Waste Spark Ignition, etc

[Neville Newman]

> From: John.Beggs at bchydro.bc.ca (John W. Beggs)
> 
> > Why is everyone so excited over waste-spark ignitions ("dual ended coils")?
> 
> Waste spark (spark on the exhaust stroke which requires very little voltage 
> to fire the plug) is a cost-effective alternative to an independent setup 
> and it provides far better performance than the conventional mechanically 
> driven distributor ignition.
> 
> On an independent ignition system, the ECM determines the correct ignition 
> timing based on cam and crank sensor inputs.  It is possible to fine tune 
> each cylinder to maximize power or emissions or economy.  Just imagine what 
> a NASCAR Winston Cup stock car could achieve with this system.  
> 

In order to implement a waste-spark design, you have to do almost all
of the work you would have to do to implement an independent design, and
it may well cost *more*, not less, to build and maintain.  You have to
select and fire the coils in essentially the same way, the only difference
is whether you select between half as many [logical] coils (you still
have to identify when to fire cyl #1 (or #1 and its mate)).  You can
use a modified distributor body in either case (generally less accurate
because of accumulated gear lash), or you can select off of a crank
(waste-spark) or cam (independent-coil) position sensor.

Most of the coil packs for waste-spark systems that i've seen (of course,
i haven't seen anywhere near all of them) have been potted in pairs,
and in the case of some GM systems at least, have the control module
potted in as well.  This makes it much more expensive when a small
problem occurs.  With an independent set-up, there is no reason that
you couldn't run 4 (or 6 or 8) copies of your favorite conventional
coil at a fraction of the price of the factory twin pack designs.


							-neville