But if that is true, why do airplanes use higher octane? why do most motors make more HP on a dyno with higher octane? Why are most racing fuels higher (in some cases much) octane? Isn't it more than just preventing preignition? Jestal?fwiw i use either 87 or 89 myself, in both the car and the bike.
No no no no NO!!!!!
The simple answer: High perforance engines NEED higher octane because they were designed that way. For the most part it is the higher compression ratios in those engines (for more HP) that lead to detonation if using low octane fuel. That is why they require high octane - to resist the detonation that can occurr based on the inherent design characteristics of the engine. And its those same design characteristics that happen to require higher octane to resist detonation, that also allow the engine to produce more HP comparatively.
BTW, FJR manual says to us 87 octane unless you experience detonation (pinging).
When the question is why, isn't "No no no no NO!!!!!" the answer to a 4 year old?
I suppose I could have gone on at length to appear more knowledgable than I really am, but the questions still stand. I really want to know more about this. Also, I think I wanted to separate the issues of detonation or ping and generating power.
I am aware that higher compression can cause preigntion or ping or whatever, as well as I am aware that simply retarding the timing will stop/prevent it, but - at the cost of performance/hp. I am aware that additives can and do change the octane of a given distillation of gasoline, or something like that. But, I am not sure that they effect the actual, er, combustion energy is the term used earlier, anyway, I am unsure that is effected much one way or the other. Else we could just use more and put them in diesel fuel.
The "inherent design charateristics" that have an effect on combustion are primarly compression, spark timing, the shape of the chamber at tdc along with temperature, and of course the air fuel mixture. I think we are really only concerned here with the fuel part of that. I see that more dyno hp can result from any method of raising octane and reducing detonation due to the twin effects of being able to raise compression and advance timing.
I strongly suspect that gasoline can be refined to provide more energy from a given unit, thus more hp. I don't know if this would have an effect on ping. I just wondered about that. I stongly suspect that economic and goverment control elements result in a particular grade or whatever of gasoling being refined and then additives are used to adjust the octane to the desired performance or equilivant. Used to be lead, now I don't know what they use. Can the gasoline be refined further to get similar results? or more power from a given unit? If so, why not do so? Would it increase the cost too much? Create more polution?
FWIW, the compression of the FJRs engine is fairly high IIRC, and I felt that 145 crank HP from a normally aspirated <1300 cc engine was pretty high performance as these things go.
That said, I am sorry if my questions aggrevated you Skoot, but I really wanted to know something more than what was here and felt that if I asked, there were those here who could provide those answers. I think I am capable of understanding a more, um, in depth answer but I may very well be deluded and actually just require a stern NO. If you feel so, I will sit down and shut tf up. Just fishing for more information.
So, I apologize for my earlier post. Accepted?
Or is my warning meter about to get some exercise?
Oh, and as I stated earlier, I use 87 or 89 octane. I use the higher octane some because I sometimes experience a little knock or ping at low rpms and I don't like the clatter. Tried 92 as well, but I couldn't tell any real difference other than the price. <_<
