<VV>Octane/Ping

[Joe West]

Very well said.. a common misconception is that "premium" is more
volatile... when in fact, the exact opposite is true... higher octane fuel
is more difficult to ignite than it's lower octane counterpart.


On 6/22/05 5:13 PM, "Padgett" <pp2 at 6007.us> 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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Joe West
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