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Join Date: Jun 2006
Location: Corpus Christi, Texas
The bike is designed to run on 87 octane fuel. Octane rating is a vastly misunderstood topic. Higher octane does NOT equal better performance. Octane simply measures a fuels resistance to preignition (knocking). The higher the octane, the better its preignition resistance. Higher octane fuel actually burns cooler because of this. The only reason to run the higher octane fuel is if you have a high, 12:1 or better, compression ratio. Our bikes are at about 10:1 so 87 works just fine.
The higher octane fuels also contain a lot of detergents to clean the intake and exhaust systems. If you run a higher octane than recommended, the lower burning temperature of the gas creates residue in the exhaust system that the detergents can't get rid of because the fuel isn't being burned efficiently. It can lead to a gunked up exhaust system though your intake will be squeaky clean. Stick with 87.
Some of the confusion comes from the owners manual where it says to use either 91 or 87. This is because different countries use different methods to arrive at octane ratings. We use R+M/2. This is where the 87 comes from. Other places only use the R value and this is the 91. In the US we use the R+M/2 so again, stick with 87.
93 VN 750 "Ursula"
Moved R/R 08Sep06
R/R rewire 17Feb07
New R/R, Installed 14Jun08
New Stator installed 10 Jun08
Maintenance Free Battery 12Jan08
Last edited by Sky Rider; 08-09-2008 at 11:14 PM.