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Re: Octane Requirements


On 27 Nov 97, Allen Moore wrote:

> Everett + Jennepher wrote:
> >
> > The Volkswagen 1500 with the twin-carburetor engine must be run on 
> < premium
> > fuel with an octane rating of at least 95.*)"
> > 
> > I assume this applies to all 1961-1967 carbureted T3s.
 
>    When was the last time ANYBODY saw fuel of that octane rating? (!) 

>    Hoping 93 would work as well...

There are two different scales for measuring octane: RON (Research 
Octane Number) and MON (Motor Octane Number).  Each method has its 
proponents and good reasons to exist, but they are not the same.  The 
gas at US pumps is measured by the average of the two: (RON +MON)/2.

VW, however, when these cars were built, was using the larger of the 
two numbers.  This works out to mean that the 95 that VW asks for is 
about the same as the 93 you can buy.  No problem.

At the time I don't think this was considered "high-test", as 98 and 
101 or 103 were available.  As octane has come down in an attempt to 
keep gas prices stable the best solution is to reduce your 
compression ratio any time you do a rebuild to accomodate what's now 
commonly available.  This seems to work with no loss of performance.

Jim
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       Melissa Kepner                                    Jim Adney
                             Laura Kepner-Adney
                         jadney@vwtype3.org      
                             Madison, Wisconsin
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