<VV>Octane/Ping

[Eric S. Eberhard]

You are correct!  The reason people associate higher power with higher 
octane is that higher octane does allow higher compression, different 
ignition timing, and so forth -- and these things can increase 
power!  Premium in a car that does not need it is at best a waste, and can 
even decrease mileage a little.

At 05:13 PM 6/22/2005, Padgett wrote:

>>  Re: Octane/Ping
><rant>
>OY! Read my lips: if there is any difference in BTUs between regular and 
>premium, it is premium that has less.
>
>Engines run best and give maximum mpg on the *minimum* octane gasoline 
>that allows complete combustion without detonation (ping).
>
>Keep in mind that we are really talking a fairly narrow range of engine 
>characteristics and an equally narrow range of octane numbers and for my 
>purposes, at or close to sea level.
>
>"Premium" gasolines have additives to slow down the flame propagation rate 
>and raise the flash point. They do not add to the "power" of the gasoline 
>but rather change its burn (you want an even burn of the mixture and for 
>economy cruise you want it a lot leaner than stochiometric) properties.
>
>Even burn in a SI engine is a steady and complete combustion of the 
>mixture from a single flame front starting at the spark plug. If a second 
>flame front starts from a hot spot or the exhaust valve (why you index 
>plugs tby pointing the gap at the exhaust valve) nasty things happen when 
>they collide (the knock or ping) but mainly because the mixture burns much 
>faster (two flame fronts ~ twice as fast) than planned and max pressure 
>occurs too early. (see previous posts).
>
>Once you wrap your mind around the fact that inside the combustion chamber 
>you want an even burn that takes a measureable amount of time and 
>concludes at a particular point, everything gets much easier.
>
>This is why my original observation was that a N/A engine with only 9:1 
>compression and a 3 1/2" bore should not require over 89 PON (and probably 
>87) to develop maximum power, Something I intend to prove once I find the 
>right car.
></rant>
>
>Padgett
>
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Eric S. Eberhard
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