Not only do you smell a birthday cake but my wife is taking me to the Olive Garden in Fredericksburg. Thanks cHarley.

 

Here's 40 or more posts on a fuel topic and only one guy addresses the most important issue - Ethanol.

I rebuild carburetors for a living and see the effects of Ethanol on older fuel systems every day. We typically tell people that using cheap fuel is a false economy - you'll save pennies now but spend dollars later.

I use Premium Non-Ethanol in everything - EFI and carbureted (especially!) bikes, boats, jet skis, outboards, cars, trucks, saws, and anything else that goes pop!

It typically comes in a dedicated pump so mixing isn't an issue.

 

Octane is a rating to describe the heat resistance, ignition point, of gasoline. Not how much energy it contains, or how much power it will produce. Higher octane gas will not pre detonate in a high compression engine as it takes a higher temperature to ignite it. On the other hand it may cause fouling in an engine designed for low octane gas. Since Harley engines are low compression, you'll get better performance with 87 octane (unless otherwise specified by manufacturer due to heat or hot spots in the combustion chamber). Use the octane level recommended in the owners manual. Using higher octane gas than recommended is just a waste of money. The fuel system in a modern gas engine is resistant to the effects of ethanol. Ethanol can destroy old rubber seals and hoses in an older fuel systems. This is an issue for older engines only though. Ethanol is frequently used as an octane enhancer since it has a higher ignition point.

 

Compression ratio is not the be-all and end-all of octane requirements. Head temperatures, specific hot spots in the combustion chamber as a result of the chamber's shape and materials, the richness of the fuel mixture, and the ignition timing map all play a role.

All EFI Sportsters, regardless of 1200 or 883, require 91 octane fuel. This is likely largely due to the spark timing and to the fact that the heads on air-cooled engines run hotter and therefore require higher octane fuel even at what would otherwise be considered low compression ratios. Since new emissions laws prevent simply running richer to cool the intake charge and reduce the octane requirement, even the relatively low 8.9:1 compression ratio of the EFI 883 bikes requires 91 octane fuel.

Contrariwise, the engine in a 2005-2010 Ford Mustang had an engine with a 9.8:1 compression ratio but only needed 87 octane fuel because of very close attention to cylinder head and combustion chamber design which tightly controlled head temperatures and avoided hot spots in the combustion chamber.

It's simply not possible to just look at a static compression ratio number and tell what octane level an engine needs.

 

Tony, I cal tell you for a fact that 87 will not work in my 2007 1200, I was in Richmond, Va. a few years with a riding friend and was talking to him instead of paying attention and put 3 gallons of 87 in my tank. I could hardly launch in low gear. When I got on 95 north I had to drop into 4th gear even on the slightest grade to keep it from hammering and sounding like it was blowing a head gasket. I was so glad when I got near home and could put some 93 in it. As to the 87, I have a friend with a 2009 883-C who runs 87 and has no problem.

 

Stock form octane that's may or may not work from one bike to another is one thing. When you spend your time v tuning , or get a dyno tune, the higher octane will be needed if you make any timing advancements. Plus you want to run what you tuned with. Running a higher octance no matter what isn't hurting anything with pump gas no matter carb or efi. If your a cheap *** or just don't care what you run then by all means do what floats your boat. The 2007 sportster manual states whether 883 with 8.9:1 or 1200 9.7:1 to run 91 octane. It also states blends can be ran but personal preference and longterm stability of fuel will out weigh running a blend.

 

Yes, my 2007 883 uses 91+.

 

Here's my bike at my favorite local pump...