Spitfliers,
I have received a number of questions/comments (off-line) and have
seen some also posted to the list relating to electronic ignitions
vs. points. I'm not "anti-electronic-ignition". I have several,
but I'm also quite fond of the Mallory Dual-Point.
Bob Bollinger had originally asked about what type of system he
might have in his car, and what performance gains he might obtain
by changing to something else. With that in mind, my message
described (and was limited to) the various ignition systems that
were/are commercially available for the Spitfire.
A disadvantage of breaker points is that they produce constant
percentage dwell independent of engine RPM. This is not the optimum
dwell; it is excessive at low RPM and wastes current which does
not further charge the coil. It only makes it hotter. This is
not (directly) a performance drawback though. At high engine speeds,
optimum dwell is not possible with a conventional distributor
ignition system (electronic or points). Ignition coil charge time
is the limiting factor. There simply isn't enought time for it to
fully charge between spark events. Internally ballasted coils go
some way to reducing this limitation. Modern distributor-less
systems overcome it with multiple coils controlled by computers.
If anyone knows of such a system available for our cars I'd be most
interested in hearing about it.
Capacitive discharge systems work well but have inherent limitations
which make them (generally) impractical for road car use. They
dominate the small-engine market (one-cylinder, two- and four-cycle
engines, and marine engines) though.
Fitting a conventional electronic ignition system to your worn (points)
distributor will clear up ignition scatter (due to wear of the dist.
cam and shaft eccentricity) but so will fitting a good distributor.
Eventually you'll need to anyway.
The primary reason electronic ignition systems were introduced on
US Spec. Spitfires is that they enabled the cars to meet EPA
requirements.
--
LBC'ing U,
Bob (& Spitfires)
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http://home.att.net/~stan.part
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