High Octance Gas Conundrum

Discussion in 'General Questions' started by decompiler, Jun 18, 2008.

  1. decompiler

    decompiler Member

    Because I weigh so much (270 pounds), I cannot use Regular grade gasoline. All grades of gas here in the USA are being cut with 10% Ethanol. And running a low octane gas thinned out with 10% octane makes my Happy Time engine run terrible. Oh, it just runs sooooo ratty and has no power whatsoever. So I use the 93 Octane grade because of the presence of 10% ethanol, it acts like 89 grade Octane in my engine. (Actually, 93 acts more like an 84 grade with 10% ethanol...)

    The only real place I can get gas at is a Shell station. And their gas has that "V-tech" engine cleaner additive in it. It's supposed to help carbon deposits and other gunk from settling on your cylinder walls. But in the case of these two-stroke engines, they need that slick film that builds up on the cylider walls, right? Because two-stroke engines get their lubrication from the oil added to the gas. So are engine additives put in the mix by the gas station companies negating (or annhilating) the lubrication properties of the two-stroke oil?

    You know, just curious!
    Last edited: Jun 18, 2008

  2. eljefino

    eljefino Member

    I read (on bobistheoilguy.com) that shell's v-power has a lubricity enhancer, ie a top end lubricant... so in my mind that's a good thing and should help the 2-stroke oil do its job.

    The virgin gas they cut with ethanol is a couple octane points low, as the ETOH boosts it. Works well in the 4-cycle cars. Wonder if you're running into "sensitivity", ie, the split between research and motor octane not being in your favor with the gas you get.

    I cannot claim any expertise in octane and 2-strokes, so I'll stop right here, and hope to read more.
  3. darwin

    darwin Well-Known Member

    Id bet you a tank of gas [mab tank] that we do a blind test with your bike on 3 different days using all 3 different octane fuels and when it was over you couldnt tell me on which day we used the 87 octane.[low grade] Every new/used car I get I always try some higher octane gas to see if it runs better and I never can tell the difference. Ive always owned basic vehicles so which manufacturer recommends 93 octane I dunno, must be a mercedes or a beemer? I dont even know why they make the stuff. Here in denver our regular is 85 octane because were so high up and every thing seems to run just fine. JMO
  4. Skyliner70cc

    Skyliner70cc Active Member

    Your statement is not supported by facts:

    Pure ethanol has an octane rating of 110-113. A 10% ethanol mixture would not lower the octane rating of fuel.

    At approximately 6.5:1 compression ratio, octane is not an issue with these engines.
  5. Ghost0

    Ghost0 Guest

    Octane rating has to do with the knock point as measured on a single cylinder 4 stroke where they can change the compression ratio until the engine knocks. This is an industry standard and is how all fuels are measure. There is another method and I can't think of it right now. The reason a fuel knocks is due to preignition. The reason a fuel preignites is due to it's flash point. Lower octane fuels have a higher flash point. Given that our 2 strokes, and sorry if your is a 4 stroke, have a compression ratio of 6 to 1, we have no need to eliminate knock. In fact due to the lower octane having a higher flash point you will get better performance out of it than you will out of higher octane. Just my 2 cents worth.
  6. decompiler

    decompiler Member

    And now I know.

    Thanks everyone!
  7. Simonator

    Simonator Guest

    Exactly. We could probably get away with 70 octane. I will NEVER put any higher than 87 octane in my happy time tank. If anything, premium might actually hurt performance. Premium fuel only needs to be used in high compression engines, or engines with a turbo or supercharger.
    Last edited by a moderator: Jun 19, 2008
  8. SirJakesus

    SirJakesus Guest

    Yeah I've always had to use premium fuels in my street motorcycles but everything else, including small 2 strokes and 4 strokes I use 87 octane. Theres just no reason to go any higher.
  9. Warner

    Warner Member

    Agreed. 87 octane should be what you use. You may in fact find (probably WILL find) that your engine makes LESS power, runs HOTTER, and gets LESS mileage with premium fuel. Its burn rate (flame speed) is too slow for such a low compression engine. The problem with the ethanol additive is that you need to burn MORE ethanol compared to regular gasoline, so your mileage will drop with the ethanol mixed fuel. In an MAB it's probably not even noticeable, but in a car it would be.

