Octane rating for Sportster - Motorcycle Forum
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post #1 of 10 (permalink) Old 09-27-2007, 10:17 PM Thread Starter
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Octane rating for Sportster

For the short time I had my Sportster, I've used 91 octane, because that is what the salesguy recommended that I use and what HD recommends in all their models.

Is 91 octane really necessary? Before I try to fill up on a 89 or an 87 octane, will I experience bad performance if I do? Will it ruin the engine? Will it cause the engine to ping or knock?

There are high-performance sportbikes that require no more than 87 octane, so why should my...Ahem....girly bike 883 Sportster require 91 octane?
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post #2 of 10 (permalink) Old 09-28-2007, 09:06 AM
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Compression ratio, ignition timing and so on all affect octane rating. If it were my bike I would stick to 91 or higher. The higher octane won't hurt anything but going lower than recomended can run you into some problems such as detonation (pinging).

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post #3 of 10 (permalink) Old 09-28-2007, 11:18 AM
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Well, Harleys are not really known for being high compression beasts, is it carbed or fuel injected. My carbureted Evo runs great on 87. I don't know how computerized the newer fuelies are.

I never buy higher octane than I need, just wastes money. Even the wife's turbo Volvo works great on 87, the computer adjusts things so it doesn't detonate, and we haven't noticed any loss in power.
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post #4 of 10 (permalink) Old 10-12-2007, 10:50 PM
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Well, Harleys are not really known for being high compression beasts, is it carbed or fuel injected. My carbureted Evo runs great on 87. I don't know how computerized the newer fuelies are.

I never buy higher octane than I need, just wastes money. Even the wife's turbo Volvo works great on 87, the computer adjusts things so it doesn't detonate, and we haven't noticed any loss in power.
I agree with you. My 01 1200 runs fine on 87 or better for everyday use but if I'm going to be cranking it on I'll put 91 in it now and then. My ultra is the same and runs fine on any. I have had one tank of Citco that I had to put 91 in to keep it from running like sh-t. The compression is low and if the timing is right it should be fine. My friends Buell is a 1200 with 10 to 1 pistons and has to run 91.
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post #5 of 10 (permalink) Old 10-13-2007, 10:14 AM
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My friend's '07 Softtail manual says to use 91 octane only. Might want to check your owner's manual.
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post #6 of 10 (permalink) Old 10-13-2007, 12:07 PM
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My friend's '07 Softtail manual says to use 91 octane only. Might want to check your owner's manual.
I've been riding a sportster since 1970 and just to recheck I looked. My 2001 Sportster service manual part #99484-01 page 1-11 says
Use a good quality leaded or unleaded gasoline 87 pump octane or higher. I agree for top end or hard exceleration, 89 and up works better but mine runs fine for the riding that I do on 87. I mainly ride to work and use it for most of my city riding even getting groceries. I save my $ for good beer and wine. On the same page it also says under oil recommendations to use SAE 60 above 80 degrees. The Harley shops say not to but to use 20/50 from 40 degrees and up. I buy my Fram oil filters at Wal Marts and the Synthetic Mobil 20/50 V twin oil there too. Good luck.
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post #7 of 10 (permalink) Old 10-13-2007, 04:30 PM Thread Starter
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I understand that the owner's manual says to use 91 octane, I just wanted to get some opinions on why it needs 91 octane and if people have found out that you could use a lower octane rating than what the manual says.
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post #8 of 10 (permalink) Old 11-08-2007, 12:04 AM
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Run 91 or at lease 89 if you can get it. My Sporty runs like a dog and has spark knock on 87 in hot weather in Texas.
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post #9 of 10 (permalink) Old 11-16-2007, 03:45 PM
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Originally Posted by Urban Coyote View Post
I understand that the owner's manual says to use 91 octane, I just wanted to get some opinions on why it needs 91 octane and if people have found out that you could use a lower octane rating than what the manual says.
Use what is recommended! Remember, pinging (pre-ignition) whether audible or not is caused by timing, ambient temperature, as well as compression. Pre-ignition is damaging to the engine. So, your choice...pay 'em now or pay 'em a lot more later. Seems an easy choice to me.
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post #10 of 10 (permalink) Old 11-16-2007, 05:11 PM Thread Starter
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Use what is recommended! Remember, pinging (pre-ignition) whether audible or not is caused by timing, ambient temperature, as well as compression. Pre-ignition is damaging to the engine. So, your choice...pay 'em now or pay 'em a lot more later. Seems an easy choice to me.

Since it's mostly hot here year round in AZ, it's probably more wise for me to always use a higher octane.
When considering it's a 4.5 gal tank, I'm only paying about .50 cents more to fill up with 91 octane. I think I can manage that.
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