Ignition Only

[Axel Rietschin]

----- Original Message -----
From: "Bruce Plecan" <nacelp at bright.net>
To: <diy_efi at diy-efi.org>
Sent: Thursday, November 09, 2000 6:58 AM
Subject: Re: Ignition Only


> > > 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 absolutely true for a 2 cylinder engine.
> Also, would be firing at the same rate as a single coil, dissy.

Actually, this is true for a 4cyl engine (which I was assuming all along,
BTW), two coils vs one coil. Sorry, I should have said "one coil each two
cylinder". On a 2cyl it will at least save you some weight :)

> >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.
>
> Assuming a 4 stroke,

..well, or once every rev instead of 8 times per rev on a 2-stroke V8
engine, assuming such an engine exists. Anyway, WS-DIS still fires half the
time :)

> > This helps maintain powerful sparks
> > and decent plug gaps on high-speed, high compression engines, specially
> > blown ones.
>
> I may stand corrected on this but
> I'd almost venture a guess MSD, and Crane could prove otherwise.
> Since I don't know of any coil per plug CDs, where as there are CD DISs,
or
> in Crane's CD, you could use 3 on a 3 coil DIS waste spark, for CD DIS.
> 3 CDs on a 3 sets sets of DIS coils vs 6  Coil per Cylinder devises, at
this
> stage of the game I'd say the DIS would win handily.

The race ECUs I'm familiar with (mostly MoTeC and Pectel) have such
coil-per-plug capability. Also, I believe that a coil-per-plug setup would
be _required_ only on the most radical, very high revving engines. F1 folks
spinning V10 engines at 18'000 rpms have no choice :)

> Course we could get insane and go with a CD per coil per cylinder.  $1,400

> just in hardware.

My double dual coil ("4cyl coil pack") costs ~US100 or so. With DIS you
don't need those super-expensive hi-perf coils since they are half
sollicited on wasted spark setups and [do the math, 4, 8] times less with
coil-per-plug on n-cylinder engines.

> >It's probably somewhat cheaper too,
>
> Let's see one module 4 coils vs
> 8 coils and eight drivers
> Not in the above

Yes, and it's probably even worse on a V12. However, a distributor is not
exactly a cheap part. There must be a threshold somewhere and it's
definitely cheaper on 4cyl engines. However, the most economic is probably a
WS-DIS setup, as it is found on many production cars nowadays.

> >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.
>
> anti-turbo-lag
> I switched parties I'm pro turbo excitement.
> and leaning toward turbo-anti-lag

...great! How are you going to do your anti lag system?


--Axel





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