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Fuel Used in Gas Engines

Old 09-08-2009, 06:15 AM
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musalami
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Default Fuel Used in Gas Engines

Greeting everybody,

What is the right octane % (91 or 95) for fuel used in gas engines?

Thank you.
Old 09-08-2009, 07:00 AM
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ec121
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Default RE: Fuel Used in Gas Engines

Depends on the compression ratio.. ZDZ says to use 93. Others say 89. There is no octane for all makes. I read the other day that 93 or 91 will work for all, but if the engine is designed for a lower rating, you won't get any more bang for your buck. I personally use 93 because I have one ZDZ in my stable. I use it for all my gassers to keep from having more than one jug.
Old 09-08-2009, 07:00 AM
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w8ye
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Default RE: Fuel Used in Gas Engines

Most engines need the lower one.  (91)
Old 09-08-2009, 08:12 AM
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musalami
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Default RE: Fuel Used in Gas Engines

How about DA & DL Engines?
Old 09-08-2009, 10:07 AM
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altavillan
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Default RE: Fuel Used in Gas Engines

The higher octane rating means the combustion heat/pressure can be higher with higher ratings. Power remains about the same. Preignition starts at a higher temp/compression rating with a higher octane rating. Regardless of what engine a higher octane rating will give a little more room for a lean hot running engine and or help the engine run on hot summer days.
Most engines will run fine on regular gas. The extra octane is like a bit of insurance. That said the high compression engines, and I'd include DL in there will be less likely to have preignition/detonation with the higher ratings.
Old 09-08-2009, 02:29 PM
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Bob Pastorello
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Default RE: Fuel Used in Gas Engines

Original poster is in Saudi Arabia....don't know for sure, but haven't there been discussions before about differences in octane ratings??? I was under the impression that Non US octanes were numbered "higher", but in fact were "regular" US, composition wise. I don't know ..... just adding the comment about the OP.
Old 09-08-2009, 04:22 PM
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JOHNS3D
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Default RE: Fuel Used in Gas Engines

i use 87, the other one here on the gas station is 92 which is the same thing.
Old 09-08-2009, 04:28 PM
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pe reivers
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Default RE: Fuel Used in Gas Engines

It is perhaps wise to consider octane rating in different countries.

European engines are designed around regular 95 (RON) research octane numbers (was 93 ron)
American engines are designed around regular 87 (PON) pump octane numbers

Pump octane is : (Research octane + Motor octane)/2
Motor octane is typically 8 points lower than research octane, less in very good fuels like Aspen (alkylate, 95 ron/93 mon) Some rumours state 10 points difference. Don't belive them. It's from the old sandy oil well days!

so considering European 95 RON, that would be (95 + 87)/2 = 91 PON or US premium fuel. That would well serve all motors worldwide.

Personally I consider this a non-issue. I use 98 RON. No engine will object to that. I did find problems however in using low quality fuels. Better be safe than sorry.
Race fuel or airplane fuel is not required though. In any of our standard engines premium 91 PON will be excellent!

PS
If you want to run a MVVS 26cc on 87 pump gas, you need to add TWO EXTRA head shims.
Old 09-08-2009, 06:02 PM
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Default RE: Fuel Used in Gas Engines

Opinons of this scenario.

Living on the Southwest Florida coast, with thousands of boaters and many marinas, I have easy acess to 90 octane, "non-Ethanol" gasoline.

Or, 89 octane, "non-Ethanol" ValvTech gasoline.

Cost is reasonable. Any benefits to this option; or negatiives, for that matter? Operating DLE types, 50cc and 100cc.

DR
Old 09-09-2009, 01:36 PM
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Jezmo
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Default RE: Fuel Used in Gas Engines

Can't speak for anything else but my DL50 and Zenoah G26 run just fine on whatever the wife brings home for the weedwhacker (usually 87). I just steal her fuel and take the tongue lashing the next weekend when she needs fuel again. LOL If I have time I run out to the lake and get some ethanol free 91 at the marina but most times it's her 87 octane weedie fuel.

P.S. My DL is in the 125 hr range now and still running strong. Also, my MVVS 26GT HAS to have the 93 or it will detonate and run hot.
Old 09-09-2009, 03:06 PM
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Tired Old Man
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Default RE: Fuel Used in Gas Engines

The Middle East has some wide fluctuations in their octane levels. I've seen regular unleaded gas arrive with octane levels ranging from 84 to 91. The purpose of higher octanes was to minimize the possibility of pre-ignition under higher compression loads. With a two stroke timing shpould not be changed in an attempt to extract more energy from the fuel. That can be done with four strokes, but not so readily with two strokes. Lower octanes subjected to high compression can self ignite (like diesel) as the temperature increases during compression.

In any case, most of the commercially available gassers we use will not gain any measurable amount of power by using higher octanes. However, some (3w, MVVS, Evolution, ZDZ) will eliminate pre ignition issues since they were designed around higher compression ratios.
Old 09-09-2009, 06:17 PM
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pe reivers
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Default RE: Fuel Used in Gas Engines


ORIGINAL: Jezmo

Can't speak for anything else but my DL50 and Zenoah G26 run just fine on whatever the wife brings home for the weedwhacker (usually 87). I just steal her fuel and take the tongue lashing the next weekend when she needs fuel again. LOL If I have time I run out to the lake and get some ethanol free 91 at the marina but most times it's her 87 octane weedie fuel.

P.S. My DL is in the 125 hr range now and still running strong. Also, my MVVS 26GT HAS to have the 93 or it will detonate and run hot.
The mvvs is designed at the max compression ratio if you use 91 PON fuel. Adding a shim under the head will further improve the engine's running sweetness. Adding two shims, and it will allow the engine to use 87 octane (US PON)
Old 09-10-2009, 10:54 AM
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Default RE: Fuel Used in Gas Engines

Jezmo,

I need to have you and your wife over to dinner one night (when I return from the desert). Anybody that can get his wife to go get the lawn fuel has got my respect! Add to that, SHE is the one that would notice you used some of it. I am not worthy! Mine wouldn't ... oh, I won't go there.

As said otherwise above, use regular. There is no power increase available in higher priced fuels.

Bedford

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