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Old 12-19-2011, 11:34 AM   post #16 of 32
Canawler
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Default Re: High Octane on small engines?

Quote:
Originally Posted by Jere39 View Post
Common wisdom here is there is less ethanol in the higher grades (octane), based on how hard/expensive it woud be to blend a 10% ethanol fuel with enough octane boosters to get 91 or 92 octane.
That's actually kind of backwards. Ethanol itself has a higher octane rating than gasoline. In the lower grades the ethanol is the booster, so to speak. They can start with gasoline with octane ratings below 87 an add the alcohol. But you are correct about the higher grades having less alcohol. At least with one oil company exec I spoke to, I was told their premium 93 octane had no ethanol and the midgrade was a blend. They supplied basestock to multiple gasoline companies who would then mix in their own additive packages as the delivery trucks would pick up at the refinery.



Quote:
Originally Posted by john9001 View Post
i buy my OPE fuel 15 gals at a time from the same station, always 87 octane and test each batch for ethanol, i have found 4%-6% and the last batch was 0%.

the pump just says ,"contains ethanol". state law says it canot be more than 10%.
when i find ethanol i use stabils ethanol treatment.
I'm surprised to hear that the ethanol was testing that low. From the reading I've done on one of the oil forums, it seems most people that actually test their fuel find the ethanol content is actually much higher than the 10% allowed.
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Old 12-19-2011, 11:49 AM   post #17 of 32
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Default Re: High Octane on small engines?

Just to add a bit on my experience about octane ratings and my old cavalier's behavior...

I had a '89 Cavalier with a 2.0L 4 cyl back in high school. These engines are relatively low compression and not an overly hot ignition either... on cold damp mornings with older plugs those cars let you know they were due for plugs, it'd cough and sputter for a couple minutes warming up and if you dared put it in drive and hit the gas it usually would conk out on the spot!! One time I decided to try hi-test in it just to see if it would help out the power/economy/etc. (it had a good set of plugs at the time). The next morning (it was a warm summer morning) when I started it it coughed, sputtered, and died a couple times before it heated up enough to reliably ignite the hi-test; it was behaving as badly or worse than with old plugs on a chilly damp morning!! After heating up for a minute all was good and I couldn't discern any other difference in the hi-test fuel. Needless to say, I NEVER ran higher than 87 in that car again!!
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Old 12-19-2011, 12:18 PM   post #18 of 32
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Default Re: High Octane on small engines?

I haven't found anywhere nearby that sells non-ethanol 87. I've been using 93 in everything for years and haven't had any issues. My 1989 Toro still starts right up and runs strong and has great compression. All I've ever done to that engine is change the oil and spark plug, I've never had to clean the carb out or anything. My pressure washer and tractor are both from the mid 80's and both work perfect too, I've had to clean the carbs in those over the years, but compression is still perfect and no smoke. I sure haven't found a downside to running 93 octane, and any extra expense is sure worth it to not have the ethanol.
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Old 12-19-2011, 05:51 PM   post #19 of 32
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Default Re: High Octane on small engines?

Quote:
Originally Posted by Jere39 View Post
Very thoughtful perspectives on this always controversial subject. I think the OP had a very specific question related to ethanol, rather than the traditional octane question. And I'd echo his interest. Here in PA it is very hard to get reliable info on ethanol content. Most pumps are labeled something like "Contains up to 10% Ethanol", and most pumps dispense 2, 3, or 4 grades of gas, typically 87, 89, 91, and even a few 92 octane. Common wisdom here is there is less ethanol in the higher grades (octane), based on how hard/expensive it woud be to blend a 10% ethanol fuel with enough octane boosters to get 91 or 92 octane. And therefore many small engine repair shops, especially 2 cycle shops recommend 91 octane. Not so much for the octane rating, but to ensure lower to no ethanol. Of course, they also recommend a fuel stabilizer and an ethanol remediation additive.
FWIW, for my chainsaws and line/brush trimmers I use 91 octane from a local brand name station and add Startron Enzyme Fuel Treatment an the new synthetic 50:1 2 cycle oil. Might be over kill for the chainsaws that run pretty much every week cutting firewood, but the brush cutters take long winter breaks.

And I am first to admit I have no petroleum engineering degrees, so please consider my post opinion if you prefer.
A few years ago, it was only thr Low test gas tht has ethanol in most stations, but today, if one has it, almost 100% likelyhood all grades have it.

National limit is 10%...but Ive personally tested over 30% from all the major grades of gas.
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Old 12-19-2011, 06:26 PM   post #20 of 32
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Default Re: High Octane on small engines?

