Paul,
Since you have already invested the time and effort to set the engine up
on the dyno, I would suggest using one of Vance's "horsepower required"
plots that you have posted recently.  Advance the throttle and set the
dyno incrementally to absorb the horsepower indicated for each RPM
setting.  Then set the mixture for whatever criteria you decide (best
BSFC, certain EGT, maximum power, or whatever), advance to a new
horsepower and RPM and repeat the process until you have covered the
complete RPM range.  This would simulate a certain fixed pitch prop and
would give you a pair of data points to set into the dyno.  The result
would be a set of data elements that traced diagonally across the
mixture array.  (I prefer not to call it a map to avoid confusion with
the Manifold Abs. Press)  You could then guess at the numbers for the
remainder of the array to give a safe array to work with.

Aubrey Thompson

Unfortunately we have kind of wasted the past few days by
using a Innovate mixture monitor that was unreliable.
We were severely misled.
We are now paying more attention to BSFC for an indication
of what the mixture should be. We are going to try to get it
near the ball park and do some high RPM runs. Final tuning should
be done in the air with prop load.

Paul Lamar

It would seem to me that it should be much easier, and more meaningful to
map an engine's
characteristics with a dyno than with even a controllable prop. In addition
to the extra physical
hazard of a flailing propeller and hurricane class winds, the propeller
would give you
a smaller range of control. The classic bhp curve is a full throttle curve,
with the load
varied to limit rpm. Then you can vary mixture within safe limits to see how
the power
shifts with lean, power rich, and over rich conditions. I suspect from your
limited
data that you are not very much over "power rich" at your data points. I do
not believe that
you will be able to significantly increase power as you lean. Get data! lots
of points!
and map them out later.
Vance

So far Vance the mixture monitor has scared the heck out of
us by suddenly going full lean without warning. We are worried
about detonation and fractured apex seals. I need more confidence
in the mixture monitoring area before I can make meaningful changes
in the map. If you want to observe come on down to Mazdatrix
in Signal Hill. I am in the process of talking Dave into
installing a conventional O2 sensors in each exhaust pipe and buying
a cheap mixture monitors at Napa Auto parts. That way we will
have several measurements that should correlate.

You might be right about getting much more power at the proper
12.5:1 mixture setting. I suspect the intake runners are too long.
I think the rate of HP increase with RPM is reducing indicating
the tubes are too long. I will know for sure when we do
a few more runs.


Paul Lamar