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  1. #1
    absentx's Avatar
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    Lets talk about fuel octane!

    Okay...so I am driving home today here in Milwaukee, and all of the sudden, in the middle of town, at the least likely of gas stations, I see on their billboard:

    "110 octane racing fuel available here"

    And sure enough they have a racing fuel pump.

    So, I was wondering...Ever since I put the HSP 92 octane domes on my 1050 everyone has always said that 92 octane is bareeeeeeely good enough for those heads...Even HSP told me the higher octane the better. So I always put in at least 93 or higher.

    But actually I have never found anything higher than 93.. until now.

    Any advantage to using something like 110 in my fairly modest boat?

    Lets assume money isn't a factor here...I don't want "rational, money as a consideration responses"

    .....unless of course it will rip my engine to pieces..?


  2. #2
    800AMSOIL4U's Avatar
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    If you put too high of an octane in your craft that only needs a 93 and you use 110 it will actually slow down.

  3. #3
    Bing-A-Ding-Ding-Ding, Brrrrrap! Brrrrrrrrrap!!! Polaris_Nut#1's Avatar
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    We have too many lame additives here in Massachusetts. I always run the next octane higher to make up for it with my 2 strokes. You might try a 50/50 mix 93 and 110 = 101.5 We used to have Sunoco 94 but I can't even find that around here. Did they stop making it? I never use octane boosters either they scare me. I don't need to be replacing top ends cause of em. I may not be getting all I can out of my machine cause I run stock heads on all of them now and mid grade gas, but there are reliable and almost affordable.

  4. #4
    xenonx's Avatar
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    High Octane fuel allows you to run higher compression without detonation. Running smaller domes will increase compression and thereby giving you better acceleration. Running too high compression may limit the engines ability to rev out....at least on 2 strokes.

    Closed course racing is where you would want max acceleration off the line and from buoy to buoy. Supercourse/Endurance racing does not require you to run sky high compression ratios because you can still make good reliable power on top with moderate compression.

    Unless you are racing and possibly need the out of hole acceleration, I would run smaller domes to safely get you in the pump gas zone. High compression will wear out the bottom end bearings sooner not to mention create more heat and sacrafice longevity.

    Running too high of an octane will slow ignition and run cooler...not always a good thing when wanting to make max power. This is why a lot of people in watercraft racing mix race gas 50/50 with pump gas..not just to save money.

    Bottom line is, you just need enough fuel octane rating to avoid detonation. This will change with air/water/humidity. Higher heat will increase the potential for detonation so what you can get away with in the Winter time will probably be different in the Summer.

  5. #5

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    i know you wanna run the higher octane if you plan on rideing for more than a hour

  6. #6
    ph2ocraft's Avatar
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    Here's a conversion chart I did, so I didn't have to keep guessing or bring along a calculator.

  7. #7
    absentx's Avatar
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    cool, thanks guys.

  8. #8
    PolarisNut's Avatar
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    92 octane HSP domes on a 1050 are plenty fine on pump gas. I ran mine all last year with a "limited" CDI and tripple pipes for miles on end at WOT and never had a hit of deto on good fuel. I know I've seen guys run more compression on a 1050 and still run 93 pump fuel. I'd make sure you get it from a high volume station though, as some of the hick stations have 6mo old premium.

    And one thing to remember about "blending" race fuel....its not always correct to just add the two octane numbers together and divide by two. Its much easier to make "bad" gas good, than it is to make "good" gas great. 110+87 may actually yeild 98 octane, but 110+94 will not necessarily end up as 102. Most fuel is rated by the R+M/2 method, and its actually the "M"otor octane that is most important in resisting preignition/detonation. There is a good write up on this on VPs website. I think Unocal also had one on blending.

  9. #9
    ph2ocraft's Avatar
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    I guess I better state my chart is VP110 leaded and Unical 91, which when sampled (a few ratios) turned out correct.

    I also ran pump gas in my SLTX with a limited CDI and triples at WOT you're right it will hold up with enough fuel delivery.

    Now take the same scenario, add a passenger and cruise around at 3/4 throttle, see you at the engine builders........

    One tank of crap, old, watered etc. fuel from the pumps and you again have the same scenario, why would you risk an engine for a couple dollars of better gas??

  10. #10
    TRIPLE PIPES ARE 2-STROKE TURBOS allcool's Avatar
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    A big advantage in 2-strokes from running/mixing race fuel with pump gas is the extra upper cylinder lubrication you get from the lead in 110 octane race fuel. In 4-strokes the valve seats/valves and guides love lead.

    I know for sanctioned ijsba events you must use unleaded race fuel now, but last time I checked the max octane of unleaded race fuel only is 103.
    So all the 110 octane fuels you see will have lead

    Vp c12 has almost 5 grams of lead per gallon. Just mix in 20% you get an increase in octane and the extra lead gives a increased resistance to sticking pistons.

    One bad tank of 93 octane pump gas could detonate a 93 octane pump gas motor to the grave. Adding some race fuel is insurance against a bad or mis-labeled tank of fuel. It is not uncommon to get a bad tank occasionally, even at your favorite pump. You really never ‘know’ what you get at the pump. At least with race gas it is color coded. VP c12 is green

    Triple pipe motors should always have some lead in the tank imo. Especially a pro 785... Even with stock compression.

    Mixing leaded race fuel with 93 pump gas is Good insurance for an expensive motor imo.

    I always throw in a couple/few gallons VP c12 per tank.

    allcool

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