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Old 08-25-2009, 09:53 AM
branwell is offline
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Northern, Va
Joined May 2006
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Re: Low octane fuel or High octane fuel??

Hi,

I have a DA100L and BME116 on pipes. Both of them sound like there are rocks in the exhaust when running on 87. Sound goes away when running 92. Me thinks the noise is detonation related.

Branwell
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Old 08-25-2009, 10:45 AM
diviatix is offline
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Woodstock, Ontario, Canada
Joined Oct 2007
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Re: Low octane fuel or High octane fuel??

As I understand it, a lot of "regular" octane rated gas has up to 10% ethanol added, while the higher octane rated gas tends not to.

I have been told that ethanol is bad for the diaphragms in our carburetors (hardening etc.) .

I read the labels on the pumps at a few local gas stations, and yes, the lower octane gas does have ethanol while the higher octane gas does not. So I use the higher octane in my low compression engine to extend the life of my carburetor components.

I see no performance difference, but I like the idea of avoiding ethanol since I trust the "guru" who passed the info along to me.

My .02

Cheers,

Andrew.
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Old 08-25-2009, 10:50 AM
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United States, WA, Seattle
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Re: Low octane fuel or High octane fuel??

Higher octane fuel can tolerate higher compression or backpressure (as is the case when running pipes), higher timing advance, high prop load, or higher combustion temperatures.

My ZDZ engines have closer to 10:1 compression ratio (can't recall the exact number right now) and MUST run on the higher octane stuff.

Run the lower compression engines with a light load prop and no exhaust and moderate timing and good coling air flow, and low octane gas will work fine every time. However install a pipe, run a heavier prop load, modify the ignition timing point, etc., and "standard expectations" give way to reality.

There is nothing wrong with experimenting a bit to find what works best for our particular situations. If the engine runs better on 93 octane (or 87 octane or 100ll octane or 60octane white gas), then by all means continue to use it! FWIW 100LL actually smells much better than car gas and some people run it without problems, although they need to change their spark plugs far more often than on automotive gas (the lead in the gas plates the platinum electrode of the plug).

Where I live ALL the gas blends have "up to" 10% ethanol, so I don't have a choice. I believe most states are this way now, or at least the New England states, and all the states along the I-80/I-90 corridor to the west coast did when I moved and swapped the Atlantic for the Pacific ocean last year. I believe some states still have ethanol-free gas though.
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