Opinion on octane and ethanol

[Fred482]

Ethanol octane ratings vary but most users say it's in the range of 110-113, pure racing grade methanol can be as high as 120. Methanol has a higher latent heat of vaporization, thus provides more cooling during the evaporative process. If run rich, 5.5:1 AFR, it can support compression ratios of up to 20:1.

Corrosion issues aside, the key to making parts live in a race engine is heat, if it runs rich on methanol, the parts stay cool enough to survive. The down side is, when rich enough to save all the parts, it becomes hard to get it to burn.

I used to measure the cylinder head temps (5 HP Briggs Motor Sports block, aftermarket head and internals, Tillotson carb, straight methanol fuel) before and after a run with my daughter's junior dragster and found them at 125 degrees F at the start and just over 200 F at the finish line. Gasoline temps were higher, 185 F at the start and near 310 F at the finish. This with the carburetor adjusted for best performance.

 

[Simonizer]

The octane number of a gasoline is a measure of its resistance to knock. Gasolines with high octane numbers burn more smoothly and are thus more effective fuels. (If in a situation where the compression ratio and/or operating temperatures warrant this) The more highly branched alkanes have higher octane numbers than the straight-chained alkanes. The octane number of gasoline is obtained by comparing its knocking characteristics with those of "isooctane" (2,2,4-trimethylpentane) and heptane. Isooctane is assigned an octane number of 100, whereas heptane is assigned a number of 0. Gasoline with the same knocking characteristics as a mixture of 90 percent isooctane and 10 percent heptane is rated as 90 octane. If you guys remember back a few years, the anti-knock agent added to gas was tetraethyllead. Very effective but catalytic converters hated it, and kinda poisonous lol. Most anti-knock agents are now oxygenated hydro-carbons, especially methyl t-butyl ether (MTBE). I personally don't like ethanol enhanced gasoline in 2-strokes because it seems to dilute or break-down the boundary layer of lubrication between the piston and cylinder wall. If your saw is not knocking or pinging under load, don't waste your money on a higher octane gasoline. If it is, go up in increments. My Grand National had a knock detector that would dump excess pressure from the wastegate of the turbo. That car loved Chevron 94, it allowed it to build 17psi boost. Sorry to blather on but it is hard to take the geek out of the engineer.

 

[Jim Mesthene]

e-10 has and will cause problems on many newer saws.

What problems, exactly?
All the products are adjusted to run lean, but they're all adjusted to tolerate E-10 too. I agree that running a little richer is better.
Assuming you make that adjustment, what problems do you expect when you say it will cause problems? All we can get around here is E-10, but my 36 year-old Pioneer, and my 4 year-old Husqvarna don't seem to care, as long as it's fresh.

 

[sachsmo]

I agree,

like I said earlier, millions of saws are running it, I have too.

Is it ideal for small engines,,,,,,,,,,,,,,?

me thinks there are several newer saws that had issues contributed to lean seizures, most are blamed on e in gas.

But hey there are people out there that can wreck an anvil in a sandbox eh?

I do know most the people in this part of the country will be pushing for e-15 and higher in the future.

 

[eMGunslinger]

me thinks there are several newer saws that had issues contributed to lean seizures, most are blamed on e in gas.

The husky 575xp I think is a good example, as well as the ms391....I do not think it runs well in strato. All total I have probably rebuilt 10 each of those 2 saw and seen over 40 burned up in a short amount of time and can vouche for 1/2 the people running the saws

 

[Jim Mesthene]

I do know most the people in this part of the country will be pushing for e-15 and higher in the future.

God save us all from that.
I'm no fan of E-10, much less E-15. I'm a tree-hugging liberal with guns and chainsaws, but no matter which hat I'm wearing, I think it's stupid to subsidize turning food into bad fuel. Nodody benefits except for ADM.

 

[Mad Professor]

There have been long discussions on this and the folk lore of the amazing 93 oct...people (Bsnelling) has done tests on it and I have witnessed it as well as having no added advantage. Octane is a rating in the US generalized by the AKI (Anti-Knock-Index) which is specific to certain motors for making them knock when you try and use inferior fuel....EX-My 06 GTO can only run 91-93 due to 11:1 compression which is roughly 220psi. I have a saw that compresses at 190psi and runs 93 but that is a little different. Most work saws are in the 150psi range. Honestly you could probably run them on 80 octane if there where such a thing

Octane Rating-basic measurement of the fuel's tendency to burn in a controlled manner, rather than exploding in an uncontrolled manner

Detonation will quickly ruin saws run on 80 octane fuel. The only engine I can run that in , is my 1940 ford 9N, that is 6:1 and new runs 100 psi , static compression.

Try some of the older "red" AV fuel, or Coleman "white gas", if you want to "knock" your saws socks off.

Also, effective compression ,is different than measured compression, on both 2 and 4 strokes.

Things that effect static compression are valve timing and port timing, what you really get when it is running, and under load, determines the anti-knock properties of the fuel needed.

P.S. When I rebuilt my 1969 LT1 350 chevy ( "11: 1" stock compression), I decked the block, and surfaced and CCed the heads. The machining should have raised the compression...

All the cylinders were within a psi of 190 psi, static compression, with a snap-on gauge.

If you have 220 psi on an ethanol burner, you gauge is wacked.

