Re: octane and engine health

[bearbvd@domain.elided (Greg Hermann)]

At 12:16 AM 6/6/02, Jorge & Ani Mazlumian wrote:
>It's been discussed many times here.  I don't know if this question has been
>answered, though:
>I understand that higher octane than recommended in a street engine will not
>add horsepower.  But will it protect the engine from knocking under more
>extreme driving, such as time trials?
>Here in California we have to get 91 octane gas now.  And it's probably ok
>for the street.  However, if after getting relatively hot at the track, the
>engine would start knocking, I would propose that a mix with higher octane
>gas may prevent that.
>Would like to see a discussion, or at least a reference to where I can read
>about it.
>
>Jorge Mazlumian
>89 Verde with toast engine at the track (91 octane)
>--
Octane is a very weird subject any more.

First, consider the "hockey puck" shape of the combustion chamber on the
(ANCIENT) Waukesha test engine which is used to develop standardized octane
ratings. The way a fuel behaves in the test chamber is nearly irrelevant to
what goes on in a modern high squish/swirl chamber !!

One thing that is for sure: lower octane fuel burns FASTER than higher
octane fuel. In many cases, this means that running premium will bring
about a REDUCTION in power and economy -not just no change. And, this is
particularly true in Kalifornia, where the higher octane rating often
simply means they dumped more MTBE into the witch's brew !

I have heard of many cases in which an engine with modern chambers would
run just FINE on ULR, but begin to ping and mis-behave on (what, today,
passes for) premium !!! This phenomenon is pretty much a function of the
slower burn rate of the "premium" fuel-detonation is, after all, in part a
function of time.

Greg
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