  10. brett_maverick

    brett_maverick New Member

    I sell a lot of the China import scooters/mopeds with a 49.5cc engine. The owners manuals claim that 90 octane gasoline is the minimum requirement. They all have the Honda GY6 clone engines with no timing adjustment. I started experimenting with fuel types/octane ratings and found the following to be true.

    All of the brands we sell say not to use ethanol enhanced fuels. 87 octane fuel runs terrible; 92-93 octane fuel makes them run worse than that! 89 octane fuel with "no ethanol" seems to be the happy medium. 90 octane leaded fuel works the very best. It's available at most farm cooperatives here in the midwest. It's red in color; and actually smells like gasoline.

    A product called "Marvel's Mystery Oil" can be used as an additive to any gasoline to provide excellent upper cylinder lubrication.

  11. Warner

    Warner Member

    One thing to remember about recommended octane levels coming from other countries is that they have different rating systems. Japan and Europe use a system called RON or Research Octane Number to determine the octane rating of their gasoline, while stateside we use a system called AKI or Anti-Knock Index to determine gasoline's octane rating... Interestingly, to further complicate things it would seem that our own AKI system is actually derived from the average of the RON system and another more complicated system referred to as MON or Motor Octane Number... So, to recap our methodologies for measuring gasoline's octane rating are different, but share some common elements...
    So, with the commonality of RON in mind a good rule of thumb is as follows, multiply the foreign RON Octane rating by 0.95 and you will have the US AKI equivalent.

    ( RON Octane Rating x 0.95 = AKI Octane Rating )
    90 RON Octane x 0.95 = 85.5 AKI Octane (US measure)
    98 RON Octane x 0.95 = 93.1 AKI Octane (US measure)
    100 RON Octane x 0.95 = 95 AKI Octane (US measure)

    So, as you can see the 93 or 94 octane fuel we are all paying an arm and a leg for is actually quite comparable to the higher octane fuels found in Europe and Japan. I suspect that the recommended 90 Octane rating that you are getting from the Chinese motors is based off of the RON Octane rating and would equate to AKI (or US method) Octane rating of only 85.5


    PS - What compression ratio do those Chinese engines run at?
    Last edited: Jun 20, 2008
  12. mcassMB6

    mcassMB6 Member

    SO....what is the bottom line? These HT engines that most of us run (2 strokes)...are they a low or high compression engine? And ideally, based on that, should I be running 87 or 93?

    Which is it? Aghhh!
  13. Ghost0

    Ghost0 Guest

    Our Happy Times are relatively low compression and you should you use the lowest octane gas you can.
  14. eljefino

    eljefino Member

    Coincidentally if the fuel you buy has red it's dye, and meant for off-road use because there hasn't been road tax paid on it.

    I wonder how the green dye of most 2-stroke oil would affect it.

    Legally, you CAN use road-taxed leaded fuel if you can find it, as our HT motors have no "unleaded fuel only" disclaimer. Even my lawnmower has that!

    OT, but I got a couple gallons of "white gas", aka coleman fuel, on post-winter closeout for $1/gal. I used it all up in my mower last summer. It worked great! It's a real low octane unleaded fuel... low b/c of it has no additives at all for boosting octane so it burns clean in camp stoves or whatever. My briggs mower calls for, IIRC, 77 octane, LOL.
  15. brett_maverick

    brett_maverick New Member

    HT's are low compression engines. (6.0:1 to 7.5:1) The "plastic fantastics" a.k.a. china scooters/mopeds are relatively high compression. (9.0:1 to 10.5:1) The "Happy Times" bikes should run fine on any low grade fuel. The China scooters run best on 89-90 octane leaded fuel.

  16. BSA

    BSA Guest

    Has anyone tryed using this coleman fuel on happy time engines. Was there any pinking when you ran it on your lawnmower. I'm thinking this coleman fuel is tax free thus cheaper.