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Old 08-27-2017, 03:45 PM   #41
Senior Member
Brand: Still Looking
State: Texas
Posts: 4,690
THOR #2121
Higher Octane rating increases self-ignition temperature and thus reduces knock/detonation, but it won't affect flame speed (once spark ignites fuel mixture) enough to matter. Below is a summary that basically says the same as my old Internal Combustion Engines textbook.

Keep in mind that motorhome and generator engines operate at relatively slow RPMs compared to racing engines, so fuel mixture flame speed is likely even less important.

Whitfield Oil Company Flame Speed, Octane Number & Horsepower


The octane number of a gasoline has little to do with how fast it burns or how much power the engine will make. Octane number is the resistance to detonation. If the octane number is high enough to prevent detonation, there is no need to use a higher octane gasoline since the engine will not make any additional power. Octane number is not related to flame (burn) speed either. Variations in octane quality are independent of flame speed. There are some high octane gasolines in the marketplace with fast flame speeds and some with slow flame speeds. It depends on how they are put together. We prefer fast flame speeds because we know that a properly tuned engine will make more power on this type of gasoline than one that has a slower flame speed.

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Old 08-27-2017, 04:18 PM   #42
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Brand: Thor Motor Coach
Model: S.O.B.
State: California
Posts: 1,357
THOR #3483
Originally Posted by SuperD View Post
Actually high octane in a low compression engine will hurt. High octane burns slower and the engine can't develop full power.
Yes, Dave, that was what the guy at the Paint Dept. was trying to get across to me. The discussion is not about anything other than what high octane does to a generator not the Ford V-10.

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Old 08-27-2017, 05:30 PM   #43
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Brand: Thor Motor Coach
Model: outlaw 37ls
State: Europe
Posts: 230
THOR #6831
as a rule low grade is ok, 10% alcohol max, but in some western and mid west, alcohol free gas can be found, it is usually premium. after a few tanks the engine control will adjust and there will be a mot more power, the alcohol really waters the gas down.

now for moutian driving ( especially colorado) i will begin to switch to premium as low grade gas will run ( colorado gas has a lot of EPA additives) that drive up cylinder temp. causing much hotter running engine which can be a problem when having heavy loads in summer temp.

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