Is it my imagination? (Octane...)

[holligl]

I normally use 91 octane, but recently refilled with 93. It's probably my imagination, but I swear it feels quicker. Any one see a marked difference with better fuel?

 

[hobdayd]

I always use Super over here in the UK. I think it is 97/98 vs. standard 95. There are many claims that the higher octane fuel increases economy and power.

I just sense the bike runs better on the Super.

 

[Nikolajsen]

I always use 95 octane. Never tried lower than 95.
In the manual it says "Premium"...dont know what octane that is....

 

[Terminus]

I am not 100% positive but I think in the owner's manual it says to not use anything lower than 91 octane. That is for bikes in the US anyway. I am not sure if the octane ratings are the same for the UK and other places? I see some guys referencing 98 octane. Typically I think that is close to racing fuel over here. Maybe I am missing out..... ::26::

 

[WJBertrand]

The Research Octane Number (RON) rating is used in most of Europe. There is also a rating method called Motor Octane Number (MON), that will always return a smaller number than RON. These are different test methods to determine Octane. In the US we use an average of RON & MON to arrive at the POM, or Pump Octane Number. This will always be lower than RON, even for the same exact fuel.

Regular grade fuel usually has more energy per gallon than premium so as long as your engine doesn't suffer knocking, there's no advantage going to premium. Many engines have knock sensors that will retard the ignition if knocking is detected and one will never hear the knocking. In such cases using premium will allow more ignition advance and better performance. So what you feel in that case is the different tuning, not the fuel necessarily. I don't think the Super Ténéré has a knock protection system with sensors however. Any difference in feel between fuels is probably placebo effect.


Sent from my iPhone using Tapatalk Pro

 

[Buelligan]

I live in the desert southwest, where it's hard to find octane around 91, let alone higher.
Recently I took a trip back east and was able to find +93 Octane, I did notice an improvement in gas mileage and performance.
It was nice, shame I can't find gas like that back home :'(

 

[Nissbird]

The USA supplied 100 octane to the RAF in 1940 and this gave a substantial increase in power, so much so the Luftwaffe noticed the change in performance of the Spitfires and Hurricanes in the Battle of Britain from the earlier conflict of the Battle of France.

 

[Sierra1]

It was my understanding that "premium" fuel had a hotter spark; bigger bang. That is why the higher the engine compression, the higher the octane has to be. The Tenere is 11.0:1 compression. Not crazy high, but that is why the manual specifies 91 octane. I do know that the higher the temperature, combined with a heavy load, and going up steep hills requires higher octane than regular.

 

[Terminus]

The USA supplied 100 octane to the RAF in 1940 and this gave a substantial increase in power, so much so the Luftwaffe noticed the change in performance of the Spitfires and Hurricanes in the Battle of Britain from the earlier conflict of the Battle of France.

Yeah, I think that is aviation fuel when you get to octane ratings that high. Here is a follow up question that I hope does not derail this thread, but I wonder what the maximum octane you can run in our bikes without causing damage is? Or is there such a thing is too much octane? More of an academic question more than anything.

 

[Eville Rich]

Using nonscientific terms, the octane rating describes how quickly or "explosively" the fuel will burn. Lower octane is "more explosive," or "less controlled," while higher octane fuel burns in a little more of a controlled and slower fashion.

For higher compression motors or motors with turbos, the controlled burn is important. It allows for advancing the ignition timing and optimizing the spark relative to piston position. If you have high compression and a relatively advanced spark, the less controlled burn of a lower octane fuel can lead to engine knock/ping. This is most apparent when under high loads and temperatures. For a turbo engine, you may have fairly low compression at atmospheric pressure, but spin up the turbo and it's like increasing your compression ratio. For cars with knock sensors, these detect the pre-detonation of fuel (ping/knock) and allow the ECU to retard ignition timing. That's why you often get worse performance with lower octane fuel in a higher compression or turbo engine - the ECU is protecting the engine by retarding the ignition timing.

I typically run 91 octane from my local gas station - no issues at all, but I'm also not in the extreme heat of the desert SW or climbing mountains. 93 octane doesn't seem to make much difference when I do get it. I have a local gas station with 110 octane racing fuel. I haven't tried that yet ($6/gallon) but I suspect nothing bad would happen, other than potentially getting some combustion by-products that would otherwise get burned up with proper combustion (e.g. more CO rather than CO2). Might mess up a catalytic converter a bit. But there would be no benefit to the higher octane unless I could advance the ignition timing, which also relates to the underlying fueling and ignition system being designed to take advantage of it. For a race engine, those are run at the ragged edge, so they can be designed for higher octane - higher compression or boost and tightly controlled ignition advance.

