Proper Octane?

[oppermancjo]

Apologies if this is a repeat. I'm pretty sure I read something about this somewhere on the forum but a few searches later and I can't find it.

I don't remember how I came to the realization but I learned that Stihl recommends 89 octane fuel in my MS 290. I've owned the saw for several years now and have always used 87. I finally used up the last of my 87 mix and filled the can with 89. WOW!! I can't believe the difference in how that saw runs. It's like a brand new beast! I'm not saying it ran poorly on 87 but it runs so much better on 89!

Would I see any benefit by going with 91 or even 93 octane? Do I run the risk of damaging the saw?

Thoughts and comments are appreciated.

 

[Uncle John]

I think 91 octane non ethanol is the way to go.

 

[blades]

Unless you go with AV fuel, everything around my metro area is Ethanoled.

 

[msvold]

I'm fortunate to have one local fuel station that has 93 octane no ethanol fuel. Only thing I burn in all of my two stroke engines. I buy two gallons at a time - so 20 - 30 cents extra a gallon is worth it. I recently visited my favorite saw shop - he made a comment that he is seeing saws purchased within weeks coming back due to low octane and ethanol fuel. He said, "but I never see you guys." Yeah, 30 cents extra a gallon, better performance, no issues. Can't even mail a Christmas card for that.

 

[Uncle John]

I'm fortunate enough to have a nephew that delivers the non ethanol fuel to the station. So he can buy me 5 gallons right after it is dumped. Its probably 35 miles from me. So he takes it home and I pick it up there.

 

[Rsquared]

I just mixed up 2 gallons of Stihl mix with 89. Now I can't wait to try it..

 

[KenJax Tree]

Do you need to us different oil ratios with different octane gas?

 

[Whitespider]

My 2-cycle engines have never run quite right on 87-octane...
They ran good on ethanol-free 89-octane when I could get it, but now all the 89 is 10% ethanol in my area.
I use ethanol-free 91-octane in all the 2-cycle engines and I can't tell the difference between it and the 89 (when I could get it).

Really, in my opinion, any ethanol-free gasoline, from 89 to 93-octane is about perfect... an octane level over 93 is just a waste, and probably hurts performance a little bit (too high an octane can reduce performance as much as too low an octane).

...And no, the oil mix ratio does not change with higher octane.

 

[oppermancjo]

Do you need to us different oil ratios with different octane gas?

I read through my owner's manual and I believe the answer is no. I tried to copy and paste from the PDF version of the owner's manual I have and it wouldn't let me. Says use 89 octane and 50:1 oil/gas ratio.

I have access to non-ethanol gas somewhat nearby. It's probably a 45 minute round trip so I'm not sure if it's worth it for just a few gallons of gas... I'd like to try it someday though as I've heard it makes a huge difference.

 

[wudpirat]

Don't be thrifty (cheap)

My saws and ATV's get 93 Super Shell.
I have to run 91+ in my turbo VW.
In stations that dispense all grades from one nozzell, I fill my gas cans last .
That way any 87 or 89 left in the hose goes into the car.
The lawn tractor and log splitter get whats ever in the general gas can, 87 or 89 they don't care.
Three oz of oil per gal for 2 cycles, mid 40:1.
Heard the EPA has approved E20, now the fun begins.

 

[Patrick62]

run what tickles ya

opcorn:

are fuel threads getting as popular as oil threads?

Everybody got their own favorite theories on this.

The only common thing I see is that most agree that ethanol don't belong in there.

 

[darkbyrd]

93 with sea foam for all my small engines.

 

[Whitespider]

Everybody got their own favorite theories on this.

All theories aside, just the facts…
“Octane Rating” has nothing to do with the amount of power stored in the gasoline; the “octane rating” is simply a way to rate the gasoline’s resistance to ignition. All sorts of additives can be used to increase the “octane rating”… traditionally lead (tetraethyl lead) was used and is still used in aviation fuels. Interestingly, when air and gasoline are mixed (such as in an engine cylinder) its resistance to ignition increases as it is compressed… it is most easily ignited when the piston is at the bottom of the intake stroke, before compression begins.

