What octane is best, and why

[SOS Ridgerider]

Here’s a thread for discussing the octane of fuel, and why some are better than others.

Keep it civil.

 

[wcorey]

Alright I'll sum it up and keep it as civil as I can...

Anyone who's been around here long enough and isn't a clueless knowitall ahole knows 87 makes the best power in a saw.
Or so I've heard on the internet.
Or something.

There, I feel all better now...

 

[srcarr52]

85 non ethanol if you can find it.

30% nitromethane if you don’t mind dealing with it.

 

[ayoungtexan]

87 no ethanol

 

[SOS Ridgerider]

Alright I'll sum it up and keep it as civil as I can...

Anyone who's been around here long enough and isn't a clueless knowitall ahole knows 87 makes the best power in a saw.
Or so I've heard on the internet.
Or something.

There, I feel all better now...

I don’t think you were the problem in that discussion Bill. Lol.

 

[Mastermind]

I banned the troll anyhow. I'm not going to tolerate narcissism.

 

[Kiwioilboiler]

And US MON/AKI octanes are not the same as other continents RON octane labelling, so a foreigner might suggest the "wrong" octane unwittingly.

 

[Sawrain]

You could see the problem in his name.

TT, twin turbo, boosted applications need octane, as they are generally knock limited.

We however have the luxury of being able to find MBT, maximum brake torque/minimum best timing mostly free of knock.

My view is that you can say of the commonly available pump fuels the lower octanes have proved to be the fastest with a chainsaw.

But that does not really make the statement lower octane fuels make more power true, faster burning yes, BUT octane rating over all fuels does not correlate well with flame speed, however it kind of does within the scope of normal non oxygenated pump fuels, add in all available fuels, not so much, throw in hydrogen, natural gas, N-Heptane (Zero octane equivalent), Iso-Octane (100 Octane equivalent), oxygenated and others (I lost the study ) and the flame speed vs octane correlation mostly goes away.

Faster burning lower octane fuels can make more power in non knock limited cases, such as ours, but an even faster burning higher octane fuel would likely make more.

We buy fuels based on octane ratings for cars that do have knock problems, but we don't have a knock problem here, and when knock isn't a problem you have the luxury of buying fuel based on other characteristics, and luckily for us the cheaper lower octane fuel happens to possess what we want, good flame speed.

 

[Eduardo K]

I had a guy tell me why he buys only high octane for everything. I felt bad explaining to him that it’s just the hydro-carbon ratio of heptane and octane, and it’s only required for high compression or engines equipped with forced induction. Essentially, I tell them what Sawrain said, but I always get the feeling they don’t believe me.
I think the octane marketing might have surpassed the farm boss marketing.

 

[av8or3]

It’s all about flame travel. When you introduce anti -knock compounds in gasoline it’s to slow down flame travel. It does that by making the flame “jump over” the molecules of anti-knock additive. When you have high octane fuel it means it literally takes longer to burn. That would be helpful in a high compression engine, preventing things like pre-ignition and detonation somewhat. Back to flame travel. The flame moves faster when the gas molecules are closer together. To slow the flame travel down you put stuff in it’s way. Lower octane has less stuff to get in the way, so the flame travels faster, producing more power in its allotted time in the cylinder. 87 non ethanol is the way to go.
There, octane 101.

 

[rogue60]

Around my parts the new EPA low octane pump gas not made for industrial 2T's is rubbish. Kero makes more power in my saws lol
Wish I could go back in time and get a few 44 gallon drums of real pump fuel ahh the good old days...

 

[BK13]

Unfortunately, the only non-ethanol around here is all 91+ octane premium.

 

[cus_deluxe]

had a guy tell me he ran 110 in all his (stock) saws, made crazy power. i said ok...

 

[srcarr52]

had a guy tell me he ran 110 in all his (stock) saws, made crazy power. i said ok...

People like that should be forced to wear warning labels.

 

[Hinerman]

People like that should be forced to wear warning labels.

This might be a dumb question. Besides the octane level, what are the differences between 87 and 91 octane. Is 91 octane cleaner? whatever that means...

I always buy 91 on the assumption that it burns a little cleaner. I use it in all my 2-strokes and my 4-stroke splitters and riding mower. Am I wasting my money?

I have easy access to both e-free.

 

[av8or3]

It’s not a dumb question. In my opinion, you are wasting your money. I don’t know about cleaner. But your equipment will run better on 87 octane.

Not totally related but kinda. In ‘98 I bought a new Jeep Cherokee. Nice truck. I thought so much of it that I started using Premium gas in it. Not long after when accelerating up a hill, the truck would start to misfire. I thought it was a trans problem for some reason but after checking it out and talking with the tech, he advised me to switch back to regular. It fixed it.

 

[CR888]

Around my parts the new EPA low octane pump gas not made for industrial 2T's is rubbish. Kero makes more power in my saws lol
Wish I could go back in time and get a few 44 gallon drums of real pump fuel ahh the good old days...

I remember on our way to the boat ramp as a kid dad would drive through a BP service station and fill up the boat with good ol ZOOM 2T mix right outta the pump. It all went down hill since then.

 

[CR888]

10 years ago 99% of saw forum members were all running full synthetic 2T oil, premium high octane gas & could justify it with pages & pages of guff, interesting how that's all changed now.

 

[FederalQ]

Unfortunately, the only non-ethanol around here is all 91+ octane premium.

Same here, and at times nearly $1 a gallon more than regular. Plus only one nozzle for all grades.

 

[srcarr52]

This might be a dumb question. Besides the octane level, what are the differences between 87 and 91 octane. Is 91 octane cleaner? whatever that means...

I always buy 91 on the assumption that it burns a little cleaner. I use it in all my 2-strokes and my 4-stroke splitters and riding mower. Am I wasting my money?

I have easy access to both e-free.

The more refined, premium fuels such as 91 and 92 octane seem to have a better shelf life than the lesser, cheaper cousins, and there is the ethanol issue with lower grade fuels. This is the primary reason why I run premium verses the other that usually give just a little more power. Chainsaws and other power equipment have a tendency to sit a long time with fuel in them. I've had chainsaws sit in my garage for 2+ years with BP premium start with no issues.