High Octance Gas Conundrum

[decompiler]

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!

 

[eljefino]

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.

 

[Darwin]

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

 

[Skyliner70cc]

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.

 

[Ghost0]

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.

 

[decompiler]

And now I know.

Thanks everyone!

 

[Simonator]

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

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.

 

[SirJakesus]

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.

 

[Warner]

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.

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.

Warner

 

[brett_maverick]

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.

Brett