[CeeBeeArr]

I have always been curious as to why there is a theory that higher octane gas than is necessary for a particular engine is considered a good thing. My understanding is that the required octane number depends upon the compression ratio.

To make it even more confusing to me, when I was young, 10.6 to 1 compression ratio was high compression and required premium; 7 to 1 was the compression ratio for regular.

Is it the fuel injection? Control over ignition timing? Is there a knock sensor in the engine to even know that detonation is occurring?

I know a certain amount about the subject but am always glad to learn more.

 

[somebody5788]

Octane does not provide more energy. There are 2 things that make a vehicle require higher octane fuel. Ignition timing and compression ratio. If you run to much ignition timing with somewhat higher compression then you will get detonation. So for 10.7:1 compression ratio they run a lot less ignition timing in order to be able to use low octane.

Where octane does come into play with giving more power is when you start using really advanced ignition timing. This means the fuel is detonated at the most optimal part of the stroke to provide the most leverage on the crank shaft possible therefore more power. A higher compression ratio provides more power with less fuel because it's confining the same explosion to a smaller compressed space.

 

[CeeBeeArr]

Octane does not provide more energy. There are 2 things that make a vehicle require higher octane fuel. Ignition timing and compression ratio. If you run to much ignition timing with somewhat higher compression then you will get detonation. So for 10.7:1 compression ratio they run a lot less ignition timing in order to be able to use low octane.

Can the CBR250 engine ECM take advantage of higher octane fuel by advancing the ignition timing appropriately for the rpm?

 

[somebody5788]

Can the CBR250 engine ECM take advantage of higher octane fuel by advancing the ignition timing appropriately for the rpm?

I don't think from factory it has enough range. When some of the "tunes" come out for them you'll be able to plug in and reflash them for higher octane.

I run 93 octane from Shell just because they put additives in it to keep your engine clean. And I know they actually work lol

 

[Luke]

Fuel Injection and ECMs let manufactuers get closer to the "edge". Detonation is bad - but it's not something that constant. Engine temp, load, air density, etc. play into whether detonation occurs. In the past, those factors could not be analysed in real time, so Premium was specified as insurance. Now the ECM analyses all of those factors and optimizes the fuel / air ratio and timing. In addition, combustion chambers do a much better job of mixing the fuel and air to avoid lean conditions. Last but not least, the ECM can detect detonation and make it stop by adjusting one or more of the things it controls.

The CBR has 10.7-1 compression, but I've seen higher ratios with regular (e.g. 11.2 on the new CB1000R). I'm not convinced that premium does anything good for the 250 (aside from the extra additives somebody5788 mentioned). In fact, most "experts" will tell you that premium can make your engine run worse. to wit:

"Premium, in fact, sometimes is worse fuel than regular. It resists knock because it's harder to ignite than lower-octane fuels. As a result, some engines won't start as quickly or run as smoothly on premium"
(source: USATODAY.com - Why use premium gas when regular will do? )

"Some automotive types claim that using premium in a car designed for regular will make the engine dirtier--something about deposits on the back side of the intake valves. I've also heard that slower-burning high-octane gas produces less power when used in ordinary cars. Believe what you like; the point is, don't assume "premium" means "better."
(source: The Straight Dope: What's the difference between premium and regular gas? )

Just like (most) everything else, it's a choice - everybody makes their own. My personal take is that if the manual says premium, I'll run premium (even though those same articles say that the ECMs in Premium-fuel engines will work just fine if you use regular). My CBR250 manual says regular.

