Miata Mailing List: August 1993, Message #138
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   From: MANSON@fsd.com
Subject: 14 BTDC Timing Adjustment
   Date: Thu, 19 Aug 1993 10:16:30 -0400


Miata Masters
I have been digesting the 14 degree adjustment discussion with skepticizm.
Although the Miata Mag mentioned it in some past issue (before I joined),
was it provided by an authoritative source, or someone with a good idea and
some engine know-how?

In my experience with engine theory from many years ago, one of the main
concerns with timing advances was excess heat and pressure on the tops of
the pistons.  One fear in the old days was burning through the piston top
because of hot combustion chambers and overly pressured chambers.  This may
no longer be of concern with todays materials and mechanical designs.  (I seem
to racall the mention of burned valves as well but it is not as clear in my
memory.)

The comment regarding the need for premium fuel does certainly make sense
since we are effectively increasing both heat and pressure during the combus-
tion process (the basic value of premium being its inhibition to pre-detonation
under those conditions).

One of the most significant questions is whether the change has had any
significant improvement over the engine operation (horsepower/torque output),
and if there is any documented evidence of the improvement (dyno testing).  I
would be much more receptive to such a change (even thought it only a 4 degree
change) if there were such improvement and evidence.

The next most significant question is - What happens if we go further (i.e.,
15 degrees or 16 degrees) and where the edge of disadvantage or damage starts
to occur?  In setting timing, although we try to be exact, we can make errors
and that setting may drift.  How much of a safety margin is there from the 14
degree setting?

I am sure that many of these are either presently unanswerable, or have been
addressed elsewhere (reference?).  If I am wasting my time asking, let me know.
But as usual, I am generally curious about these things, and not always
willing to experiment on my own hardware if significant risks are involved.

Tom Manson
Manson@fsd.com
Disclaimer: My spelling is immaculate, it's the computer and keyboard that
make all of my mistakes.