Octane Observations

#22
I've gone over this subject many times with others who swear higher octane makes their engines run better. It's a waste of money. Now, I completely agree on the ethanol free fuels, but if your engines static compression ratio is 9:1 or less, it isn't doing anything other than making you hope. We can go even higher on static compression numbers when dynamic compression is figured and camshaft duration/overlap are calculated. Read up on inefficient combustion. Also read up on motor rated verses pump rated octanes and who sells the most honest fuels. These are all things I've learned from tuning sessions during our Fastest Street Car Shootout days....
 

SAS289

Well-Known Member
#23
Years ago a guy on youtube was testing what fuel made his clone powered generator run longer. Regular or 93 octane. I don't recall which ran longer but I do recall that the 93 octane made the engine run hotter than the 87.

The Hisun 196's that are on the Coleman 200 bikes has a sticker on the tank that says "90 octane or higher". I wonder what they were smoking when they figured that? The CR on it can't be any higher than 8.5:1. Runs fine on regular 87.
 

Minimichael

Well-Known Member
#25
Wow, all good food for thought. Thanks guys. Thanks for taking the time on this subject. Sometimes reading those old threads from 10 years back can feel kinda lonely ;)
 

SAS289

Well-Known Member
#26
Over the years the only issue I have seen that may be related to ethanol was rust starting in the Hisun 196 engine's gas tank. From that point on I went to extremes by draining the tanks and coating them with oil for off season. All my clone engines get the carb bowls drained and oil coated for off season.

I purposely leave the fuel in the tanks on my small riding mower engines daring the ethanol to do something and it never has. They have started up fine after sitting for months. One was an early 80's 8HP Briggs vertical and the other a 71 6HP Tecumseh vertical.

This past weekend I serviced a 2014 Kohler engine on a push mower. The rust in the carb bowl was unbelievable. Pretty cool little engine with a thermostat mounted on the muffler for the automatic choke.
 

Minimichael

Well-Known Member
#28
Here in tx we have qt stations with 91 octane non ethanol. I was having issues with ethanol softening up the tank sealing epoxies. Not an issue any more.
Oh, now that's news. I have epoxied a couple of tanks and been real happy with them. I hadn't thought about tanks and carbs and the like giving off rust. I guess I was only thinking about the combustion chamber... But even then I expect moisture could get into the crankcase if there's a lot of blow-by pushing past the rings?
 
#29
Ethanol over time softens epoxy it was not rust, the epoxy gets like rubber. Also the tygon lines on the echo blower and string trimmers and chainsaws where the lines get brittle and I would have to change them every couple of years have stopped breaking now that I use the non ethanol. Also the carbs getting full of the green crud has also stopped even when I fail to drain the tanks and a year later the gas will still smell like gas. I did not realize how destructive the ethanol gas was to our small engine stuff.
 
#31
At the risk of sounding like a broken record, I have to say this: Any gas you store/keep in cans for use in those small motors, such as trimmers, mowers, (and yeah, mini bikes,) should be high octane gas. Additionally, it should be kept "treated" with StarTron (the stuff in the blue bottle). Using higher octane gasoline and keeping it treated has made my life a helluvalot easier over the years. I'm sure many of you have read stories of people who had to rebuild carburetors, replace fuel tanks, lines, etc. Never have I ever had to do any of this to any of the many small powered products I own. I'm sure most would agree that many of these problems we read about could obviously be the result of ethanol. That said, I don't really believe the degradation of an already low octane gas serves to help in any way.
I credit having been a New England boat owner for most of life to coming to know how to effectively deal with both low octane gas, and (especially) ethanol enhanced gas. Leaving gas in your boat for 8 months over the winter has a way of teaching you a lesson you might never forget. And once again, using a relatively low octane fuel in your vehicles will generally never pose a problem as it has the ability to electronically compensate for its combustion. Besides, it's cheaper, and it works, right? Unfortunately, most small single cylinder motor applications just aren't that sophisticated.
 
#32
This thread will be just like the "what oil should I run" threads..." Everyone will post what works for them. Comparing STORING fuel to what fuel your engine NEEDS are two very different things. Any fuel that is stored starts to lose its octane rating after 30 days. Ethanol free fuel is a better alternative so long as it meets your engines octane requirements. It is also easier to read on a plug for tuning purposes. Those are facts. There is good advice here from many seasoned members. If people want to dump 100 octane in their 8.7:1 compression ratio engine and say it runs way better, well that is an opinion....
 

