Date:         Mon, 24 Jun 1996 09:47:45 -0700 (PDT)
Sender:       Vanagon Mailing List <vanagon@vanagon.com>
From:         eugp@uclink3.berkeley.edu (Eugene C. Palmer)
Subject:      Octane ratings


>> 91 octane?!  I beg to differ!  VW engines were built to handle cheap 
>>low quality gas all around the world, like in places where they say 
>>"octane?  what the hel
>> 
>
>When the VW was designed, 93 octane fuel WAS cheap gas.
>
>The cover to my '68 TII fuel fill says "91 Octane minium".
>
>I feel that if the VW people tell me 91 is what I need, thats good enough 
>for me.
>
>If you run cheap fuel, drop your timing back 2 or 3 degrees to keep from 
>overheating.
>

I guess this is one of those discussions that could have the subject heading
changed to reflect the new suject matter.

I understand octane and timing to be closely related to compression.  More
compression, less timing.  So the 1968 T2 was 7.7:1 and required 91 octane
to run cool at 7.5 deg. BTDC.  The extreme conditions manual states that if
a bus is going where there is questionable fuel, that dished pistons are to
be fitted.  VW lowered to CR several times since then, down to 7.0:1 in
1971, and I think they're down to 6.6:1 these days and aren't whining about
91 octane.  I run 12 deg BTDC on 87 octane with engine compression lowered
to 6.7 or 6.8:1.  

So, y'all should be careful when you ask for a rebuilt or new engine.  Make
sure the builder gets the compression set-up the way you want it.


Eug,
'71

PS check out <http://ram.chem.tulane.edu:8080/f-body/trivia/gasoline.html>
for all your fuel questions.