FUEL OCTANE vs. ENGINE PERFORMANCE - Kawasaki KLR 650 Forum
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post #1 of 19 Old 11-04-2013, 04:22 PM Thread Starter
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Question FUEL OCTANE vs. ENGINE PERFORMANCE

Would one of you smart guys explain (in simple terms) the deal about regular vs. Premium gas and how each grade of fuel impacts various types of engines.
I REALLY appreciate it!!!!!

~Things work out best for those that make the best of the way things work out~
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post #2 of 19 Old 11-04-2013, 05:24 PM
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My simple understanding is this. The higher the octane rating the slower the burn/volatility. High compression ratios need a slower burning fuel so as not to detonate, that is, to combust before the spark plug fires.

Now, someone much smarter than me needs to comment.............

Gray-haired riders donít get that way from pure luck.

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post #3 of 19 Old 11-04-2013, 05:53 PM
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A higher compression engine needs a higher octane. Higher octane gas is *less* volatile than low octane and it takes more heat/pressure to ignite. The reason you would want this in your high compression engine is because as the compression builds but before the spark, low octane gas can ignite prematurely and cause knocking or pinging. An engine with 10:1 or higher is likely to want high octane.

Lower octane gas is just fine for most engines. And my KLR.
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post #4 of 19 Old 11-04-2013, 06:07 PM
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post #5 of 19 Old 11-04-2013, 06:53 PM
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Oh sure, trump us with your huge wiki. The rest of us kept our wiki in our pants for this one.
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post #6 of 19 Old 11-05-2013, 12:15 AM
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Here is my understanding:

Higher octane fuel has a higher, or hotter, flash point. Higher compression motors compress the fuel/air mixture tighter and that in turn "heats up" the mixture. Sometimes the heat is enough to make it ignite before it's supposed to. When this happens a ping can be heard in the engine which is commonly referred to as pre-detonation. As far as a "cleaner" or "higher quality" of fuel I've heard mixed reports but most say it's not. I have run both low octane and high octane with zero noticable difference between the two. Also I have never heard my engine ping. Therefore, I run low octane other than the dead of winter when it takes me a while to go through a tank of gas. In the winter I buy non-ethanal fuel which is only available here in the premium, high-octane grade.
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post #7 of 19 Old 11-05-2013, 01:29 PM Thread Starter
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Thanks for the help--I get the concept, now I just need to learn a bit more about compression..

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post #8 of 19 Old 11-05-2013, 02:31 PM
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This is a great video that explains it more. This guy has a lot of really good info on motorcycles in general.

http://m.youtube.com/watch?p=PLyLD4Y...&v=pLPSY0rzMZo
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post #9 of 19 Old 11-05-2013, 03:40 PM
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Quote:
Originally Posted by kyxon View Post
This is a great video that explains it more. This guy has a lot of really good info on motorcycles in general.
Very informative! I'll keep with the 87 octane in my 9.5:1 KLR.
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post #10 of 19 Old 11-05-2013, 06:47 PM
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Quote:
Originally Posted by kyxon View Post
This is a great video that explains it more. This guy has a lot of really good info on motorcycles in general.

http://m.youtube.com/watch?p=PLyLD4Y...&v=pLPSY0rzMZo

That was hard to watch but he did make some good basic points and got me to thinking of the terminology I used earlier....ĒHigh compression ratios need a slower burning fuel so as not to detonate, that is, to combust before the spark plug fires.Ē That would be pre-ignition to be correct. What the guy is describing in the youtube vid is detonation.

Another thing not mentioned in the vid was ethanol blended fuels and how that affects octane ratings. Seems that ethanol can be added to a lower octane gasoline to increase its octane rating which is fine in the short term but can actually lower the octane rating once the fuel has time to absorb moisture and phase separate.

This happened to me on another bike that has an 11.5 :1 compression ratio and is fuel injected. The base problem was running contaminated fuel that blocked the MAP sensors. That problem solved I now run pure premium gas in that bike and easily available E-10 regular 87 in the KLR with the addition of either Sta-Bil or Sea Foam in both as a preventive measure as both can sit for long periods.

Gray-haired riders donít get that way from pure luck.

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