Did not know that CA limited gas to 91. At least one good thing about IL, and there are not a lot of them, is that you can get 93 Octane gas.

 

For the most part 91 octane is as good as you're gonna get in CA. There are some places that have 100 octane at the pump, but it's pretty expensive. Last time I filled with 100, it was $8.99/gal.

I like running a tank of 100 octane in my Harleys every so often. Both my bikes are high compression builds, so the engines really love it.

 

Mine definately seems to cold start better on 97 than 91...

 

I ran 93 in my Sporty but have been running 91 in the Dyna. The local Southern States just started carrying ethanol free 87 so I filled it with that yesterday. I'm a half tank down so far and haven't seen or heard anything disturbing yet.

 

For 10 years on every HD motor from the 750 though 110's I have run 87 octane without a single issue. Well not exactly I get better mpg's even the CVO 110's yield 50 mpg on E10 87.
Again 883's, 1200's 88's, 96', 103's, 103 HO's, and 110's. I currently have a 120R that when I get 3K on it (at 1,500 now) I am going to ease from 93 down to 91 then 89 and if it responds well I will try 87.

I do make sure that all have iridium plugs, learned not to lug an engine in the 50's and all with oil coolers and keep the cylinders clean with Techron. I ride the bikes collectively over 30K a year. When I traded my 10 Ultra with 32K on it the tech that test rode it said it was the strongest running stock Ultra that he ever tested.

Use what you want but I am more than pleased with the performance of each of the bikes over the years. that is what I ran in my Vettes and Viper for years also with absolutely no ill effect.

And yes a high compression built with radical cams needs high octane and cooper core plugs to run the best. I avoided the 12.5 to 1 compression build for the 120R and went with 10.5 to 1 just to be more streetable and use a lower octane of gas. My run in is one where the engine is worn in over a 3,000 mile process. That will result in a stronger running engine ultimately than the hard break in. Takes longer but well worth it.

By the way the true easier starting is provided by lower octane. Octane is a measurement of the fuels resistance to ignition. Therefore the higher the octane it STARTS HARDER! The other unusual result of lower octane is when used correctly it produces more power by virtue of the fact that it burns more completely in the combustion cycle. All gas (in the summer) is 115,000 BTU's. So if more gets burned in the cycle the more power is produced. The higher the octane the more that goes out the exhaust. 1 HP is about 5,000 BTU's if my memory serves me right.

BMW to achieve higher mpg with the 6 cylinder bike that they came out with a few years back went to a very long stroke to give the fuel more time to burn. They had a goal of 40 mpg on that monster motor and they got it.

 

You are correct about the burn rate of the lower octane being faster than the higher octane.
This is where the pinging comes from with an engine set up to burn the higher octane. With a timing setting set retarded much more that it would be with a higher octane, you can successfully burn the faster burning fuel.
While doing so you also produce less torque & horsepower from the retarded timing. If you are burning a high octane fuel you can advance the timing as to start burning the fuel at a much earlier point in the compression cycle. This allows you to complete the burn correctly.
Just as in race cars burning alcohol for fuel in place of gasoline. The alcohol burns much slower than high octane gas. Not as many BTU's, but you can put a lot more fuel in & advance the heck out of the timing. It also needs a different cam to perform right. Also higher compression, & create more horsepower.
Over simplification I know. But bottom line is that you can produce higher performance with higher octane fuel if the engine is designed to do just that. If you are happy with a lesser performing engine,,,,, Go ahead & let the ECM d-tune everything to keep from pining. Or you can do it yourself.
Keep in mind the driving style also enters into the equation. Also have you ever seen what happens to the piston with pre-detonation ?? Not worth the taking chances.
If your theory was true,,, I wonder why high performance aircraft air cooled engines use 110/130 octane rather than 87 octane. Wouldn't they make better horsepower ??

 

Nothing but 93 in my bikes.

 

sloufoot: If the engine knocks the sensor detects it and retards the ignition for a short period. No detonation no retarding.

Stock HD engines are not high compression they are over square low compression mild tuned engines. Keep the compression chamber free of build up, rev the engine through the gears and use oil coolers and all that will allow the engine to perform.

Our nanny government requires that vehicles sold to run on the public highways MUST be able to run on 87 octane. That is why the knock sensors exist. Also they have initiated studies and discussions with the goal of reducing av gas to 87 because some are getting it and using on the streets.

You must have missed that my set ups on over 20 HD's in the past ten years out perform stock bikes.

 

On a somewhat related note...

https://www.harley-davidson.com/cont...rs-manual.html

 

In my opinion, Harley says to run premium and since they made the bike, I'm pretty sure they know what they are talking about. I used to have a 2001 1200 sportster that would ping like crazy on regular gas, a little less on mid grade and no pinging on premium. The way I look at it, even if premium was .50 cents more than regular and you have a 5 gallon tank, that's only $2.50 more to run premium. If you are worried about an extra $2.50 to fill up, you should just sell your bike and buy a prius.