What octane is best, and why

[davidwyby]

87 lights easier, snortier, more prone to predetonate

 

[Powerstroke Cowboy]

87 lights easier, snortier, more prone to predetonate

Probably requires less timing as well to get the same amount power. With that said, I wonder if running more timing with 91 would make it closer to 87?

 

[Woodsman]

According to the US owner‘s manual that Swabian saw is designed to run on mid-grade unleaded gasoline with a minimum octane rating of 89. Octane values less than that can result in higher operating temperatures resulting in an increased risk of piston seizure.

So, for the Stihl 500 use a non-ethanol unleaded fuel of an octane of 90 to 95? And, a oil ratio at 32:1 to 40:1 ?

Higher octane above 89 helps the Stihl 500 run cooler right?

 

[davidwyby]

95 might be a bit much.

My ported 3120 couldn’t burn 110 completely while milling

 

[huskihl]

So, for the Stihl 500 use a non-ethanol unleaded fuel of an octane of 90 to 95? And, a oil ratio at 32:1 to 40:1 ?

Higher octane above 89 helps the Stihl 500 run cooler right?

87 is fine if it’s fresh. Octane depletes as it gets old, so after awhile 87 is no longer 87. More octane is just more resistant to pre-ignition. The idea behind running 90-95 is so a year down the road the gas in your can or tank still has enough octane so that you won’t have pre-ignition and erode the crown of the piston away.

 

[pbillyi69]

didnt someone do some testing and determined that pre ignition in a chainsaw isnt possible?

 

[huskihl]

didnt someone do some testing and determined that pre ignition in a chainsaw isnt possible?

I believe it’s detonation that doesn’t have time to be possible, but I’m not sure. I have heard the same thing though. One of them is definitely possible because I’ve seen lots of pistons with the exhaust side crown eaten away from using stale gas

 

[pbillyi69]

I believe it’s detonation that doesn’t have time to be possible, but I’m not sure. I have heard the same thing though. One of them is definitely possible because I’ve seen lots of pistons with the exhaust side crown eaten away from using stale gas

stale gas the octane is much lower so you think that is burning up the piston because it gets too hot from pre detonation or just getting too hot?

 

[huskihl]

stale gas the octane is much lower so you think that is burning up the piston because it gets too hot from pre detonation or just getting too hot?

I’ve had saws keep running after the switch was turned off. Old fuel or low octane causing something inside to glow red hot (likely the spark plug electrode) and acting like a glow plug. Similar to a pre 90’s car dieseling for a few seconds with the key off.
It’s the light ends? or something like it evaporating that makes the fuel more volatile

 

[davidwyby]

…and I’ve had saws surge at idle like they wanna take off on their own after long hard cuts.

Makes one wonder what’s going on in there while cutting.

 

[Nutball]

I mentioned before that I had a 2188 run quieter on 93. 87 & 89 wouldn't do it. Probably gained a smidge of torque. It's the only saw I've noticed the issue with, but I often don't pay attention if it's not my saw, though I still try to get premium for company saws. Mine always get premium.

 

[Woodsman]

…and I’ve had saws surge at idle like they wanna take off on their own after long hard cuts.

Makes one wonder what’s going on in there while cutting.

Do you remember what octane fuel and fuel/oil ratio you were running in that saw?

 

[huskihl]

…and I’ve had saws surge at idle like they wanna take off on their own after long hard cuts.

Makes one wonder what’s going on in there while cutting.

There’s no four stroking 20–30 seconds after the cut. I’d say that’s likely borderline on having enough fuel and it was getting hot. Could also be old fuel causing it to get hot

 

[davidwyby]

There’s no four stroking 20–30 seconds after the cut. I’d say that’s likely borderline on having enough fuel and it was getting hot. Could also be old fuel causing it to get hot

Bof

My big ported saws have to be considerably fattened up in big wood in the heat

 

[davidwyby]

Do you remember what octane fuel and fuel/oil ratio you were running in that saw?

Old 87 with ethanol

32:1 red armor probably

 

[davidwyby]

I mentioned before that I had a 2188 run quieter on 93. 87 & 89 wouldn't do it. Probably gained a smidge of torque. It's the only saw I've noticed the issue with, but I often don't pay attention if it's not my saw, though I still try to get premium for company saws. Mine always get premium.

My 2188 is LOWD

 

[Woodsman]

Old 87 with ethanol

32:1 red armor probably

Have you tried running non-ethanol with 91 to 95 octane rating? It might run cooler.

 

[pbillyi69]

My 2188 is LOWD
View attachment 415378

that looks like it might set that dried up desert wood on fire
edit...looks to be short a couple of screws too

 

[davidwyby]

Have you tried running non-ethanol with 91 to 95 octane rating? It might run cooler.

That’s what I run now most of the time. It’s not readily available so if I’m doing a bigger project I run local eth and put the non in before I store it.

 

[davidwyby]

that looks like it might set that dried up desert wood on fire
edit...looks to be short a couple of screws too

Just Like Me! On both counts