Ignition Only

[Shannen Durphey]

Axel Rietschin wrote:
> 
> ----- Original Message -----
> From: "Jurgen Hartwig" <jhartwig at midsouth.rr.com>
> 
> > Aside from simplicity and reliability, is there a measureable
> > advantage to running DIS vs. just dizzy, assuming, of course, both are
> > ECM controlled?
> 
> A wasted spark DIS doubles the rpm limit of the ignition system since you
> have twice the number of coils. 
This is not correct.  The max RPM for a distributor based system is
higher provided sufficient firing voltage can be maintained.  The
waste spark of the DIS system will cause problems in engines with
exhaust/intake valve opening overlap as rpm increases.  The waste
spark can fire the incoming intake charge at high rpm.  There are
posts discussing this in the DIY_EFI archives.

Distributor systems with 2 coils, which can alternate between coils
for firing events can significantly increase available spark voltage
at high rpm.
Shannen


A coil-per-cylinder setup pushes the limit
> even higher as a given coil has to fire only once every two revs, compared
> to 4 times per rev as on a V8 engine. This helps maintain powerful sparks
> and decent plug gaps on high-speed, high compression engines, specially
> blown ones. It's probably somewhat cheaper too, and it gives you total
> freedom on the spark timing, which can be important in some special cases,
> such as anti-turbo-lag systems in competition engines.
> 
> --Axel
> 
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