Is it my imagination? (Octane...)

[Checkswrecks]

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 an 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.

He said they have 120 RON which would be 115 Octane in the US. Even the race gas here isn't that high.

 

[magic]

I think there is another variable in the octane game. I pull into a local gas station and each pump has 3 selections, 87 octane regular which is 10% ethanol, 89 octane midgrade which may or may not contain ethanol and 91 octane premium which is 100% gasoline no ethanol added. Each pump has one hose that dispenses all 3 grades. If I select premium and the guy before me bought regular how much regular gas comes out before I get premium? I have never seen the pump or the related underground piping that dispenses gasoline, but I suspect there is at least a couple gallons of regular laying in the lines. So, we might not even know what we're putting in our bikes.

I usually fill my bikes at home with 6 gallon cans. At the gas station, I put about 5 gallons of premium in my truck and then fill a few 6 gallon cans for the bikes. I know this sounds a little crazy, but it's for my bikes. Out on the road if the gas station has separate pumps and hoses, I will buy premium. Otherwise I will just buy regular. I really don't notice any difference in the mileage or performance. Anybody have any knowledge of what goes on with a gas pump that dispenses multiple grades of gas?

 

[Checkswrecks]

I think there is another variable in the octane game. I pull into a local gas station and each pump has 3 selections, 87 octane regular which is 10% ethanol, 89 octane midgrade which may or may not contain ethanol and 91 octane premium which is 100% gasoline no ethanol added. Each pump has one hose that dispenses all 3 grades. If I select premium and the guy before me bought regular how much regular gas comes out before I get premium? I have never seen the pump or the related underground piping that dispenses gasoline, but I suspect there is at least a couple gallons of regular laying in the lines. So, we might not even know what we're putting in our bikes.

I usually fill my bikes at home with 6 gallon cans. At the gas station, I put about 5 gallons of premium in my truck and then fill a few 6 gallon cans for the bikes. I know this sounds a little crazy, but it's for my bikes. Out on the road if the gas station has separate pumps and hoses, I will buy premium. Otherwise I will just buy regular. I really don't notice any difference in the mileage or performance. Anybody have any knowledge of what goes on with a gas pump that dispenses multiple grades of gas?

There've been a LOT of articles about potential dilution in these "blender" pumps (one hose for multiple grades) since the introduction of alcohol. The EPA requires sales from E15 pumps to be a minimum of 4 gallons to dilute the residual of about a quart. It's stupid, if just because a number of bikes (my KTM for example) have a smaller tank than that. Good thing that most pumps are 10%, not 15%.

 

[EricV]

I think there is another variable in the octane game. <snip> Anybody have any knowledge of what goes on with a gas pump that dispenses multiple grades of gas?

Those are called "mixer pumps" They mix premium and low octane to get mid grade, (along with ethanol blending). Most places the premium still has the same percentage of ethanal in it as the other grades, unless it has a separate hose and is specifically labeled as non-ethanol.

Mini lesson in energy storage. Pure gasoline has 114,000 btu/gal. Ethanol has 81,800 btu/gal. The more ethanol you add to gasoline, the less energy it will provide. I.E. The more you will have to burn to go the same distance in your vehicle. E-10 is rated at a claimed 111,836 btu/gal, but that's 98.14% og gasoline and I'm not buying that when my MPG went from 46/48 mpg to a steady 42 mpg when using E-10. Nearly a 10% drop.

Just as an aside, #2 Diesel has 129,500 btu/gal. More than anything else commonly used.

Octane is not a measure or indicator of Hp. Higher Hp engines are usually running higher compression engines and need that slower ignition to avoid pre-detonation, but it's not the higher octane making the power, it's just a requirement to run those higher compression numbers and more boost in forced induction engines.

 

[magic]

There are plenty of gas stations around this part of Wisconsin that advertise 91 octane 100% gasoline with no ethanol. However with these mixer pumps we may not be getting the premium that we are paying for. If you want to top off your bike and it takes only 2 or 3 gallons I have to believe that most of that will be regular with ethanol mixed in. Buying 100% premium gas is kind of a big deal for the serious snowmobile, motorcycle and boat guys.

 

[WJBertrand]

He said they have 120 RON which would be 115 Octane in the US. Even the race gas here isn't that high.

My bad I was responding with the 95 octane recommendation in mind in the owner's manual for the Super T in Europe. I thought that's what was being responded to.

 

[Eville Rich]

Regarding the energy content of gasoline vs ethanol, you have to watch whether they are talking lower heating value or higher heating value. The lower heating value relates to the water vapor that is created through combustion only returning to 150 C from 25 C, whereas the higher heating value captures the full heat of vaporization, returning the water vapor to 25 C. It's not that important, but in general gasoline has a lower heating value of 116,000 BTU/gal (US gallon) and ethanol has a lower heating value of 76,000 BTU. This compares to about 124,000 BTU/gal and 84,000 BTU/gal at the higher heating value. Either way the energy ratio per volume is the same. So E10 will be 112,000 BTU at the lower heating value and 120,000 BTU/gal at the higher heating value. Roughly 96 percent the energy content of just gasoline. I apologize for being pedantic while also using round numbers. ;D

Regardless, the purpose of ethanol is largely for emissions management (ignoring the farm lobby politics for now). Ethanol keeps down the heat of combustion which helps avoid the creation of NOx pollutants, which are pretty nasty. Ethanol also acts as an octane booster. Straight up ethanol has a AKI (RON+MON)/2 of about 99. So adding ethanol is one way for gas companies to inexpensively boost the octane rating of gasoline. I've noticed that around here, the 91 octane gas tends to be ethanol free, while the 93 octane gas tends to be "up to 10 percent." The base gasoline we get is pretty much all the same, with differences based on additives (e.g. Top Tier additives). I assume that those selling 93 octane at 10 percent ethanol are really getting the same base 91 octane gas and getting to 93 with the ethanol. It's pretty close math, allowing for rounding.

Eville Rich
2016 S10
2015 WR250R

 

[tubebender]

Eville Rich has really explained it well.
Here in California, Ethanol replaced MTBE (nasty stuff) as the oxygenate in fuel for the reasons explained above.
If you read the fine print on the pumps, it says "Can contain up to 10% Ethanol". I haven't found any specific written evidence, but I speculate that Premium has more ethanol then regular to increase the octane rating (which, BTW, is mixed in at tanker fill)

Here is a older Chevron paper that explains everything you ever wanted to know about gasoline.

http://www.chevronwithtechron.ca/products/documents/69083_MotorGas_Tech_Review.pdf