Eville Rich
2016 S10
2015 WR250R

 

[Checkswrecks]

Yeah, I think that is aviation fuel when you get to octane ratings that high. Here is a follow up question that I hope does not derail this thread, but I wonder what the maximum octane you can run in our bikes without causing damage is? Or is there such a thing is too much octane? More of an academic question more than anything.

Diesel and Jetfuel are much higher octane than pump gas and you sure don't want to try those, so yes, there is definitely a limit. The next highest would be aviation 130 and then 100LL and each of those (comparatively) have a lot of lead which will foul a motorcycle engine. Also not good.

Octane is a definition of how much you can compress the mixture before autoignition happens. Because you can't change the compression ratio in these engines, what you buy from the pump is about the best you'll be able to do. If you were to add a LOT of octane booster (or diesel fuel), you'd waste the money spent to buy it, till getting to the point that problems arise because the mixture is so far off that the gasoline doesn't want to burn smoothly.

 

[fredz43]

As for improved MPG, I live in IL where all our gas has 10% ethanol. When I travel to several eastern and southern states, I frequently find non ethanol fuel and that results in better MPG. I almost always run premium, so the difference is in non ethanol, not in octane.

 

[Dogdaze]

I think you would have to run several tanks of high octane to feel any significant improvement on performance, locally I can get 120 RON, for track cars, I would have to run at least 3-4 tanks before there would be an actual difference. Would I buy the stuff, nah, not likely!

 

[Checkswrecks]

I think you would have to run several tanks of high octane to feel any significant improvement on performance, locally I can get 120 RON, for track cars, I would have to run at least 3-4 tanks before there would be an actual difference. Would I buy the stuff, nah, not likely!

Yeah, but you're a Euro-Dog. We can't even buy that stuff in the US.

 

[Nikolajsen]

In manual for my 2017 S10 (probaly the same for all, but at least from 2014.

 

[Dogdaze]

Yeah, but you're a Euro-Dog. We can't even buy that stuff in the US.

CW, and at $3.50 a litre would you want to?

 

[Sierra1]

As for improved MPG, I live in IL where all our gas has 10% ethanol. When I travel to several eastern and southern states, I frequently find non ethanol fuel and that results in better MPG. I almost always run premium, so the difference is in non ethanol, not in octane.

Generally, premium/91 octane, has less ethanol than regular. And, yes, I observed the same decrease in mileage when I had to switch to the ethanol blend. It was 2-3 m.p.g. in my truck; likely a more drastic difference in a bike. Made the switch to TruFuel years ago in my small engine stuff.

 

[Checkswrecks]

CW, and at $3.50 a litre would you want to?

Touche'
::003::

 

[EricV]

Eville Rich gave a very nice description. Put another way, higher octane fuels have a greater resistance to pre-ignition. Low octane gas is sort of like paper. Ignites easy, burns hot and fast. High octane is more akin to cardboard, takes a bit more heat to ignite, burns hot and burns longer. Resistance to pre-ignition, (knock), becomes very important as cylinder head temps and compression pressure goes up. Thus Eville Rich's comments in regards to forced induction engines. Especially when running a turbo, (exhaust driven supercharger), the natural tendency for cylinder head and exhaust manifold temps to get really hot cause a greater tendency for the air/fuel charge to ignite before the spark plugs fire, (pre-ignition/knock). When this occurs, there is a lean condition since the piston is not yet at TDC or very near it for firing position, (usually slightly before TDC). In a lean condition the engine will burn the next available fuel... often the aluminum of the pistons.

 

[WJBertrand]

Yeah, but you're a Euro-Dog. We can't even buy that stuff in the US.

Actually you can. Fuel in Europe is rated by the RON system, as a rule of thumb, take 4 octane points off to get to pump octane number, which is the value our pumps in the US are labeled with. Therefore 95 octane Euro = 91 octane US.

There is still the misconception that higher octane means higher power. This simply not true in the absence of any tuning adjustment. To get the higher octane numbers, alcohol or in the past (MTBE) was added to fuel to slow the burning rate and avoid knock. Since alcohol and MTBE have less energy / gallon than pure gasoline they actually dilute and reduce the total energy in a gallon of premium vs. regular grade fuel. The trade off is that the slower burning fuel will tolerate more aggressive tuning, so the slight loss in available energy is more than made up for by the increased level tune (timing, compression ratio, etc) in a high performance engine. Engines with knock sensing system just automatically adjust the tune, in most cases timing.

My old Honda ST1100 actually started quicker, ran stronger and got better mileage using regular over premium, even at sea level where I live. Of course if I'd heard any knocking I would have switched to premium to stop that happening but at the cost of a slight loss of performance - all engine tuning remaining constant and no knock sensing system.