 

[lambs]

I've always heard that the additives in higher octane gas mean there's less actual gas in the mix; therefore worse gas mileage. Doubt it matters so much in a saw, but I won't run 93 in mine. If it was high compression, I'd still go with the manufacturer's recommendation as long as I haven't modded the saw.

 

[CJ8Ted]

Good info on this thread.
Just got back from filling my mix jug and the small station that sells non ethanol was not selling any gas today and guys were working around the tanks fill caps. "no gas today" I got some red desel and talked to the clerk. No more non ethanol in Pa. they were cleaning the tanks and getting them ready to switch to E gas. I use Sta-bil and sware by the stuff. With luck and keeping the E-gas fresh I will not be on the rebuild path with any of my gas engines.

Ted

 

[sunfish]

I don't like the fact that we have ethanol in our gas, but I haven't have any problems with it.
I usually buy 89, or 91 octane.

 

[Cstratton]

I've always heard that the additives in higher octane gas mean there's less actual gas in the mix; therefore worse gas mileage. Doubt it matters so much in a saw, but I won't run 93 in mine. If it was high compression, I'd still go with the manufacturer's recommendation as long as I haven't modded the saw.

Refineries use a cocktail of chemicals to acheive thier octane ratings. It depends on a lot starting with the base stock. You never know what you are getting from one tank to the other. I don't think fresh E10 is going to hurt anything. But I have seen people ruin alot of good parts not religiously purging the methanol out of thier engines.

 

[promac850]

God save us all from that.
I'm no fan of E-10, much less E-15. I'm a tree-hugging liberal with guns and chainsaws, but no matter which hat I'm wearing, I think it's stupid to subsidize turning food into bad fuel. Nodody benefits except for ADM.

You got that right. It's a waste of taxpayer's money, and a waste of valuable resources. IIRC, it's something like 2/3 of all of the agricultural land in the US is set aside for crappy corn that is used to make that damn ethanol. I say we go back to leaded gas, or find a better alternative to ethanol. A little bit of lead never hurt anyone, a lot of it is what gets to you. I'm sure the concentrations were of minimal sizes and did little to no actual harm to anyone and their kids. A toddler eating leaded wall paint, well duh, it's a lot more concentrated as it basically qualifies for a flake of lead. On the other hand, the minute fumes disperse quickly outside.

OP, don't start with me... I can rant about everything that's wrong with ethanol and show how the benefits are smaller than most of the US populations' brains.

 

[Cstratton]

You got that right. It's a waste of taxpayer's money, and a waste of valuable resources. IIRC, it's something like 2/3 of all of the agricultural land in the US is set aside for crappy corn that is used to make that damn ethanol. I say we go back to leaded gas, or find a better alternative to ethanol. A little bit of lead never hurt anyone, a lot of it is what gets to you. I'm sure the concentrations were of minimal sizes and did little to no actual harm to anyone and their kids. A toddler eating leaded wall paint, well duh, it's a lot more concentrated as it basically qualifies for a flake of lead. On the other hand, the minute fumes disperse quickly outside.

OP, don't start with me... I can rant about everything that's wrong with ethanol and show how the benefits are smaller than most of the US populations' brains.

Leads downfall was more due to what it did to catalytic converters when those came in the 70's. If I'm wrong correct me as I was still pretty young then.

 

[promac850]

Leads downfall was more due to what it did to catalytic converters when those came in the 70's. If I'm wrong correct me as I was still pretty young then.

Yep, catalytic converters would have to go. Oh well.

Someone would have to figure out an oxygen sensor that can last a long time without fouling up with lead. Once that's done, you could run leaded gas in any car with an O2 sensor.

 

[hammerlogging]

I've read through this thread, i haven't kept too much abreast of this topic except to know that ethanol is supposed to be bad. I run 660s run about 2 gallons of 93 mix a day. I quite frankly don't take the time to even consider of its E10 or not, it seems like it always is anyhow, but I pretty much just say #### it and carry on, though I don't care for the guilt I have knowing I might be able to seek out some straight gas. Anyhow, is it bad? maybe, probably, heck, Madsens's had a write up about how bad it is. Has it affected me, no.

Atleast my gas stays fresh, so it sounds like thats good. And I don't seem to run my first saw more than a year or so before it goes back to a backup, maybe that helps. Oh well, carry on folks. Thanks for the info.

 

[BiodieselNC]

I will definitely stick to Ethanol-free gasoline. Which is what I have been running the past few months and really like it. Of course I have trimmed every limiter tab on every adjustment needle on every 2-stroke engine I have. I can tune rich for ethanol, but prefer e-free gasoline.

So it sounds like 89 octane is probably fine for me? All of my saws are north of 150psi, i think the highest is 175.... So is 91/92 necessary for that range or can I get by on 89 and not have to add any octane booster?

 

[promac850]

I will definitely stick to Ethanol-free gasoline. Which is what I have been running the past few months and really like it. Of course I have trimmed every limiter tab on every adjustment needle on every 2-stroke engine I have. I can tune rich for ethanol, but prefer e-free gasoline.

So it sounds like 89 octane is probably fine for me? All of my saws are north of 150psi, i think the highest is 175.... So is 91/92 necessary for that range or can I get by on 89 and not have to add any octane booster?

If you don't hear any pinging, you're good to go. 89 sounds like it should work. Make a small batch of mix and try it in all of your saws. If any need higher octane because of pinging, then go up in octane rating. Otherwise, stay with what you have.