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Well your located in Ohio thats been cool to cold for some time now so your M8 motor isnt running near a hot at it normally does in warmer summer cond which is likely why your getting away with lower octane fuel not detonating.

Another reason you can get away with lower oct fuel is the motor is new not having a chance to build up excessive carbon in combustion chambers yet which can increase compression & also cause localized portions of carbon buildup to get over heated/cherry red both of which can lead to detonation too.

So with low miles with little carbon buildup & cooler temps @ this time your M8 motor happens to be doing ok on lower 89 oct fuel,but after you put approx 6,8,10k miles on it alsong with also riding in significantly warmer 78-80+ deg heat and it will likely be a diff story requiring a min of 91 or maybe even 93 octane fuel to not detonate esp if you ride 2up w-bike loaded in moutains.

BTW,run a full tank of fuel treated with chevron Techron (concentrated version) 2 dose rate of 1.5oz per gal fuel (9.0oz's per 6 gals) thru the motor in a tank of fuel just before you do each oil & filter change.

Doing that will help keep carbon buildup in comb chambers to a minimum also with keeping the motor running nice & smooth too due to keeping the injectors nice & clean too which is a good thing to do.

I do the techron clean to my HD which helps keep it running nice & smooth with crisp throttle response,max fuel mileage & along with also helping to keep it from detonating on HD's rec 91 oct fuel for the 9.2 compression it's got too,even in summer heat riding 2up w-bike loaded.

Scott

 

I run the best gas I can get. Most all the time its 93 no ethanol which is readily available in my area, and cost the same as the crap with ethanol.

As others have said octane does not really make more power. It does help prevent knocking or pinging, which is very destructive for a motor. The hotel the outside temperature the more likely a motor is to ping or knock. The hard you twist the throttle the more likely a motor is to ping or knock. If the motor does have a knock sensor, and it senses knock it will pull some timing out, reducing the performance of the motor.

I do not want to chance one of my bikes pining or knocking. I spend a lot of money on my motorcycles, sure not going to save a little money and risk it.

80% of the time when I am filling my bike I am also filling my wife's bike. We average 25K miles a year. So if you figure you save 30 cents a gallon by using the lower grade, it would save 180 a year per bike. Defiantly not worth it. If you ride less than 25K a year then you would save less.

Just my .02

 

I realize that higher octane doesn't mean more power, but I also wonder if 2 points of grade means a damn thing. You make a good point about the actual cost though. Maybe I'm a little too frugal sometimes lol.

 

Why do people debate this? Just put premium in it like the owners manual states. Even if the difference between mid and premium is $0.50 a gallon, that's only $3 on a dry fill. Are you really that much of a cheapskate???

 

Octane raises the flash point of gas, so it will not pre-detonate. Higher octane fuel has less power than lower octane. (To answer the inevitable question of "so why do race cars use really high octane fuel", 'cause they run really compression engines, and need it to prevent pre-detonation).

Run the lowest octane you can, without engine knock. Remember though, you may not hear knocking/pinging, but still maybe getting it. Also as other poster mentioned, knock sensors will retard timing, and reduce power in the proces.

My opinion, run the 93. The loss of power from the higher octane is minimal, as is the cost. Knocking can cost a lot in the end.

 

I read where in gas stations that only use 1 hose for all 3 grades of gas, if the person before you used regular, and you chose premium, you would wind up with about a gallon of regular before the premium would hit the tank. So if you only needed 2 gallons to fill the tank, you'd be lucky to wind up with mid grade in that purchase, instead of premium.

Seems like almost every station only has 1 hose for all 3 grades of gas.

 

You really don't get it do you? Manual doesn't call for 93, it calls for 91. Which is pretty damn close to 89! And it's not an extra $3 a tank, it's an extra $3 a tank over and over and over and over and over. This bike isn't going anywhere. I'm retired and yeah an extra $6 or $9 bucks a day or more matters to me, especially if it turns out I'm flushing it down the *******. See why we debate it ?

 

No it doesn't! And this was covered in another thread.

 

you're right, it calls for 91, not 89..going out on a limb here and guessing the engineers that developed, designed and tested the engines didn't come up with that rating arbitrarily and had a valid reason because they actually know what they are talking about..go ahead an run 89..you'll be the exception not the rule and you can be a beta tester for us all

 

You make a good point, I get it. Maybe not a great idea on a new engine. You guys here are the Harley experts, not me- it's my first one. That's why I'm asking for opinions. I'm going to say that I'm undecided right now but there's about 4 months of winter left in this frigid hell for a choice to be made. Maybe Ohio is the only state that has 87/89/93? Maybe it makes more sense to just carry some octane booster. Maybe I'll take the advice and run 93.