High octane or no? - Page 10 - Honda CBR500R Forum : CB500F and CB500X Forums
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post #91 of 107 (permalink) Old 05-21-2016, 10:30 PM
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I saw 90 in the owners manual and was always filling with premium (91 in California).
After seeing this thread, I filled with regular (87) and I haven't noticed any difference.
Now I'm saving even more $$!

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post #92 of 107 (permalink) Old 05-21-2016, 10:44 PM
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Originally Posted by Nigel-on-Bass View Post
I saw 90 in the owners manual and was always filling with premium (91 in California).
After seeing this thread, I filled with regular (87) and I haven't noticed any difference.
Now I'm saving even more $$!
The 90 referred to in the OM is RON (research octane number.) The number on the North American pump you're using is AKI (anti-knock index) which is the average of the research and motor octane numbers or (RON+MON)/2. An 87 (AKI) fuel might have a RON of 91 and a MON of 83 (giving a (RON+MON)/2 or 87).

In other words, the 87 you're running meets the minimum 90-RON rating Honda recommends and is has the anti-knock properties you need.
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post #93 of 107 (permalink) Old 05-26-2016, 04:51 PM
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I tried it all and came back to regular 87 with no Ethanol. It seems bike is most happy with regular octane so that's what I would recommend.

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post #94 of 107 (permalink) Old 06-01-2016, 09:58 AM
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Originally Posted by Scoot View Post
I have a lot of friends who put supreme fuel into their civics and other cars and claim that they see better duel mileage and more power. I am very quick to point out that if the vehicle is not designed for higher octane fuel then there is no benefit. The higher octane rating is essentially for higher compression engines where detonation could occur. That being said, as a motorcycle tech, I do only run premium fuel in my bikes, not because of a supposed performance increase, but because in Nova Scotia where I live that is the only way to get ethanol free fuel and I do not want the ethanol to ruin the rubber in my 30+ year old bikes ha-ha.
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I love fuel octane threads

High octane fuel doesn't have any more energy than lower octane fuel does, it's simply more resistant to auto-ignition (i.e. detonation.) While the energy from a spark is enough to light off both low and high octane fuel mixtures, the energy found in the conditions in the far reaches of the chamber during a combustion cycle -- pressure & heat -- isn't enough (all else being equal) to cause higher octane fuels to autoignite; they need the advancing flame front to complete combustion.

If your engine and tune don't produce conditions conducive to detonation under operating conditions where it's most likely then running a high octane fuel is not required. With a relatively low 10.7:1 compression ratio (a CBR600RR has a ratio of 12.2:1...) and what I assume to be a fairly mild tune (relatively rich and a non-aggressive timing curve) the 500 is not a detonation-happy machine.

The manual for the 500 calls for fuel with a RON of 90. MON is usually somewhat lower -- 3, 4 or 5 points numerically -- so averaging them (R+M/2) to get an AKI in the 87-range means you can run "regular".

I tend to agree with what was said earlier about ethanol. Try to find a supplier of ethanol-free gas and worry less about octane. Side story: I have a thing for small gas engines and so seeing lawnmowers at the curb on garbage day elicits a sympathy reaction; if I see one I'm likely to take it to see if it can be fixed (and then sold...) My neighbor had his by the curb so I took it before the scrap-metal scavengers got it.)

Got it into my garage. Oil...check. Fuel in the tank...check. Compression...check. Tried to start it, nothing. It had spark so I figure it wasn't getting fuel. I took the carb off and sure enough nothing came out. Took it apart and found the float bowl caked in a white, flakey residue. The float itself didn't move (it was stuck closed) because of this junk. I cleaned the worst I could out and shot cleaner into the jets and air bleeds, pulled the float off and cleaned the pivot and needle (etc etc), put it back together and it fired right up. I wheeled it back to my neighbor and let him know he didn't need to spent hundreds on a new one and suggested he store the thing for winter with a stabilizer and run ethanol-free gasoline if at all possible.

I don't want that stuff in my bike so in my FZ8 I generally run Shell "V-Power Nitro+" 91 which, in Canada at least, does not contain ethanol.
Great answers and exactly the reason why I go with the high octane ... Shell and Esso up here are (apparently) ethanol-free in their 91s so it's easy for me to remember and access.
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post #95 of 107 (permalink) Old 07-01-2016, 03:04 PM
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Originally Posted by Owlman View Post
Great answers and exactly the reason why I go with the high octane ... Shell and Esso up here are (apparently) ethanol-free in their 91s so it's easy for me to remember and access.
Actually Shell V-Power is ethanol free but Esso isn't

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post #96 of 107 (permalink) Old 08-12-2016, 09:25 AM
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There is no gasoline around here in Eastern VA that is ethanol-free.

