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  1. #1
    JACoolTA's Avatar
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    91 Octane in FX SHO?

    I know that the FX SHO is "tuned" for 87 octane, but we have fuel tanks at our plant and we have high octane in them. I hate having to go to town just to fill up the skis, when I have fuel right there at our plant. Do you think there is anyway possible that running higher octane would hurt performance?


  2. #2

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    Running premium in a motor that doesn't require it is not a good thing!!! It will not kill the motor but someone will chime in with the reason. I have never used more than the required octane in any of my motors.
    Last edited by roost5o; 08-15-2008 at 10:06 PM.

  3. #3
    BarBayBULL BAR BAY H.O.'s Avatar
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    The way I understand it, 91 will not hurt or help an engine tuned for 87. It should burn cleaner but you will not see any difference in performance. Most say it is a waste of money.

  4. #4
    JACoolTA's Avatar
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    That is exactly how I see it. I am not looking to gain anything. Like you said though, it will burn cleaner, which is a good thing for a engine. I know that with my cars and trucks that I have performance computers on, you have to run a higher octane to prevent "spark knock". I have heard that the programming of the computers leans the engine out more to gain power and running a higher octane is a must though. I just did not know how finicky these new jet skis may be. I know that in my 4 wheelers I have always ran high octane fuel with no problems. The plugs always look normal too.

  5. #5
    Hardcore's Avatar
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    Higher octane fuel is not "cleaner" , the higher octane rating means it has less energy and takes more heat and compression to explode or burn. The reason being so when the piston is traveling up the cylinder on a higher compression or high boosted motor, the residual fuel, or freshly spraying fuel in the cylinder doesnt start to burn too early, because of either a hot cylinder or due to too much ignition advance. If the fuel starts igniting too early it causes the piston to fight is way up which can cause all types of trouble, the least of which is making the pistons rock back and forth on the wrist pin (knock) and galling them or the cylinder, or breaking off a piece of skirt. It is possible to lose a little power running too high of an octane but the reward of not having the extra safety leg of high octane in a performance motor is not worth it IMO, especially a motor that stays at a constant hig RPM load for so long.

  6. #6
    Quote Originally Posted by Hardcore View Post
    Higher octane fuel is not "cleaner" , the higher octane rating means it has less energy and takes more heat and compression to explode or burn. The reason being so when the piston is traveling up the cylinder on a higher compression or high boosted motor, the residual fuel, or freshly spraying fuel in the cylinder doesnt start to burn too early, because of either a hot cylinder or due to too much ignition advance. If the fuel starts igniting too early it causes the piston to fight is way up which can cause all types of trouble, the least of which is making the pistons rock back and forth on the wrist pin (knock) and galling them or the cylinder, or breaking off a piece of skirt. It is possible to lose a little power running too high of an octane but the reward of not having the extra safety leg of high octane in a performance motor is not worth it IMO, especially a motor that stays at a constant hig RPM load for so long.
    This is a good explanation. That being said, you are giving up performance using the higher octane in a stock motor as the 87 has more "bang" for the buck. In the 2 stroke modded GPR's we're getting a good increase in top end rpm's using lower octanes so their is a definite difference in how they burn. The 87 octane has more "punch" as it ignites faster, just don't use it if you turn up the boost or increase the compression.

  7. #7

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    ^^^^^^What he said!!

  8. #8
    Since higher octane fuel burns slower, you need the high compression to burn it all. With lower compression engines, the fuel won't burn completely and will leave carbon on your head. Eventually, you will need to have the head removed and the carbon removed from it and the valves.

  9. #9
    tiffy's Avatar
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    Well I have a stock 04 FX Cruiser. I had half a tank of 87 ocatne fuel. My Dad flies planes and took some AVGAS out which is 100 octane. He filled half of my tank with it making it about 98 octane. I noticed no gain or loss.

  10. #10
    amharms's Avatar
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    Probably the only benefit to premium in a SHO is ethanol avoidance...

    I'm thinking about switching to premium soon so I can get the ethanol out of the tank before it has to sit for the winter...

    edit: unless, of course, someone knows of a gas station in Plano, TX that sells ethanol-free 87

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