Re: 100 octane Sunoco, was Fuel Octane for 86 4KS

[C1J1Miller@aol.com]

In a message dated 10/29/98 09:13:32 AM Eastern Standard Time,
brandon@cardinalventures.com writes:

> Question:  can a 3B benefit from higher octanes, or is there a limit to how
>  far it will advance parameters in the absence of knock?  I know there is a
>  "learning curve" that limits any benefit from occurring all at once.
>  

I believe the earlier audi cars included two timing maps; one for premium, and
one for regular.  The specs for the 3B read similar; can run regular, premium
recommended for max performance.  I believe recommended octane in USA numbers
is 91.(?)

Ned Ritchie of Intended Acceleration suggested a trick:  after filling with
race gas, pull the fuses to the computer.  This will reset the adapted values,
and when you start up, it will assume the best timing map.  Immediately start
driving aggressively, and that's what it'll adapt to.  I'd recommend doing
this with a warm engine.

I'd say racing gas on the stock computer will only aid you if you're running
the car extremely hard, and getting spark retard due to impending knock (such
as a track day).  With the modified computers, ask the person who did the
mods... some are set up for premium only...

For the earlier 4kq 5-cylinder with no knock sensor, the premium will only
help if you're running advanced timing, or have somehow increased your
compression ratio, etc.  Actually, higher octane fuel resists detonation, and
can make less power, as I understand it; this resistance to detonation lets
the engine timing be advanced further in the stroke.

So, anyone have any real data on optimum octane for a stock 3B?  
chris miller, windham  NH, c1j1miller@aol.com
'91 200q ==>http://members.aol.com/c1j1miller/index.html