Date:         Mon, 19 Sep 1994 07:52:39 -0400
Sender:       Vanagon Mailing List <vanagon@vanagon.com>
From:         hseaver@nyx.cs.du.edu (Harmon Seaver)
Subject:      Re: super vs. regular?

> > > Food for thought (fuel for VW's):  does anyone have an opinion
> > > (silly question!) as to whether super or regular gasoline makes
> > > a VW run hotter?
> > > 
> > 
> 	I don't know about hotter, but I know better.
> 
> 	92 Octane-Yes. The kids in Wolfsburg spec. 91 Octane in the manual for
> 	my '91.
> 
> 	I use Chevron Super. Ruby runs better and cleaner.
> 	
> > run the super in your rig.
> > 
> 	10-4
> 
> > the higher octane will allow your engine to run more eficiantly, and 
> > therefore cooler.

    Not necessarily -- you guys are speaking totally subjectively, and
ignoring the facts. The technical, scientific fact is that the lower the
octane of gasoline, the more power it produces. High octance ratings are
obtained by adding various substances which reduce the actual "explosive"
quality of gasoline. Reason is, higher compression engines will create 
enough compression pressure to detonate the fuel mix before the spark 
even goes off -- obviously undesirable. Can even damage the engine. So -
if your engine is of high enough compression to require a certain octane
rating, then you have to use that or get poorer performance, even wreck
the engine. However, if your engine is lower compression -- like 7.5:1 --
then high octane gas is not only a waste of money, but actually gives 
you less power, and thus, less miles per gallon.
   As far as running cooler -- yes, higher octane might run cooler --
because it has less power actually, ounce for ounce.

> 	Maybe, but even if it did cost more, as long as I'm not in hand-to-
> 	mouth mode, I prefer to burn the best fuel.

     There is no "best" in regards to regular or premium -- only what is
"best" for your particular engine. "Best" in regards to the cleanliness
of the fuel, etc. -- yes. For instance, if you have an engine with fuel
injection, you quickly (if you are mechanically aware, that is) learn
which gas station in your area has decent fuel which won't clog your 
injectors. Having said that, I should also say that very often the same
fuel distributor delivers the exact same gasoline to a number of different
"Name Brand" gas stations. So whether you are getting Shell or Amoco is
often irrelevent. This is particularly true of tourist areas.

    Another thing which makes considerable difference, on which fuel you
can use, besides your compression ratio, is your ignition timing. You
might have a lower C/R, but because of the timing advance, get detonation
with low octane. On the older engines, you are better off with putting
in a straight centrifugal advance, like the Bosch 009 distributor. On the
newer ones, you best leave alone. Unless you can get a "high performance"
replacement for the onboard computer. Don't know if those are available
for VWs, like they are for the detroit iron.

Harmon Seaver 
hseaver@nyx.cs.du.edu

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