-----------snip--------------

I'm considering repowering my murphy rebel upgrading from an 0-290 to
a 0-320 clone. one of the options I'm considering is an electronic
ignition instead of new slicks. The cost isn't much but I'm not sure
if it would make much difference with my low and slow plane. The prop
will be fixed pitch probably a prince composite prop to keep the
weight down.

Based again on theory only; I would expect little or no change in sea level
power, but a useful improvement in cruise economy with your fixed pitch prop
application. However, the same theory also suggests more torque, with
resultant increase in RPM, when you operate with the same prop from a
hot-and-high airfield--or in the later stages of any climb to cruising
altitude.

Personally, I really like the e-mag concept--presuming that you use 2 of
them and connect the MAP sensing feature. I would be inclined to check with
E-mag Ignitions, the "clone builder" and also with Murphy. At the very
least, there is a possibility that the recommended prop pitch may
change--any prop is a compromise, and a fixed or ground adjustable prop is
more so.

BTW, while I can't give any theoretical support to an improvement in maximum
power, and I steadfastly maintain that there should not be, I admit that it
is quite possible. Electronic ignitions certainly do well on cars: they
are easy starting, give excellent spark plug life, and have shown
outstanding reliability for at least the last 20 years.

Peter