Re: Bonzo caught lying again

On Sat, 02 Aug 2008 16:40:07 -0700, BottleBob <bottlbob@xxxxxxxxxxxxx> wrote:



Cliff wrote:

<snip>

Higher octane does not get better MPG either AFAIK.

The correct response to that would be, "it depends". This being a
timely subject these days, I'll make a few comments.
Lower combustion pressure engines (normally aspirated low compression
ratio engines) that do not experience detonation with low octane
gasoline will not benefit from using a higher octane fuel. This is NOT
one of those cases where you will automatically get what you pay for.
The octane rating of a gasoline relates to its ability to resist
detonation (knock), it does not relate to its energy content OR its
flame front speed. In other words, the common misconception that
higher octane gasolines reduce detonation because they are "slower
burning" is a myth.

Is it?
The Octane has a higher molecular weight IIRC. This may then
take longer to fully combust.

BUT, and this is a BIG but; *IF* you are running a high combustion
pressure engine (either a high static compression ratio OR low
compression ratio with significant boost from a turbo or supercharger),

Such as a diesel?

which IS prone to detonation, then using a lower octane fuel that
causes the engine management system to retard the spark and/or richen
the mixture... you'll be running the engine inefficiently and no-doubt
hurting your power AND mileage. You may never hear any
pinging/knocking due to the speed of the electronic knock-sensing and
retardation system, so might be led to believe that lower octane fuel
is more than adequate, when it may not be.

Nobody said that lower octane was better for high compression.

Speaking of which ... think of having to use gasoline to get a
diesel engine to even run a little bit when somebody is "cooling"
it with "water injection" <VBG>.
--
Cliff
.

Relevant Pages

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