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Best Octane for 2 cycle engines

Posted by cranheim (My Page) on
Wed, Jul 30, 08 at 16:55

I have been using premium gas (93 Octane) in my fuel mix for all my 2-cycle engines for many years. The manuals have said to use 89 octane or higher. The three choices in my area are 87, 89, or 93. I remember reading somewhere it is better to chose the higher octane gasoline. However, my STIHL dealer told me the other day I would be better off using the mid-range (89 octane) because the premium gas (93 octane) has too many additives in it to bring up the octane rating that may cause problems with the engines. I called STIHL, and all they would say is that I should use 89 octane or better. They saw nothing wrong with using the premium or higher octane gas. The person I spoke with just said the higher octane fuel is a product from better refining, rather than more additives, therefore should be cleaner burning. Has anyone else run into this question? I know others have said they use regular gas and never had a problem. I don't care about the extra cost for premium, gas because I am a homeowner and don't use that much a year. I just want to use what is best for the engines. Charles Ranheim


Follow-Up Postings:

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RE: Best Octane for 2 cycle engines

I just switched all my 2 cycle equipment to AVGAS100LL. It's less then $1.00/gal above regular and keeps fresh for years vs. weeks and 2 cycle engines love high octane.

I've had it with crappy quality oxygenated automotive gas with ethanol.



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RE: Best Octane for 2 cycle engines

davefr
Do you think the premium (93 octane) is worse than the 89 octane mid-range gasoline sold at the pumps like the STIHL dealer thought? Where do you buy the aviation gas?

Charles Ranheim


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RE: Best Octane for 2 cycle engines

The manual for my ten year old Stihl 026 chainsaw says to use minimum 89 octane "named brand" fuel and if it unavailable, to use premium fuel.


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RE: Best Octane for 2 cycle engines

No, I can't imagine any scenario where premium would be worse then mid range. Every Stihl dealer I've ever talked to says to use premium if possible.

I buy AVGAS from a small airpark. It's actually closer to where I live then the nearest gas station. Go to any small airport and they'll help you out. I'd avoid the major airports.


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RE: Best Octane for 2 cycle engines

I use name-brand (Shell/Exxon) 89 octane and marine Sta-bil year round.


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RE: Best Octane for 2 cycle engines

Ive been running my 30yr old Stihl 041 Farmboss all that time on 87 octane mixed 32:1 instead of recommended 40:1. It runs fine and I have yet to clean the exhaust ports.


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RE: Best Octane for 2 cycle engines

I buy OPE fuel when I fill the van and I'm too lazy to flip the lever and re-swipe the card for a couple of galloms just for the hand-held stuff. I have a large can for straight 87 octane and use that to make smaller batches of mix. I haven't noticed any pinging in the small engines but then again I'm not sure what pinging sounds like at over 7,000 RPM. I could be killing the equipment slowly but haven't had any fuel related problems or burned pistons.

The 2 strokers I have run around a 8:1 compression ratio max and although ignition advance factors in, I just don't think it's a big deal. The Feds now require all grades of gas to have a detergent package so I think this is a left over recommendation from years past. What I'm trying to say here is that I think the manufacturers are more concerned with the detergent package than the octane requirements. Just my opinion and it certainly could be wrong. Just don't run 'em to lean.


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RE: Best Octane for 2 cycle engines

Thanks to all who responded. I will probably continue to use premium (93 octane) in my 2-cycle engines. Most stations I go to have a single hose to fill the tank after selecting the grade of fuel. If you only by a gallon at a time for 2-cycle engines, and you select 89 octane after someone just purchased 87, there is a good chance you will be getting a hose full of 87 octane first before the 89 gets to the end of the hose. In this case, you would not be getting the full 89 octane you paid for. I know this sounds picky, but it gives me another reason to select the 93 grade to be safe. When buying only a gallon or two, the difference in price will not break me. Charles Ranheim


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RE: Best Octane for 2 cycle engines

I'm not hundred percent certain, but I heard that the gas stations have tanks for 87 and the highest octane either 91 or 93. If you select a mid grade like 89, the pumps draw gas from both tanks and mixed them together to come up with the selected octane rating. Like I said, not sure if this is correct, but its what I heard. Either way, use 89. Your equipment was designed for that and a performance increase from using 93 will be very minimal if any at all. Unless your equipment is running really high compression ratios there is no need for 93, but if it gives you piece of mind then use the 93. No harm in that, just more expensive.


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RE: Best Octane for 2 cycle engines

I used to work for a Shell distributor. Some of our stations had dedicated midgrade tanks, and others blended at the pump.


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