Octane

[fahrvegnugen at cox.net (David Utley)]

Matt,
  Good link, lots of interesting details there, including this bit just
below where you stopped...

'It might seem odd that fuels with higher octane ratings burn less easily,
yet are popularly thought of as more powerful. Using a fuel with a higher
octane allows an engine to be run at a higher compression ratio without
having problems with knock. Compression is directly related to power, so
engines that require higher octane usually deliver more power. Some
high-performance engines are designed to operate with a compression ratio
associated with high octane numbers, and thus demand high-octane petrol. It
should be noted that the power output of an engine also depends on the
energy content of its fuel, which bears no simple relationship to the octane
rating. Some people believe that adding a higher octane fuel to their engine
will increase its performance or lessen its fuel consumption. This is
false - engines perform best when using fuel with the octane rating they
were designed for.'

I don't know how to answer, except to say that my experience is not backing
up what they have said.  Perhaps because this engine is nearly as much an
oil burner as it is gas, perhaps because my throttle only has two positions,
I dunno.  While the ass-dyno gets a bad name for being inconsistent and
biased (esp. my ass-dyno), I have had other ass-dynos confirm my findings
too, for what it is worth...

I will continue searching for more details, I am more confused now...

David
-----Original Message-----
From: scirocco-l-bounces+fahrvegnugen=cox.net@scirocco.org
[mailto:scirocco-l-bounces+fahrvegnugen=cox.net@scirocco.org]On Behalf Of
matt
Sent: Saturday, July 02, 2005 8:04 PM
To: scirocco-l@scirocco.org
Subject: Octane

ok i pulled this form here
http://encyclopedia.laborlawtalk.com/octane_rating

It supports my argument that that the stock 8v is fine with 87

Octane rating

The most important characteristic of petrol is its Research Octane Number
(RON) or octane rating, which is a measure of how resistant petrol is to
premature detonation (knocking). It is measured relative to a mixture of
isooctane (2,2,4-trimethylpentane) and n-heptane. So an 87-octane petrol has
the same knock resistance as a mixture of 87% isooctane and 13% n-heptane.

There is another type of Octane, called "Motor Octane Number" (MON), which
is a better measure of how the fuel behaves when under load. Its definition
is also based on the mixture of isooctane and n-heptane that has the same
performance. Depending on the composition of the fuel, the MON of a modern
petrol will be about 10 points lower than the RON. Normally fuel
specifications require both a minimum RON and a minimum MON.

In most countries (including all of Europe and Australia) the 'headline'
octane that would be shown on the pump is the RON: but in the United States
and some other countries the headline number is in fact the average of the
RON and the MON, sometimes called the "Road Octane Number" or RON. Because
of the 10 point difference noted above this means that the octane in the
United States will be about 5 points lower than the same fuel elsewhere: 87
octane fuel in the United States would be 92 in Europe.

It is possible for a fuel to have a RON greater than 100. This reflects the
fact that isooctane is not the most knock-resistant substance available.
Racing fuels, Avgas and LPG typically have octane ratings of 110 or
significantly higher.


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