This may or may not relate to our smaller engines but it is well proven that using HT in lower compression bigger engines costs HP, I did not agree and had to try it. I have a 383 in my wet ride it on a good day will run 65.5 on 87, my CR is 9.125. I decided my own testing was in order, I have two tanks I emptied one and put 10 gallons of 93. My other tank was straight 87, I ran it up and did my 65.5 on the 87. I switched tanks and ran it a few minutes to clear the lines of the regular, I ran it up and only got 63.2. Switched back again ran it a few minute to clear the HT ran it and got right back up to my 65.5. Needless to say I will not run HT unless nothing else is available at the dock.

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Old 12-20-2011, 01:55 AM   post #21 of 32
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Default Re: High Octane on small engines?

High octane produces less power. That is what it is designed to do. It is because of the heat generated from the higher compression engines, that you get more power. Confused? Ok, the lower the octane, the more volatile the fuel is, the more powerful the explosion. The more any fuel is heated, the faster it will burn. More heat causes higher volalite reaction. This is why you need extra fuel on a cold engine, when you choke an engine, you are putting in exta fuel until the engine warms up, because the fuel is not volatile enough. Higher compression engines produce more heat, which needs less volatile fuel. (Higher octane) But, when you put higher octane in a lower compression engine, it will produce less power than if you ran 87 octane because of the volatility. But, if you run higher octane in a lower compression engine long enough, it will eventually have more power. And the reason is this, it will start to carbon up bad enough to actually raise the compression. Then if low octane fuel is used, then it will ping because of the "higher" compression caused by the carbon. I believe that any damage caused by higher octane fuel when "not" needed is either from carbon coming loose, or someone putting in the lower octane fuel in a "carbon compression raised" engine and pinged itself to death.
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Old 12-20-2011, 08:42 PM   post #22 of 32
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Default Re: High Octane on small engines?

club
the last two post are basically what i want to say
i ran a Pro Stock garden tractor puller for ten years.
a big block onan 60 c.i. T 260 / P 224
start at 7.0 comp. ratio. advance at 21 degrees.
after many mods 9.25 comp ratio.
i ran a mix of 103 and 87 octane. advance at 27 to 29 degrees.
this was by slotting the ign. module
now the rest of the story.
for eight of those years i was the scale/tech. inspector.
a local ( now well known) puller always used ava fuel in the stock off lawn class.
our rules stated pump gas only.
you can SMELL the ava. fuel.
GUESS, what? he passed the tech. every time.
he would have needed 13 to 14 comp ratio and about 36 to 42 degrees
of advance to do any good.
SO, run 87 octane, that is all you need.
thank you. boomer (the used onan engine parts guy)
p/s this is a LONG story for me
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Old 12-20-2011, 11:25 PM   post #23 of 32
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Default Re: High Octane on small engines?

So what's the verdict? I've read about how bad ethanol is for small engines. Would it be advantageous to use non ethanol 91?
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Old 12-21-2011, 10:27 AM   post #24 of 32
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Default Re: High Octane on small engines?

The verdict is simple. A motor that is designed to run on 87 will see no benefit from running on 91. If you let your gas sit for long periods you run the risk of a slight drop in octane but at that point you are running stale fuel and if there was ethanol in the fuel it is likely that there is some phase separation (water) present.

I run the 91 ethanol free in all of my seasonal equipment but only at the end of the season for storage. Other than that there is no downside to using the 87 ethanol on equipment that is regularly used. The exception to that would be old equipment that does not have ethanol compatible components in the fuel system. In that case it's time to replace the lines anyways.

Basically, use what the motor was designed for. Race fuel will mot make your car into a race car but race cars are designed for race fuel and require it. Your lawn mower operates the same way.
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Old 12-21-2011, 11:42 AM   post #25 of 32
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Default Re: High Octane on small engines?

Better late than never,I'll jump in.I'm an old Aircraft Mechanic and am quite familiar with AV-Gas.The LL100(low lead) is just the latest version of aircraft gasoline,the LL100 replaces the former 100/130 fuel,as well as 80/87,it meets the requirements of 100/130,with about half the lead content.There was also a 115/145 grade,and that still be bought in tank truck lots,and can be found at the Reno air races,and at some airports,but not many.The 100 number is the "lean" rating,the 130 number is the "rich" rating,actually the 100 is the MON,or "Motor Octane Rating". The 100LL and 100/130 and 115/145 fuels are made for supercharged engines,I know that 100LL will work fine at 48 in.hg(1.6 atmospheres,24PSI)for 5 minutes ,much above that,115/145 is required,and some of the military or racing engines,also use water injection too.The "slow burning" can be overcome with more spark advance,and richer mixture,and it will bring a return to "lead fouling" ,which some of you younger mechanics may have never seen.As to Ethanol,remember that when using a carburetor,10% Ethanol will lean the mixture 5%,and so on for any mixture of gas/Ethanol,100% Ethanol requires around twice the jet AREA.Pre-ignition and detonation,are both abnormal burning conditions,pre-ignition occurs before the spark plug fires,detonation occurs after the spark plug fires,pre-ignition can cause detonation,but detonation can't cause pre-ignition.
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Old 12-30-2011, 12:16 AM   post #26 of 32
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Default Re: High Octane on small engines?

