Octane

Discussion in 'Motorized Bicycle General Discussion' started by Hot Wheels, Sep 5, 2011.

  1. Hot Wheels

    Hot Wheels New Member

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    Just wondering what octane gas everybody is using, I usually run premium 93 octane, but I saw a gas station that had 100 octane racing fuel so I bought a gallon to try it out. So far it seems that new motors don't really like it, kills the top end. But older motors like it excelerates faster and runs a little cooler. Thanks for your replies.brnot
     
  2. 2door

    2door Moderator
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    Don't waste you money on high octane fuel. The benefits are small, if any, and the only one who will be thrilled is the oil company you're buying the high priced stuff from. These little engines (you didn't tell us what you have) will run and perform just fine on low octane fuel. You need to be aware that the ethanol content will effect things like rubber or neoprene parts eventually. Fuel lines, gaskets, 'O' rings, etc will see a shorter lifespan the higher the alcohol content.

    Tom
     
  3. Hacksawdecap

    Hacksawdecap New Member

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    Straight up wisdom!
     
  4. Hot Wheels

    Hot Wheels New Member

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    I'm using 80cc 2 stroke, Tom thank you for your wisdom.
     
  5. BarelyAWake

    BarelyAWake New Member

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    While it's true that these low compression engines don't require high octane fuel, that they may even run worse... there's other, perhaps less obvious problems with the so-called "premium", issues that are somewhat regional & are consequences of both ethanol and the high cost of fuel.

    Ethanol is a solvent and has a very limited "shelf life" due to it's nature. As a solvent, contaminants in fuel are at an all time high. While there's often been concerns stated regarding the deterioration of the elastomers (rubber-like parts) like the seals and other components of our fuel systems, the "fuel lines, gaskets, 'O' rings, etc" previously mentioned, remember that the fuel has been in storage before you purchased it and it's been having it's effect on the station's tanks, lines and gaskets.

    There's also the phase separation issue, water & alcohol mix quite easily whereas water and gasoline does not, if enough water is introduced into the fuel through exposure and time (condensation & even ambient humidity) the water will be drawn into the ethanol and the mixture will separate from the gasoline, forming a layer at the bottom of the tank, leaving three very distinct layers - the top being mostly low octane fuel as the octane number had been raised by blending in ethanol (and it's likely the higher the octane rating, the more ethanol had been added), the middle being mostly water with some alcohol and the very bottom the sludge created from it's solvent properties - and bear in mind that the pumps don't draw fuel from the top of the tanks.

    These effects are bad enough, but what makes them worse is few to no gas stations ever bother to clean their tanks let alone upgrade their pumps to compensate for the alcohol content, and with the cost of fuel - many folks don't buy the quantities of the higher octane "premium" that would be needed to ensure what you're getting is clean, "fresh" fuel, it's likely to have been sitting in that tank for far too long.

    Remember, the advised "shelf life" of an ethanol blend by the time you get it is only about 2-4 weeks, but that's depending on how long it sat in storage & exposure, which you can't know except for the obvious, and that's the "cheap stuff" sells far more than the "premium" ...how long did the "premium 93 octane" sit in the gas station's tanks, dissolving years of varnish and phase separating? Is it really even close to "93 octane" anymore? Is it worth what you're paying? What are you really getting for your money?

    *shrug* No way to really tell as it does depend on regional variables, but I do know this - I built myself a custom tank, obviously new and spotless I get my fuel from only the one gas station and despite the fact I buy the most popular "cheap stuff" which is clearly the freshest, newest fuel available with the tanker truck refilling the underground tank at least once a month, that once spotless tank of mine now has a layer of black, slightly gooey sludge that bears a remarkable resemblance to what dissolved pump hose would look like, after only one summer of riding...

    Some "fuel" for thought lol ;)
     
    #5 BarelyAWake, Sep 6, 2011
    Last edited: Sep 6, 2011
  6. tommyboy1442

    tommyboy1442 Member

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    i just thought id add, i recently ran 118 octane fuel by vp with some synthetic oil(not sure what kind), and that motor ran great off it. started easier, ran stronger, and it smelled great, but at $20 a gallon, ill stick with bp 89 .
     
  7. Dan

    Dan Staff
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    I use 87 or 89 octane. I experimented with all grades in 4 smokers. (87 to 93) and found it made less difference then the weather if it made any at all.

