Octane--Is 87 REALLY Right?

[SacramentoMike]

Yes, I know it's recommended and everything. I don't suppose it's really required, but called for in the owners manual and of course here, in the "Bin O'Facts," etc. But this morning a couple gardeners on the radio were talking about tree pruning with a chain saw. They seemed to know small engines, and one stated you should never put 87 octane into a chain saw--said it "burns too hot" and could damage the saw. The other agreed.

Yes, I know 1300 cc's isn't a "small engine," but I'm still wondering, and I've been thinking about this lately anyway. I've been feeling the heat a lot since I recently lost a heat deflecting panel on the road somewhere.

So to those with the technical chops to answer, does the lower octane indeed burn hotter? And if so, would that translate to more engine heat that could be reduced by an octane bump? These two guys, by the way, said they believe higher octane in their cars gives them better mileage too.

Thoughts? And please don't blast too hard. I know the "87 octane" question sounds like it's heading for NEPRT land under the sub-heading "stupid questions," but I'd appreciate some discussion along with the hard time. Thanks.

 

[yanktar]

Actually, yes, in very loose terms. Higher octane burns cooler which is why it's needed to prevent pinging.

But if the octane is too high, it will foul your plugs. Too low, and it will burn them.

Some people think they should use higher octane in the winter, but this is wrong, If anything, go up in the summer so the engine runs a little cooler.

Small engines tend to run hotter and, of course, are air-cooled, not liquid cooled so 91 or higher is better for them.

 

[ionbeam]

IMO -- with some basis in research and education

Gasoline grades all start with a similar base to which 'stuff' gets added (see top tier grade gas). The additives may be for emissions, cleaners and octane boosters. The primary difference between octanes is the blending of the additive package. The ping/detonation difference in fuel blends are additives which make the fuel molecules harder to break apart under pressure and temperature. The temperature after ignition doesn't basically change. Lower octane fuels will ignite at lower temps/pressures (by a small amount) but the temperature of the burning fuel isn't significantly different once ignited. The higher octane fuels will be harder to ignite unless the engine has higher compression or higher cylinder head temperatures.

IMO Alert #2 -- Running a lower octane gas in an engine won't create excessive heat unless the engine is silently knocking. OEM manufactures are real good at specifying the fuel requirements of their engines, run the fuel they recommend. If an engine like the FJR recommends 87 octane you will be wasting your money for fuel with higher octane because there is no need, and in fact, your mileage and performance may be less due to running a fuel that is harder to ignite.

Flame suit on.

NNEEPPRRTTTTTTT

 

[rushes]

I don't know if it burns hotter or not, but if you can feel the difference in octane on your legs, you might have royal blood.

I think I would just replace the heat deflecting panel.

https://en.wikipedia.org/wiki/The_Princess_and_the_Pea

 

[Geezer]

My STIHL chainsaw manual specifically calls for mid-grade fuel. That would be 89 octane. It also specifies to not use corn free fuel because the additives used instead of alcohol may harm the engine.

My FJR gets 87 octane, or even 85 octane when at higher elevations. Whatever is the least expensive stuff available when I stop for gas.

 

[rushes]

NNEEPPRRTTTTTTT

Pretty fancy!

(I-beam's bored...)

 

[ionbeam]

NNEEPPRRTTTTTTT

Pretty fancy!

(Ibeam's bored...)

See the way I ignited this low content pressure, low temperature thread?

Then again, I could be drinking Beemerdons standard already...

 

[SkooterG]

Really? Really??? Really??????

Google is your friend........

Your farts will have more impact on perceived heat than octane ever will. Why didn't you start this on a Friday?

 

[Pterodactyl]

I was in the paddock at the Barber Motorsport Park a few weeks back. They had pumps that operate just as any gas station pump only they had 110 octane available (at $9.40/gallon). Guess I should have tried some. Evidently my FJR would have run at absolute zero.

 

[SkooterG]

Evidently my FJR would have run at absolute zero.

 

[Bugnatr]

In eastern Nevada and Utah they have 85 octane. The only time my 04 stumbled off the line is when I put 85 in it.

 

[TomInPA]

Put the air deflector back in and worry less. I do use higher octane for my 2-cycle very high compression chain saw, blower and trimmer. These are all less than 5 cc and operate at high RPMs and ignite on both strokes. Hardly comparable to the FJR. I've never had a ping on the FJR with regular fuel unless I lugged the engine at low RPM and high load. I consider the regular fuel requirement a blessing since it is widely available, and clearly the engine is tolerant of a wide variety of fuels. No harm in running premium fuels, but it won't noticeably cool the engine.

Doug has a good point. I have used 85 octane, but usually get a mid-grade when in higher altitudes areas, especially if I will be transiting to lower altitude. 85 works great on the 12,000 foot+ hill climbs in Colorado.

Come back East this time of year and you'll appreciate the extra leg warmth.

 

[RossKean]

For the last two fillups of the season, I will put premium in the tank. Around here, premium does not contain any ethanol and that is my preference for the 3.5 months of inactivity. Otherwise, it does just fine with regular.

 

[Ignacio]

I know the "87 octane" question sounds like it's heading for NEPRT land under the sub-heading "stupid questions,"

Then why didn't you, at least, look at the various threads on the subject in Best of NEPRT first? Did the tree pruner/engine experts also talk about batteries losing charge when they sit on concrete floors?

 

[Pterodactyl]

Here in MT we are considered high altitude so 85 or 85.5 octane is sold in some places in place of 87 octane. When I encounter this I opt for mid-grade 88 octane.

Spousal Unit's bike requires 91 octane. When we ride and refuel together, which is the norm, I put 91 octane in the FJR too.

 

[PhilJet09]

What they said.

Plus, are you really basing this question on what a gardener told you about a chainsaw?!

You do realize that the FJR mill and a chainsaw are very different motors, right? In almost every way, right? Four stroke vs two, fuel injected vs carbureted, liquid vs air cooled, ECM vs err, not, four cylinder vs one...

Come on, man!

 

[Mihalis fjr]

In Europe you find only 95 & 100 octane.When i use 100 octane the bike runs stronger for sure,especially at the acceleration it is very noticeable and it is not a placebo!I did not noticed any difference if the bike runs hotter or cooler..

 

[bluesdog]

In Europe you find only 95 & 100 octane.When i use 100 octane the bike runs stronger for sure,especially at the acceleration it is very noticeable and it is not a placebo!I did not noticed any difference if the bike runs hotter or cooler..

Isn't European method of calculating octane different from that used in North America?

 

[Ignacio]

In Europe you find only 95 & 100 octane.When i use 100 octane the bike runs stronger for sure,especially at the acceleration it is very noticeable and it is not a placebo!I did not noticed any difference if the bike runs hotter or cooler..

Isn't European method of calculating octane different from that used in North America?

Yes. 4 to 6 points higher compared to North America. NEPRT threads make me chuckle sometimes....the amount of self-declared precision butt dynos are AMAZING!