Fuel octane explained.

[IdahoMtnSpyder]

His explanation of why using an higher octane is not beneficial is good. That is pretty much agreed to by all on this forum. But he somewhat glosses over why you shouldn't use a lower octane. It is as he says, to prevent pre-detonation, or pinging. What he doesn't discuss is what causes pre-detonation. There are several different causes for pinging, but all of them are characteristics in the combustion chamber that stay hot enough to ignite the fuel mixture before the proper spark moment. Some can be things like sharp corners that don't cool down enough between firings.

What I contend is the Rotax engineers have done a d*** good job of designing the combustion chamber to prevent hot spots being present and causing pre-detonation. If you don't have a source to cause pre-detonation, then you don't need to have a pre-det preventative in place. Except the engine has been designed to make appropriate adjustments to ignition timing and fuel/air mixture to mitigate pinging, if the sensors detect it happening.

In the 9 years I have been on this forum there has not been a single post from an owner who has had engine damage caused by pinging from using 87 octane gasoline. My experience a few years ago showed my gas mileage was a touch better when using 87 octane vs 91 octane. Why? I can't explain it.

 

[UtahPete]

I'm not an engineer. I respect those that designed my RT and if they say that I should use 91 or higher octane, that's good enough for me. My Spyder is a toy for my pleasure. I could have bought a far less expensive little motorcycle if the cost of fuel was my main concern, or I could just ride my Honda PCX150 scooter which gets 100 mpg. Buying premium gas seems prudent and worthwhile to me. I keep a bottle of octane booster in my frunk just in case I ever end up at a gas station that does not sell the right octane that I need.

:agree:

 

[BLUEKNIGHT911]

His explanation of why using an higher octane is not beneficial is good. That is pretty much agreed to by all on this forum. But he somewhat glosses over why you shouldn't use a lower octane. It is as he says, to prevent pre-detonation, or pinging. What he doesn't discuss is what causes pre-detonation. There are several different causes for pinging, but all of them are characteristics in the combustion chamber that stay hot enough to ignite the fuel mixture before the proper spark moment. Some can be things like sharp corners that don't cool down enough between firings.

What I contend is the Rotax engineers have done a d*** good job of designing the combustion chamber to prevent hot spots being present and causing pre-detonation. If you don't have a source to cause pre-detonation, then you don't need to have a pre-det preventative in place. Except the engine has been designed to make appropriate adjustments to ignition timing and fuel/air mixture to mitigate pinging, if the sensors detect it happening.

In the 9 years I have been on this forum there has not been a single post from an owner who has had engine damage caused by pinging from using 87 octane gasoline. My experience a few years ago showed my gas mileage was a touch better when using 87 octane vs 91 octane. Why? I can't explain it.

IMS ....you get it, I get it ... and some folks won't EVER get it .... Thanks for the explanation ..... Mike :thumbup: