[ffindling]

Chris - I don't think waste spark systems
have any implications as far as emissions
go. Its main advantage is simplicity. By
sharing a single coil between two cylinders, you halve the number of coils
needed. Since the waste spark cylinder
is not under compression at the time of
firing, plug wear is of no significance.
Most of the energy ends up going to the
cylinder that is under compression because the plug in that cylinder is offering a lower resistance path to ground. So in effect, waste spark systems
use cylinder compression to manage
spark distribution. The auto industry has
been using waste spark systems since
the mid 80's and they are well proven.
Although some newer engine designs
such as GM's GEN III and Ford Mod motors (99 up) use coil-on-plug ignition systems where each plug has a separate coil, the main reason for this
was not out any preceived disadvantage of waste spark systems but for OBD II compliance reasons. OBD II mandates that the ECM or powertrain control module report misfire problems and return an error code for each specific cylinder.
By having a separate coil for each plug,
the ECM can determine which cylinder
has a misfire because the separate
coils give each cylinder its own unique
feedback source.

....Fred