I have always run 93 but since the book says 87, I tried running 3 tanks of 87 this past winter and the motor started knocking off idle. That is, at idle when I would give it throttle it would knock then rev up. I also got a very dramatic 10% loss in MPG. First time I have ever seen less than 60 MPG. I went back to 93 and everything cleared up. Then tried 87 again with the same results.

My bike is stock with DanMoto slip-on. It seemed to run fine otherwise but the MPG loss and particularly the knocking was worrisome.

My brother tried the same experiment with his CBR500 (stock with 2-brothers slip-on) and he experienced the exact same thing.

This was in the cold winter with "winter blend" gas though which is crap in the first place. We haven't tried in the summer. Most people might miss the knocking because it's not readily apparent unless you're used to tuning motors.

Now, it could be that both of our bikes have "carbon build-up" from using high octane fuel that now makes it not run correctly and therefore unable to run on 87. This is a topic of debate though. Especially with fuel-injected bikes that are suppose to adjust the timing for the octane used.

2013 CBR500R

Last edited by sprok; 08-12-2016 at 09:34 AM.
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post #97 of 107 (permalink) Old 08-12-2016, 10:16 AM
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Especially with fuel-injected bikes that are suppose to adjust the timing for the octane used.
Please elaborate further, by what means this engine should detect octane rating of fuel to adjust ignition.
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post #98 of 107 (permalink) Old 08-12-2016, 11:23 AM
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Please elaborate further, by what means this engine should detect octane rating of fuel to adjust ignition.
One method is with knock sensor(s). The computer just advances the timing until it knocks then backs off. The sensors are capable of sensing knock well before you can hear it. Advanced timing gives more power (to a point). However, the computer has a number of sensors to determine how well the motor is running and then adjust as needed even without a knock sensor.

That's why it's recommended to disconnect the battery any time you make a change that affects the fuel/air/timing. This will reset the computer so it can start at a baseline then re-tune the setup.

Now whether or not any particular motor can properly handle octane changes depends on the design and firmware. Unfortunately that's something manufacturers don't want us to know anything about so we often don't know how or if it actually works.

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post #99 of 107 (permalink) Old 08-12-2016, 11:53 AM
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One method is with knock sensor(s). The computer just advances the timing until it knocks then backs off. The sensors are capable of sensing knock well before you can hear it. Advanced timing gives more power (to a point). However, the computer has a number of sensors to determine how well the motor is running and then adjust as needed even without a knock sensor.

That's why it's recommended to disconnect the battery any time you make a change that affects the fuel/air/timing. This will reset the computer so it can start at a baseline then re-tune the setup.

Now whether or not any particular motor can properly handle octane changes depends on the design and firmware. Unfortunately that's something manufacturers don't want us to know anything about so we often don't know how or if it actually works.
As en Engineer I'm very well aware how in general an engine manegent can detune (I've yet to see any ECU to detect higher than recommended octane rating) ignition in case it detects knocking. Actually SAAB had run tests with a system what measures ionization of gases after the burning in the cylinder to detect knock.

What I have asked to please explain me by what means THIS specific engine should detect octane rating of fuel to adjust ignition. As to my understanging this (and practically no other) motorcycle engine has a knock sensor installed.
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post #100 of 107 (permalink) Old 08-12-2016, 12:17 PM
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As en Engineer I'm very well aware how in general an engine manegent can detune (I've yet to see any ECU to detect higher than recommended octane rating) ignition in case it detects knocking. Actually SAAB had run tests with a system what measures ionization of gases after the burning in the cylinder to detect knock.

What I have asked to please explain me by what means THIS specific engine should detect octane rating of fuel to adjust ignition. As to my understanging this (and practically no other) motorcycle engine has a knock sensor installed.
Yeah, why not state that in your first post? Where are we going here?

A number of people have asked manufacturers about octane in modern bikes and generally they respond that the system can adapt. I don't have a list handy but quite a few modern motorcycle motors do in fact have a knock sensor of some sort. For example Harley's Delphi fuel injection they specifically state it has some sort of detection system but I'm not sure what it is. The Japanese bikes have had some form or another for decades in racing.

This motor I don't know anything about so I can't say if it does anything but it's not uncommon for modern fuel-injected motors to be able to account for differences in fuel.

But to come back to my original post. My bike ran like crap on 87 so something is going on. Which makes me wonder if this motor DOESN'T handle octane changes. Which was my point of putting that in. That's the debate. Does it do anything or not? I don't know. Do you?

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Last edited by sprok; 08-12-2016 at 12:21 PM.
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