Quote:
Originally Posted by waterdog
Hey Glider,
How long have you been using 91 octane, in what bikes, and how do they run with it?
I've only been using 93 in my Heritage, usually Shell, since I bought it in April, but have thought about trying 91 in it and see how it runs.
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I've been running the 91 for a few years now, but have noticed in the colder temps that 93 sometimes is needed because of a very slight ping on any hard acceleration, only at times like entering a parkway. It's only ocasional this happens.
Seems just opposite of what is needed but the higher octane really does nothing for performance if it isn't needed to keep any pinging down, just costs more. You can try the 91 and see if you get any pinging and if you do go back to the 93.
There's many factors involved in the right octane for the different bikes that will make a difference. Compression ratios are the first as well as other factors. The lower compression ratios of the stock Harley's doesn't really require the 93 octane.
The only other factor here is the gas is usually sub standard now as compared to years back when you could get 103 sunoco gas. I believe that the method of grading gas now is the RON or research octane rating which I feel is grading it a bit lower than it really is as verified by the eagerness of the modern cars to ping on the lower grades. Of course this is helped along with the smog equipment on most cars today.
One thing to consider when you choose to go to a lower octane is that if your engine pings enough from the 91 that the ECM will pull back the timing to eliminate it through the ION sensing system. This will decrease performance (power) to a small degree and may offset the advantage of goint to a lower grade of fuel. Either way, I feel it's safe to run the 91 and see what you get out of it.