    I have not been able to find ethanol free gas here in CT. This discussion got me thinking. Just filter it out. Seems like a no go. filter out ethonol - Google Search

    So thought just use fuel stabilizer and a water separator. Overton's® > Fuel Filter/Water Separator - Boating & Marine > Fuel Systems > Fuel Filters : Marine Fuel Tanks, Gas Tanks, Parts, Boat Fuel Accessories, Fuel Supplies

    Then I thought, forget this. snicker
     
  8. Fulltimer

    Fulltimer New Member

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    That filter looks pretty good.

    Terry
     
  9. Tohri

    Tohri New Member

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    There should be a major caveat here: 87 works great unless you're running madman high compression ratios.

    Stock motors will not see any difference. One of my personal bikes will barely run on 87.
     
  10. Greybeard

    Greybeard New Member

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    I've spent 50 years with racing 2 strokes, and large 4 stroke engines. Have seen just about every type of failure possible, and the majority of them have to do with detonation.
    When I see post after post about head gasket failures, it makes me wonder if the "conventional wisdom" is wisdom at all. Any engine, when working against high heat, excessive timing, or too low of octane, will detonate under high load. Most of these little engines are running at WOT more than any thing else. Higher octane reduces the speed of the burn, which in turn reduces the maximim cylinder pressure the engine has to contain. Too fast a burn and cylinder pressures spike, blowing head gaskets, pulling studs, breaking rings and pistons. High temps increase the odds of uncontrolled burn and high cylinder pressure.
    An engine that is on the verge of detonation is running high cylinder pressure which will make good power until it breaks. Higher octane won't make more power, it's value is a more controlled burn.
    You don't hear detonation. In some cases you can feel it. A racing smallblock Chevy will lose it's smoothness, you'll feel it and hear it as roughness or vibration.
    There's an old saying, before my time, that "the poor can't afford to buy cheap". If you have lots of money and can afford to fix or replace what you have, it doesn't matter what octane, or kind of oil, or % of mix you use. If you rely on your equipment, can't afford the breakdown, my opinion is to not try to save 20cents on a tank of fuel.
     
  11. Nashville Kat

    Nashville Kat Active Member

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    Isn't the rating of a gasoline just a reflection of how much it's refined?
    or in other words, how much less it is like oil or diesel fuel and more like gasoline?

    So then we come along with two cycle motors and add oil back into it-

    I've used a little middle grade, but it doesn''t seem to make much difference

    of greater consequence seems our oil to fuel mixture.

    I've always run Carb cleaner/ gas treatment/ injection cleaner- which is all pretty much the same I think- "Petroleum distilate" highly refined gasoline
    in my cars the last 35 years and they never gum up
     
    #11 Nashville Kat, Sep 6, 2011
    Last edited: Sep 6, 2011
  12. 2door

    2door Moderator
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    I hear you and don't disagree yet I've seen these comparisons here before and you can not compare these simple, mostly stock Chinese 2 stroke engines to highly modified V8s or Harleys, Hondas or BMW power plants. Predominately the engines on the majority of the bikes built and ridden by the people here are not modified in any way and specifically in terms of compression ratio. They are not "high compression" engines by nature and my guess is that the failures you mention, head gaskets, stud, pistons etc" are a result of improper assembly and maintenance (proper torque values) by the unskilled. Couple that with questionable manufacturing tolerances and you have the results you've mentioned.

    Absolutely no arguments with your advice, if, we were all running kick butt mouse motors or blown big blocks on our bikes but we're not. Therefor my original statement stands. Octane rating has little to do with our little toy engines and how they'll perform. :)
    Tom
     
    #12 2door, Sep 6, 2011
    Last edited: Sep 13, 2011
  13. Nashville Kat

    Nashville Kat Active Member

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    About the head gaskets- I replaced a cylinder recently- "the jug" and then something got inside and scoured the cylinder- so I took it apart again- I've been playing around with two different 50 cc jugs- and I found that I got a lot of return with a couple of files-

    it seems they just aren't finished off that well- and you really can see that if you take a file to the head- and ditto for the top side too-

    file flat against them and they get really shiney and smooth comapared to what they were- the thin metal gasket can only benefit when in use then
     
  14. Hot Wheels

    Hot Wheels New Member

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    I've learned alot from all you guys, thank you for sharing your knowledge.
     
  15. dmb

    dmb Active Member

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    long ago engines were overbuilt and for the time lasted a long time. a 36 hp VW would last years and some are still around. but advance the timing too much [i time by ear] don't adjust the valves and these well built robust low hp motors were not long for this world. now these cheep china motors come apart on their own with out any help from hi-compression hi-rev's alot of them self destruct on their own. i wonder if the russian motors were built better? too bad japan didn't make them.
     

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