The use of a fuel too low in octane will result in detonation… this is when heat and pressure cause the fuel/air to ignite at a secondary spot in the cylinder after the spark plug ignites it. When this secondary flame front meets the primary flame front you will hear this as “pinging” or “spark knock” in larger 4-cycle engines (like in your car); you won’t hear it in a small high-RPM 2-cycle engine (like your chainsaw). Over time, detonation can destroy an engine… piston and ring damage, cylinder scoring, and whatnot. And worse, detonation can lead to pre-ignition (fuel ignites before the spark plug fires)… which is almost always immediately catastrophic in nature. Detonation can cause a “hot-spot” on the piston, eventually hot enough to cause the fuel to pre-ignite… and typically this happens at the bottom of the piston stroke when the air/fuel is easiest to ignite. As the piston is coming up the compression stroke the fuel is rapidly expanding, pressure builds off-the-chart… something has to give, and usually that’s the top of the piston (hole in the piston top). You won’t hear any pinging or knocking from pre-ignition… you just end up with a pile of junk.

The reason your engine seems to run better with 89-octane fuel is all about the timing. All internal combustion gasoline engines make the most power when peak cylinder pressure is reached at 14[sup]o[/sup] after-top-dead-center. If you use a fuel too low in octane the fuel ignites to fast and peak cylinder pressure is reached earlier than 14[sup]o[/sup] after-top-dead-center, too high in octane and peak cylinder pressure is reached later than 14[sup]o[/sup] after-top-dead-center. The closer peak pressure is to 14[sup]o[/sup] after-top-dead-center, the more power it will make, and the better it will run. Back in the days when a good engine mechanic could tune your car engine timing “by ear”… that’s what he was doing, finding that “sweet spot” where cylinder pressure peaked at 14[sup]o[/sup] after-top-dead-center. I find that most small, high-RPM, 2-cycle engines like 91-octane fuel the best… but 89 and 93 put them pretty darn close also. One more thing to consider… two-stroke oil lowers the octane rating of the fuel.

One final warning about running a fuel with too high an octane rating. Higher than needed octane will cause incomplete combustion and excessive carbon deposits… this in turn can be a major cause of detonation and/or pre-ignition and immediate catastrophic engine failure.

 

[KenJax Tree]

I use 93 octane E10 with Belray H1R 40:1 if my saws meet death from that then so be it.

 

[z50guru]

One final warning about running a fuel with too high an octane rating. Higher than needed octane will cause incomplete combustion and excessive carbon deposits… this in turn can be a major cause of detonation and/or pre-ignition and immediate catastrophic engine failure.

Sounds like im stuck between a rock n a hard place :msp_confused: All my local pumps add ethanol. I dont want that, so i buy AV100 from the local air strip. But then i dont want the above mentioned symptoms w/ using to high of an octane.. What would you guys use? treated 93 pump, or AV100 w/o the ethanol? Curious. Thanks

 

[bubba3228]

I read through my owner's manual and I believe the answer is no. I tried to copy and paste from the PDF version of the owner's manual I have and it wouldn't let me. Says use 89 octane and 50:1 oil/gas ratio.

I have access to non-ethanol gas somewhat nearby. It's probably a 45 minute round trip so I'm not sure if it's worth it for just a few gallons of gas... I'd like to try it someday though as I've heard it makes a huge difference.

If they have a restaurant or diner that serves bacon and a nice stack of pancakes it will definitely be worth the Sunday morning drive, take momma on a date...:msp_smile:

 

[mr.finn]

I have been running 89 with Red armor oil at 50:1 for the last 9 months or so. Before that was Husky oil. I use this same 89 fuel in all my 2 cycles. String trimmers, BP blowers, saws. The blowers have it the worst, running wide open for anywhere from 30 min to an hour straight. Never had a issue. Was at the dealer a week or so ago and he said the only thing with 50:1 is the margin of error is slim. I now mix 40:1. Will probably stay with 89 unless dealer recommends going to 93.

 

[Whitespider]

Sounds like im stuck between a rock n a hard place :msp_confused: All my local pumps add ethanol. I dont want that, so i buy AV100 from the local air strip. But then i dont want the above mentioned symptoms w/ using to high of an octane.. What would you guys use? treated 93 pump, or AV100 w/o the ethanol? Curious. Thanks

I know a lot of guys here run AV100LL (low lead) fuel without issue. Really, if you run your small 2-cycle hard, the excessive carbon deposits with high(er) octane fuel is more the exception than the rule… and the way I understand it, if you’re using a synthetic two-stroke oil it will keep things pretty darn clean all on it’s own. Personally, I’d be more concerned about the lead in aviation fuel contributing to deposits in the combustion chamber (but, again, maybe synthetic oil would negate that).