 

[CeeBeeArr]

I did a bit of checking on the CBR250 electrical diagram and I don't see a knock sensor. So I think the following conclusions are valid:
1 - If the fuel has a minimum AKI octane of 86 then it can be expected to work fine.
2 - Higher octane fuels are higher quality and contain additives that help keep an engine in good condition. That in itself is a reason to use them. But don't expect more power from them on a stock CBR250.
3 - There is no difference in power between fuels of differing octane if the gasoline/ethanol ratio is the same. Pure gasoline fuels of minimum 86 octane can be expected to deliver the highest fuel efficiency.
4 - Ethanol increases the octane number but delivers less energy per unit volume. So less km/liter. We live in hope that the ECM calculates and delivers the optimal mixture of fuel and air for the available fuel.
5 - Since there is no way for a CBR250 ECM to know the octane of fuel, it is probably configured for the lowest octane in terms of ignition timing and possibly other things.
6 - The good news is that it is probably possible to get more performance out of an already excellent engine by using some ECM programming and premium fuel since it is likely that it (the engine) is not running optimally when using 86 octane.

I am very curious as to what can be done with this engine. Yesterday, I came back into town from a 300km road trip with a slight tailwind and did a pass that ended at 143km/hour. Absolutely amazing, fun, exciting, scary and I loved it. I see now why people drive these things. Something about the joy of life in it somewhere...

 

[spdklls]

I did a bit of checking on the CBR250 electrical diagram and I don't see a knock sensor. So I think the following conclusions are valid:
1 - If the fuel has a minimum AKI octane of 86 then it can be expected to work fine.
2 - Higher octane fuels are higher quality and contain additives that help keep an engine in good condition. That in itself is a reason to use them. But don't expect more power from them on a stock CBR250.
3 - There is no difference in power between fuels of differing octane if the gasoline/ethanol ratio is the same. Pure gasoline fuels of minimum 86 octane can be expected to deliver the highest fuel efficiency.
4 - Ethanol increases the octane number but delivers less energy per unit volume. So less km/liter. We live in hope that the ECM calculates and delivers the optimal mixture of fuel and air for the available fuel.
5 - Since there is no way for a CBR250 ECM to know the octane of fuel, it is probably configured for the lowest octane in terms of ignition timing and possibly other things.
6 - The good news is that it is probably possible to get more performance out of an already excellent engine by using some ECM programming and premium fuel since it is likely that it (the engine) is not running optimally when using 86 octane.

I am very curious as to what can be done with this engine. Yesterday, I came back into town from a 300km road trip with a slight tailwind and did a pass that ended at 143km/hour. Absolutely amazing, fun, exciting, scary and I loved it. I see now why people drive these things. Something about the joy of life in it somewhere...

Sorry..i did some checking too and higher octane fuels in fact..DO NOT contain anything different from lower octane fuels than more hydrocarbons that are refined more to burn slower...end of difference...all octanes contain the exact same additives,....feel free to research it and prove me wrong

 

[CeeBeeArr]

Sorry..i did some checking too and higher octane fuels in fact..DO NOT contain anything different from lower octane fuels than more hydrocarbons that are refined more to burn slower...end of difference...all octanes contain the exact same additives,....feel free to research it and prove me wrong

I was a bit afraid to write what I did but didn't want to sound too vague. Thanks for the correction.

 

[somebody5788]

Sorry..i did some checking too and higher octane fuels in fact..DO NOT contain anything different from lower octane fuels than more hydrocarbons that are refined more to burn slower...end of difference...all octanes contain the exact same additives,....feel free to research it and prove me wrong

In the United States (U.S.), at around 2004, all U.S. Shell gas "Premium" was rebranded as "V-Power". In 2008, Shell in the U.S. launched the new Nitrogen-Enriched Shell V-Power.

Yes it's specifically Shell that I was referring to and I forgot to add that but it is the only one that shell does this to. They do not do it to their lower grade fuels. And it does in fact keep the engine cleaner. There have been several tests that have shown this.

Read the nitrogen portion and continue on the next page. It's not all just claims they actually exceed the optional standards for fuel that several automotive manufacturers requested including Honda http://auto.howstuffworks.com/fuel-efficiency/alternative-fuels/nitrogen-enriched-gasoline1.htm