Never bought it and don't think its needed for the Harley. I buy the premium gas with the highest Octane rating.

 

Same here and not any problems to note yet.

 

None! I run 89 for years now in all my bikes. No issues at all.

 

As an engineer (specifically in refineries) and long time Harley rider I am fascinated by the variety of responses all over the spectrum of octane and gasoline and how it affects knock. From a strictly technical perspective octane rating has nothing to do with energy content, mileage, or performance. Octane number is just a measure of knock resistance. Its based on a comparison performed in a standard one cylinder test engine with the burning of isooctane and n-heptane. Isooctane is rated 100 and produces relatively knock free operation while n-heptane is rated 0 and produces violent knocking. A knock rating of 70 is comparable to a mixture of 70 percent isooctane and 30 percent n-heptane. Refineries control the knock rating of gasoline with additives similar to the octane boosters you can buy over the counter. It is true that compounds such as acetone or xylene can also increase knock rating. This is all interesting mumbo jumbo when it comes to our bike engines. To make matters more interesting all brands of gasoline come from the nearest refinery in most cases. Here in the Rocky Mountain west we have 3 or 4 refineries. I would be willing to wager that every drop of gas in Denver comes from no more than two refineries. One is Suncor and the other is Valero. A lot of the gas all over the country is mixed in pipelines and delivered from terminals to each outlet.

From a practical perspective you should buy any brand of gas you like. They are all almost identical. Buy whatever the highest octane they have. Again in the Rocky Mountain west it is 91. You can use the lowest octane gas that produces acceptable knock performance in your engine. If you put 87 in your tank and it doesn't knock under all ranges of operating conditions you are fine. Personally I just buy the highest rating of whatever brand of station I am in.

I never experienced much knock in my EVO. Now that I have the stock 103 its noticeable due to the higher compression ratio, I believe. In other words the knock rating of the gas I buy is now more important than it used to be. To be sure, air fuel ratios, compression ratios, driving conditions, ambient temperatures all have an impact on knocking. I am going to try some octane booster and see if it makes a difference. I am also going to see what happens under a lot of driving conditions. I am also going to look at tuning and how that affects knocking. Most of all I am going to ride and enjoy the last of summer and fall. I will be glad to report back on the outcome.

 

K. In order for those boost in a bottle to actually make a difference in octane you would have to use so much it wouldn't be cost effective.
When they say it raises octane levels 6 points,they mean 6 points after the decimal.
Get good fuel. If it's not available then buy a name brand if possible. The gumout stuff gets good grades over at the bob is the oil guy forum,as does torco

 

Unless you've got a radical build you shouldn't be using it either....just saying.

 

its snake oil. I've run 87 octane since day 1 on my current bike.

 

Make your own booster: http://www.best-chemical.com/racing.htm

 

Owners manual on my 2011 FLHTK says NOT to use it as engine damage may result. I use 87 almost exclusively with no ping or knock and will until something happens. 22K and counting. My engine is stock inside and will stay that way.