Truthfully, I wouldn’t use ethanol blended fuel in any 2-cycle if I had any other choice. And also, truthfully, I don’t see the need for synthetic oil with the fuel I can get… so I don’t use it. But if I were you, with what you have available to you (and it-is-what-it-is), I’d keep using the AV100LL (because I have a personal disdain for ethanol blended fuels, and octane too high is less danger/trouble than too low) mixed with a full synthetic 2-stroke oil (to keep things clean)… and not fret about it, because it-is-what-it-is.

But I have a question… Are you absolutely, 100% sure there ain’t any ethanol-free pump fuel within 30-40 miles of your location??? It might be worth the drive every so often.

 

[JimiLL]

I know a lot of guys here run AV100LL (low lead) fuel without issue. Really, if you run your small 2-cycle hard, the excessive carbon deposits with high(er) octane fuel is more the exception than the rule… and the way I understand it, if you’re using a synthetic two-stroke oil it will keep things pretty darn clean all on it’s own. Personally, I’d be more concerned about the lead in aviation fuel contributing to deposits in the combustion chamber (but, again, maybe synthetic oil would negate that).

Truthfully, I wouldn’t use ethanol blended fuel in any 2-cycle if I had any other choice. And also, truthfully, I don’t see the need for synthetic oil with the fuel I can get… so I don’t use it. But if I were you, with what you have available to you (and it-is-what-it-is), I’d keep using the AV100LL (because I have a personal disdain for ethanol blended fuels, and octane too high is less danger/trouble than too low) mixed with a full synthetic 2-stroke oil (to keep things clean)… and not fret about it, because it-is-what-it-is.

But I have a question… Are you absolutely, 100% sure there ain’t any ethanol-free pump fuel within 30-40 miles of your location??? It might be worth the drive every so often.

Is there a good way to find out who has any non ethanol, besides driving to every gas station within 30 miles?

Anyway im in NJ... highly doubt theres any around here. I guess 100LL it is for me as well. Thats cool though, its what I run in the atv

 

[zogger]

Apologies if this is a repeat. I'm pretty sure I read something about this somewhere on the forum but a few searches later and I can't find it.

I don't remember how I came to the realization but I learned that Stihl recommends 89 octane fuel in my MS 290. I've owned the saw for several years now and have always used 87. I finally used up the last of my 87 mix and filled the can with 89. WOW!! I can't believe the difference in how that saw runs. It's like a brand new beast! I'm not saying it ran poorly on 87 but it runs so much better on 89!

Would I see any benefit by going with 91 or even 93 octane? Do I run the risk of damaging the saw?

Thoughts and comments are appreciated.

Any premium and especially non ethanol youll see a diference. Plus the non ethanol will last longer and help eliminate fuel damage issues. Much above low 90s in octane though is a waste of time unless you are running a super built real high compression saw.

89 from most pumps is a nice compromise though, because it is usually blended from the high test and the 87. The high test will invariably not move as fast as the el cheapo, so a little staler, and the el cheapo part will always be the freshest.

I go ahead and run full 93 octane no ethanol, because I can get it and the owner told me he moves some gallons so it is fresh, mostly to hot rod kids and guys with powerboats. He does a nice business with a big sign that says NO ETHANOL.

Ive tested my mix on some cheap saws to see how long it lasts, three months and it is still good. Havent tested it beyond there because I just used it up. Im happy with three months, allthough I get fresh mix much more often every two weeks or so when I am cutting a lot, sometimes weekly (two gallons at a whack). Supposedly just a month and mix isnt good, but mine with the echo oil with the stabilizer in it seems to last pretty good. Straight gas, the 93 in my 4 stroke small engines, seems it lasts until I crank something up again. I get that ten gallons at a whack and it is always good it seems, tiller will sit all fall/winter and into early spring and start two or three pulls at the most.

I tell ya what is *real* good mix, trufuel in the can. Expensive, but its the best. Claimed two year shelf life, and I believe them. If I was only using small amounts of two stroke mix a year, Id just use that stuff.

Everyone should grab a few cans and try it, not only to get a blast from the past with real" gasoline, but because then you have the perfect mix can! Those round quart sizes are tops to carry mix out into the field with you. Mix it up in a larger can, then funnel it into the quart cans. poutrs easy even in small cap access challenged saws, and the cans it in your jacket pocket perfect. plus, they are metal and already labled clearly as two stroke, 40 or 50 to 1, no making any mistakes then.

Ive got two cans unopened put away,(three have been used and recycled now into my mix cans) will use them this winter and replace them, figure two cans a year, eventually Ill have enough to mix up and can big batches. Want to get to the point I am doing mix in five gallon batches, mixed at 40 to 1, full synthetic oil, with additional Pri G stabilizer..