I agree with what you said Red, and some of the rest of you guys. I recall back in the late 80s before this ethanol laced fuel, using my dad's lawn equipment, he wanted to use premium (91/92) in everything. I kept noticing on a 3.5hp briggs engine on our edger that the plug would have black carbon deposits on it. The carb was perfectly in spec, air filter was clean, etc. It ran just fine, but the plug never had that tan light-brownish color, was always black and carbon covered. I tried using 87 gas in it for a few months and the plug color finally got to where it should be, no longer carbon fouled. This thread reminded me of that. I speculated that it was due to the higher octane fuel either not combusting completely, or just not quick enough since this was a low compression engine. I don't know if it would have harmed the engine, but it was obviously wasteful and didn't have any advantage over using 87. To the OP I would almost say it would be worth it to use the least octane rating you can get away with that doesn't contain ethanol. The damage caused by ethanol fuels seems to me to outweigh the damage that could be caused due to using slightly higher than oem recommended octane ratings.
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Old 12-30-2011, 08:35 AM   post #27 of 32
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Default Re: High Octane on small engines?

Quote:
Originally Posted by JRC0528 View Post
One time I decided to try hi-test in it just to see if it would help out the power/economy/etc. (it had a good set of plugs at the time). The next morning (it was a warm summer morning) when I started it it coughed, sputtered, and died a couple times before it heated up enough to reliably ignite the hi-test; it was behaving as badly or worse than with old plugs on a chilly damp morning!!
I noticed from all of these posts that small things can make a big difference. Timing off, what kind/brand of fuel, amount of ethanol, jetting, water or dirt in the fuel, etc. It's hard to say what is actually making your engine run poorly.
In Red's case, he eliminated a lot of variables when he used his cart to do the testing. The only other thing that might be interesting, would be to make some tuning adjustments with the 91octane to see if the heating problem could be removed.
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Old 12-30-2011, 10:32 AM   post #28 of 32
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Default Re: High Octane on small engines?

After reading the entire thread,I have come to only one answer---Ya'll caused me a **** of headache. Well maybe two--I agree with the statement-Use what the manufacture recomends for fuel.After all,they designed the eng.
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Old 12-30-2011, 10:51 AM   post #29 of 32
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Default Re: High Octane on small engines?

I think all carberated engine dont run as good on ethanol laced gas as theydid on the good old leaded gas we had back before they started selling us oxogenated gas and alcohol laced swill..

..you can re-jet the carbs and fool with the timing on an old engine,it'll help some,but they were meant to have the fuel we ran back then,todays gas just dont cut it in them really...todays cars with EFI and computer controlled injection and timing that can compensate for variations in fuel compositions are a must now,seeing the fuel from one pump to another is often different,as far as how much alcohol actually got added to it...

I read in an old Briggs and Stratton manual that "leaded gasoline of at least 65 octane" is the minimum requrement for satisfactory engine operation...I think one of my old flatheads I had on a go-kart ran better on coleman stove fuel than it did on todays ethanol gas...
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Old 12-30-2011, 11:48 AM   post #30 of 32
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Default Re: High Octane on small engines?

I am also in a slightly confused state. Usually use non-ethynal gas as it is still available in this part of Kansas, but I have been using Startron lately just in case. 87 octane most generally, but sometimes I mix in a high grade. Depends if I get gas in the Truck/Murano at the same time as Mower gas. The delema come from my 317 I just got and the recommendations for it. JD book says 87 and not higher grades. The Kohler engine manual says 87 or higher? JD book says not to use additives like Startron/and or Seafoam. Kohler doesn't say you can't. Anyways I will still use Startron and Seafoam in the JD as I am a firm believer in their use! I have more worries over what Viscosity of Oil to use. I know it says 10w-30 for below 32 degrees but we get those temps, but a few days later it can get and stay above 32 degrees? Sorry, off-topic, I will post that question in another thread.
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