Gasoline question
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Stage I
Joined: Feb 2017
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From: Pearl, MS
Gasoline question
Since the compression ratio of a 103 engine is only 9.6:1, why does the manual call for premium (91 octane) gas? There are engines all over the world with that ratio running happily on 87 octane.
Extreme HDF Member
Joined: Sep 2010
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From: Phoenix '53, '88, '09 Big Twins
the heat of the combustion chamber, the higher octane resists preignition.
twincooled models do run higher compression, the combustion chamber temps are more controlled and that allows more cam higher compression, and resulting more power.
welcome to the forums!
Mike
twincooled models do run higher compression, the combustion chamber temps are more controlled and that allows more cam higher compression, and resulting more power.
welcome to the forums!
Mike
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From: Honah Lee
It will probably fine if you drive it easy and reasonable. Few do a manual transmission. That means downshifting to keep rpm in an efficient range rather then nailing the throttle in too high a gear. Now if you happen to be in hot rolling interstate and hit grades, that would be pretty lame and in these conditions, most any manual shift in that compression range would need a premium octane grade fuel. Remember, there is no more power in it over 87 octane. Just additives to slow the flash point down so it does not explode too quickly and rattle the engine.
Mine is not a 103 but calls for premium and is a touch higher compression and I can run regular. I just usually just throw mid-grade in it but I have never heard it ping on regular. I have never seen any sign of preignition on the plugs. I have never see a Harley that does not call for less then premimum
Mine is not a 103 but calls for premium and is a touch higher compression and I can run regular. I just usually just throw mid-grade in it but I have never heard it ping on regular. I have never seen any sign of preignition on the plugs. I have never see a Harley that does not call for less then premimum
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From: South Carolina
Jump off the soap box, the guy asked a legitimate question.
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From: Doghouse... mostly
Try running your bike on a few tankfuls of 87 Octane. If you think your bike runs okay on it, continue to use it. There are many folks on here that use 87 and have had no issues with their bikes at all. It's your bike after all.
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From: Alberta Canada & PV Arizona
Exactly what I was thinking!
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The bikes need 91 and that is that. Some times all you can get is the 93 blend stuff it will do. They sure do not need any higher than 91/93. Nor will it make the bike any faster running higher.
Not worth the long term risks of running 87/89 in them. My older 96 EVO calls for 87 runs fine on it.
The only thing that makes any real difference is 10% blend or not. And then it just comes down to the straight gas just gives a little better fuel mileage.
Not worth the long term risks of running 87/89 in them. My older 96 EVO calls for 87 runs fine on it.
The only thing that makes any real difference is 10% blend or not. And then it just comes down to the straight gas just gives a little better fuel mileage.