Date:         Wed, 26 Apr 95 16:07:43 PDT
Sender:       Vanagon Mailing List <vanagon@vanagon.com>
From:         Christopher Bose <cbose@math.uvic.ca>
Subject:      Re: Octane ratings

> >	I figure gasoline is like most things- if there's a modest difference
> >in price, the manufacturer is very often selling a markedly better product
> >for the small increment. This sure holds true for food (Compare cheap
> >peanut butter to good stuff, or cheap vegetables to good organics...).
> >The bottom of any market is price driven, and the top is features and
> >customer relations driven. VWs were never the cheapest cars to buy
> >or to own, although they were arguably the best buy for many years.
> 
Well, you might be partly right and partly wrong in your reasoning.
In my opinion you are right that the marketing of gasoline is 
not necessarily designed to give you the best product for the 
least cost. However, it may not be true that premium gas is 
the best buy at all.  As I understand it, (those more knowlegable
please correct me if I am wrong) the higher octane mixes have 
less usable energy than the lower octane fuels, and therefore
represent LESS for MORE money. Another way to put it is, filling 
your baby up with a tank of the "good stuff" may see your mpg 
go DOWN rather than UP as expected.  At the extreme, diesel fuel
(very low octane) contains much more usable energy per unit volume
than any gasoline. Hence the inherent high mpg figures with 
those engines.  So the idea is to use the lowest octane 
fuel which does not cause trouble (pre-ignition mainly) in 
a given engine.  And, as another correspondent already pointed
out, this magic number may vary with engine condition, degree of 
carbon fouling, type of plugs etc. As far as I know, premium 
(ie high octane) fuels are seldom required except in antique
detroit '70's iron and really old carboned up or modified 
engines.

Anyone else care to comment on this?

chris
not as