<<Advancing one spark may be better than none, but the flame fronts start
at different times - It is best to fire both plugs at the same time.  But,
some people settle for 1/2 a system as it makes them comfortable with the
apparent risk/reward.  No Dyno test is a replacement for a flight test.
Best is two planes side by side in a race.  What's a timing sweep?  Unison
and E-Mag keep their timing secret, Lightspeed has an optional display so
you can monitor the timing (change it if you dare, too).  Scott Krueger AKA
Grayhawk>>

Thanks for all the references, Scott.  Lasar seems to have some reasonable
data in their website and overall, the responses I get show an improvement
in BSFC at altitude of between 6 and 12 percent with between 60 and 90
percent of that available with a single advancing ignition system.
Unfortunately, none of the data is for LOP operation, which I would expect
to result in greater improvements.  I disagree that a dyno test is no
substitute for flight testing - in a dyno test all other variables can be
eliminated so accurate comparisons can be made.  Even Unison uses static rpm
as a measure of power - not very accurate compared to a balance beam on a
dyno engine.  A "timing sweep" typically results in a graph that shows a
single variable (BSFC or power) changing as a result of ignition advance.
The fuel mixture can be held at a fixed value or can be set at LBT as the
ignition timing is changed.  The knowledge can be derived from an accurate
and thorough dyno test may not be available from a flight test although the
flight test is the end result.

Gary Casey