ThrottleX Blog
Monday, August 18, 2014
Can You Use 87 Octane Gas in a Harley-Davidson?
Many Harley-Davidson owners have asked if they can use 87 octane gas in their motorcycles.
Harley-Davidson advises owners of all fuel-injected models to use premium unleaded gasoline. But is it really necessary to use 91 or 92 octane gas?
For starters, there are still some gas stations in the remote areas of the United States and Canada that sell only 87 octane and diesel. Those who’ve ridden their motorcycles along the Alaska Highway through British Columbia and Yukon know first hand that many stations only carry 87 octane. What then?
Generally speaking, if your motorcycle is equipped with a high compression engine, you should run high octane gasoline. What is considered high compression? There is no official standard, but most motorcycle riders consider a ratio of 10:1 or higher as “high compression”.
For sake of argument here are compression ratios on various 2014 Harley-Davidson engines…
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- 1247cc Revolution: 11.5:1
Generally speaking, you should be safe to run 87 octane on a 103ci Twin Cam Harley because its compression ratio is less than 10:1. But with the 1200cc Evolution and the 1247cc Revolution, use high octane.
So why does Harley-Davidson advise all of its fuel-injected motorcycle owners to use high octane fuel? Mostly to stop owners from bringing their bikes into the dealership for pinging. Many of these bikes are still under warranty, and it costs Harley a lot of time and money to fix something that a simple fill-up with 91 octane would have prevented.
Gasoline itself is actually a blend of several different gases and additives. When it’s compressed high enough, it will spontaneously ignite, even without a spark. Octane, however, has a very high compression tolerance. Thus, the more octane you add to gasoline, the more it withstands combustion. This allows the spark plug to ignite the fuel mixture at the precise time, thus maximizing efficiency.
The pinging is caused when compression ignites the fuel mixture before the spark plug does. Using higher octane fuel will reduce premature combustion.
It still varies from engine to engine, however. Many Harley owners have ran 87 octane in their Twin Cam bikes without pinging, and have gotten a lot of years out of their motorcycles. But some have had to stick with higher octane to keep it humming smoothly.
If you want to take advantage of the lower cost of 87 octane gas in your Twin Cam, try using a couple of tank fulls and play it by ear.
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