Octane is a hydrocarbon having 8 single-bonded carbons. Basically when you get a higher octane you get more combustion and a high resistance like Jaybird said, so it will burn hotter. Thus cleaner. And earlier I believe someone said that a higher octane could cause knocking, although this is possible, I do not believe it is likely (at least in our sportbikes) since the PURPOSE of octane is to PREVENT knocking. Just my two cents.

 

I realizer this and am very familiar with the definition of octane. I just never heard of it burning hotter!

 

I guess my understanding has always been that higher octane fuel was neededfor high compression engines to avoid pre-ignition.Higher octane fuelavoids pre-ignition since it burns ata higher temp. With the 12:1 compression of the F4i,I figured that it would run better on higher octane fuel, unless the timinghas already been advanced to compensate for the lower octane fuel.Anyone care to clear it up for me.

 

octane is the stability of the fuel under pressure. the higher the octane the more stable the fuel. you need a high octane fuel because low octane fuels will pre-maturely ignite under high pressure. i haven’t heard that higher octane fuels burn hotter before my self either. Although this might be explained thought the fact that as you compress air it gets hot because of friction in the molecules. not to say that it might not burn hotter but i don’t think it would be very noticeable. i have read in a few places burning to high of an octane means you wount burn all the fuel though.



i been trying to find something on higher octane burning hotter but haven’t if you have a good article on this i would love to read it because im always interested it learning more about how fuels work.

 

i see that this thread is still growing....just like the 40 other previous threadson this subject.

cool, anyway. reason why i dont use 93... or 91...is; because i ride mostly in the summer. in nyc we have humid/damp days and nights during this season. so, the higher octane will not show me any effects other than engine knocking. higher octane needs much denser air to work properly. if you are lacking the proper mixture than all you are doing is overheating your engine and tranny, plus the bike will not thoroughly burn all the gas and you will have more carbon build up in the valve, head and exhaust.

you can use higher octane because they do burn more thoroughly only if you have the proper air amount. however, if you're in humid environment or you live in the montians then you are wasting money on gas and more importantly you are overheating your ride and clogging up you exhaust air ways.

yes, the fuel will burn hotter. based on the fact that the fuel is less dense(high octane), it will allow more air to be compressed with the fuel to create a very highly potential explosion. the higher the potential. the hotter it will be inside the chamber.

 

so my question is to you though is it tuely the fuel buring hotter though or the fact that more air is being aloud in and a higher compression. is it truely the fuel or the compression making it hotter. and how much hotter are we talking here a degree or 20 degrees.

sorry if this a little Redundant but im really interestend in learning more about this

 

the answer is both. because the high compression ratio on our bikes, the air can be pressed into fuel more and therefore on the higher octane fuels you will have more friction between that mix. that friction will result into extra heat in the chamber but not by much. the mix between the denser air fuel and higher oct will result in higher potention explosion and then bla bla bla ( i wrote that in the previous post)....

so to finalize my answer, that both the mix between the air and fuel cause heat and the higher potential will cause greater heat. temperature difference wise its difficult to gauge. it depends on the climate and speeds, thats why its hard to find benchmarks out there. too much crap to list....

btw guys read these things...this guys said the same thing that i did, that from high octane he notice more carbon build up on the valve and other crap..
http://www.downwardspiral.net/motorcycle/octane/

also read this ... this is more for the oil debate on the other thread, but still can be interesting
http://www.nortonclub.com/docs/OilTemp.pdf

 

I hear the octane rating of diesel fuel is pretty good. But they onlyuse that stuffin farmequipment and harleys, so I guess that wouldn't work???

 

I really have never seen quite so much misunderstanding of fuel chemistry in one place before. Some posters have it right, but the majority don't...not even close.

Going for most recent, diesel fuel does not have a "good" octane rating. In fact, it has an octane rating of about 15. Yes, 15. Diesel instead has a "cetane" rating. Since diesel isn't used in gasoline engines, the cetane rating is irrelevant to us. Diesel will cause bad pinging in a spark ignition engine if mixed with gas. It won't even work if used alone.

"Octane" is in fact a hydrocarbon used as a baseline rating to describe a fuel's resistance to autoignition or knock in a spark ignition engine. Autoignition can be caused by lots of boost, lots of compression, oil contamination like that necessary of a 2-stroke, or all the above plus many other factors. Heptane is the antithesis of iso-octane and has an octane rating of 0.

- High octane fuel will not burn "hotter." Did you know that methanol has a motor octane of about 115, yet little more than half the BTU content of gasoline? Compressed natural gas has an octane rating of about 130, but 1/4 the energy content by weight of gasoline. Pump gas has a negligible difference of energy content between the grades.
- The "octane" rating of fuel often has nothing to do with how much actual octane(the hydrocarbon) is in the fuel, therefore the octane rating is independent of the fuel's specific energy content.


The bottom line is that the F4i's ability to run on 87 R+M/2 octane fuel shows how conservative Honda and/or Keihin was with the ignition advance curve. This is especially significant considering there is no knock sensor. Another aspect of being able to run 87 fuel through a 12:1 engine is the relatively high rpm. There is simply less time for the necessary chemical and thermodynamic reactions to take place in the cylinder. An efficient chamber desing also helps. I suspect that if Honda had taken full advantage of their design, none of us would be able to run anything less than 94-96 fuel.

Hopefully I didn't offend anyone too much. There are volumes that could be written on petroleum chemistry, but it's getting late and I'm getting fuzzy headed.

 

I run 87.

The engine doesn't knock with 87.

So 89, 91, or 93 is a COMPLETE AND UTTER WASTE OF MONEY.

If your engine knocks using 87- then go up to 89.