʟsᴛᴇʀ2 May 19 '18 at 1:46
  • Some people have strong negative and positive feelings about Costco gas. My dad is one of the people who thinks it ruins your engine. I'm sure that's an exaggeration. If Texaco has had issues with water in their gas, I'm not sure top tier really means anything. Guess I'll try Costco later. – Mocking May 19 '18 at 3:52
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    Lower octane will cause the engine computer to reduce timing advance with could cause a smoother running with some loss of performance. All top tier means is they have detergent additives that non top tier do not. – Moab May 20 '18 at 19:19

Lower octane will cause the engine computer to reduce timing advance with could cause a smoother running with some loss of performance. All top tier means is they have detergent additives that non top tier do not.

  • Really? What does the computer use to sense the type of fuel or the affect it's having in order to make its adjustments? – raydowe May 29 '18 at 11:56
  • It doesn't have anything to do with it, lower octane fuel burns slightly faster and can cause different idle and running characteristics. – Moab May 29 '18 at 14:30

One thing to consider would be to buy the gas that will be consumed in the shortest amount of time by customers.

If you purchased 93 octane (which probably means (RON+MON)/2, i.e. about 98 RON), this is a premium gas that most customers won't purchase due to its price. The turnover for the gas is low, and therefore, you get relatively old gas.

If you purchased 91 octane (which probably means (RON+MON)/2, i.e. about 96 RON), this is a gas that more customers will purchase than the 93 octane. For this gas, the turnover will be higher, and therefore, you get somewhat more recent gas than for 93.

My advice is simple: get the lowest recommended octane number within certain sane limits. Not only you save money, but also the gas will be more recent due to higher turnover.

For this reason, I choose 95 RON (with at most 10% ethanol) for my car. There is a 98 RON (with at most 5% ethanol) here for more picky cars, but many storage facilities were installed when there was a mass hysteria about the ethanol content of 95 RON (high temporary demand for 98 RON and large 98 RON storage facilities in the fuel stations), and now the mass hysteria seems to have ended, meaning the turnover is very low for the size of the 98 RON storage facilities.

Selecting where you refuel will also help. I always refuel at Neste (I'm in Finland), because I believe their gas has higher quality.

  • Here in the States, when you purchase 91 octane fuel, the pump mixes the 89 and 93 as it dispenses to get the 91. Most fueling stations only carry 89/93 in their tanks. This means the 93 gets used up right along side the 89, albeit not as fast, but it does get circulated. Your point is well taken about going to busy fueling stations, though. Busy stations usually carry fresh gas. – Pᴀᴜʟsᴛᴇʀ2 May 19 '18 at 13:09
  • 91 was actually the highest octane available (premium) at the station I went to. But yes, point taken. – Mocking May 21 '18 at 19:29

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