WILL GUY I have 06 SCREMIN EAGLE 103 FAT BOY and my service manual states do not burnLESS than 91octane, and I allways use 93 octane! MY bike would run like CHIT if I dare put the cheap low grade gas in it, and ALL HARLEYS are supposed to burn at least 91 OCTANE, but I'M sure some body is going to come out and say they only burn the cheapest gas and get 60 miles per gallon, never fails, I love my bike and do not like the thought of being cheap and use regular gas and as for the diesel I do not know, or care to know its rating, because I will never drive a diesel un-less its a R.V. or 18 wheeler. Just trying to help a brother!! PURPLE HAZE.

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With my limited knowledge...

Most vehicles that require a high octane fuel is due to the engine compression ratio. The higher octane fuels do not ignite as easily as lower octane fuel. With a higher compression engine and lower octane fuel you can wind up with predetonation, knock and ping.

Higher octane fuel in a lower octane rated engine is not beneficial at all, actually can make the engine run hotter than usual, not much mind you.

Harley engines require 91 or better because of the heat associated with the engine. Being air cooled the engines are prone to hot spots and can cause problems igniting fuel early. Higher octane fuel works better with the heat and fires off when it's supposed to.

This is just from my research and educated opinion. There are alot of opinions about octane and always putting "good" gas in a vehicle. I had a Honda 919 sport bike and was surprised to read that it took 87 octane. Had a 2005 Dodge Ram 1500 with an owners manual that said 87 is fine but 89 for best performance, didn't notice a bit of difference.

I do think that engine temp is a big factor in performance and octane. That Ram with the Hemi probably would have run better with 87 octane vs. 89 in Chicago during the winter because of the cold.

This goes back to what happened with my bike, the diesel contamination would run like absolute crap until the engine got up to normal operating temperature. Once it was hot it wasn't so much of a deal.

As fare as I have read, there is no reason to stray from manufacturers recommendations unless you go after market and start increasing compression ration.

If you have info supporting or contrary to what I put here please fill me in (add links if you have them, I'm always ready to learn).

 

Yep....thats Y they put the rev limiter on-m>>

 

Diesel has LOWER octane rating. gotta be more volitile to be able to be ignited by compression alone. As everyone else has stated, should be fine after a few tanks of the good stuff!