At 09:27 AM 10/3/2002, Malcolm Stebbins wrote:
>I then did a google.com search related to this topic as I was trying to
>find backing for what my mechanic tells me:  Premium gas is 'better' in
>that one can go farther on a tank of premium than on a tank of regular
>and that one should be looking at costs per kilometre/mile rather than
>cost/litre (gallon).

 From Chevron, oxygenated gasoline has about 3.5% less energy content than
non-oxygenated.  About 1/2% of this is due to replacement of higher-energy
high-octane petroleum fractions with very high-octane
ethanol.
http://www.chevron.com/prodserv/fuels/bulletin/oxy-fuel/enrgycon.shtml  So
it seems that there might be as much as a 1% difference in favor of
high-octane non-oxygenated fuel.  Is the price difference 1%?

>   He also suggests that since premium burns more
>slowly (I'll assume that this is correct) that there is more of 'push' on
>the piston and less of a 'slap' therefore being easier on the engine.

It resists detonation and pre-ignition -- that's the point.  But if the
engine isn't doing that, there's no advantage there.

Note that fancier engines with a knock detector may perform better with
high-octane gas but still run correctly with low-octane.  That's not the
case for us, either it works correctly or it doesn't.

david

--
David Beierl - Providence, RI
  http://pws.prserv.net/synergy/Vanagon/
'84 Westy "Dutiful Passage"
'85 GL "Poor Relation"