<<Properly timed,   an IO-540 operating at WOT at high power (25 to 28"MP)
can have a BFSC down around 0.39 to 395.  (with 8.7:1 pistons).  At lower MP
(20")  the BSFC will not be as good.  A 520/550 class TCM engine will do
about 0385 under the same scenario.
These are very good numbers that the automotive world does not  achieve.
Regards,  George>>

Thanks, George.  However, my question I had in mind was a little more
specific than the one I asked... For someone (me) considering building my
N.A. engine (parallel-valve IO-540) with either two mags or one electronic
ignition and one mag the real question regards the advantage of the one
electronic ignition.  How much advantage at high altitude (20 inches MAP and
lower) is there to advancing one of ignitions and not the other?  How much
advance is appropriate?  What is the optimum advance compared to if both
could advance?  There are some that claim a 20% (maybe they said "up to
20%") BSFC improvement at higher altitudes.

Gary Casey