Minimichael

Well-Known Member
#33
This thread will be just like the "what oil should I run" threads..." Everyone will post what works for them. Comparing STORING fuel to what fuel your engine NEEDS are two very different things. Any fuel that is stored starts to lose its octane rating after 30 days. Ethanol free fuel is a better alternative so long as it meets your engines octane requirements. It is also easier to read on a plug for tuning purposes. Those are facts. There is good advice here from many seasoned members. If people want to dump 100 octane in their 8.7:1 compression ratio engine and say it runs way better, well that is an opinion....
Thanks guys. This is all good information. And I'm still learning. It has been interesting that I mostly thought I was starting this thread to ask about others' octane experience -- but the conversation kept steering back toward ethanol!
 
#34
This thread will be just like the "what oil should I run" threads..." Everyone will post what works for them. Comparing STORING fuel to what fuel your engine NEEDS are two very different things. Any fuel that is stored starts to lose its octane rating after 30 days. Ethanol free fuel is a better alternative so long as it meets your engines octane requirements. It is also easier to read on a plug for tuning purposes. Those are facts. There is good advice here from many seasoned members. If people want to dump 100 octane in their 8.7:1 compression ratio engine and say it runs way better, well that is an opinion....
 
#35
The highest octane rated gas we normally see at filling stations in either 91 or 93. Here in N.H., the highest I've seen, at most stations, is 93. 100 octane is bordering on what we might consider "racing fuel". Again, burning fuel within a short period of time in your vehicle is one thing; storing it in containers for weeks at a time, for use in these small motors, in quite another.
List of U.S. states by standard octane ratings - Wikipedia
 

Minimichael

Well-Known Member
#36
The highest octane rated gas we normally see at filling stations in either 91 or 93. Here in N.H., the highest I've seen, at most stations, is 93. 100 octane is bordering on what we might consider "racing fuel". Again, burning fuel within a short period of time in your vehicle is one thing; storing it in containers for weeks at a time, for use in these small motors, in quite another.
List of U.S. states by standard octane ratings - Wikipedia
Yep, 91 here in Chicago. I see 93 when I drive to Michigan tho. That's an interesting resource, Sunny. Half the states are 93 while most others are 91. Climate?
 

f4radar

Well-Known Member
#37
Ok I read this on the internet so it must be true or the Disinformation Governance Board would have shut the site down
"
The higher the octane, the more energy required to fully ignite a charge. Energy comes from the spark (ignition) and pressure (compression).

In an oversimplified explanation, motors have recommended octanes based on how much compression they produce in the cylinder. If you run a higher octane fuel (which requires a higher pressure input to fully combust), there will typically be unburnt fuel in each charge. That unburnt fuel is more likely to, for lack of a better word, smolder and burnt less cleanly, producing by-products like carbon buildup. "
 
#38
What? No! I would contact the "Disinformation Governance Board" immediately. (ha) My turbocharged Mercedes aside, the 2015 access cab Tacoma we have has the 24 Valve VV-i engine which is listed as having 10.4:1 compression ratio. It loves that 93 I feed it; especially when I'm towing my small trailer boat, or my aluminum dump trailer. This aside, I'd have to simply say that you should buy whatever fuel you believe works for you.
Funny, but I have to laugh whenever this subject comes up as I oftentimes tell people: "Interstate Route 93 runs through my town, and Octane 93 runs through my motors." (ha) Finally, as Forrest Gump once said: That's All I Have To Say About That- Forrest Gump Quote - YouTube
 
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SAS289

Well-Known Member
#39
This thread certainly got me interested again in getting some ethanol free gas.

And with the 91 octane I'll be doing 60......... Just kidding.
 
#40
Ok I read this on the internet so it must be true or the Disinformation Governance Board would have shut the site down
"
The higher the octane, the more energy required to fully ignite a charge. Energy comes from the spark (ignition) and pressure (compression).

In an oversimplified explanation, motors have recommended octanes based on how much compression they produce in the cylinder. If you run a higher octane fuel (which requires a higher pressure input to fully combust), there will typically be unburnt fuel in each charge. That unburnt fuel is more likely to, for lack of a better word, smolder and burnt less cleanly, producing by-products like carbon buildup. "
This is inefficient combustion and is 100% true....
 
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