Ignition Only

[Axel Rietschin]

----- Original Message -----
From: "Shannen Durphey" <shannen at grolen.com>
> > 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.

Sufficient voltage is precisely the main problem overcomed by a DIS setup.

>  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.

I was not aware of this potential issue and I don't believe it happens in
practice. First, why only at high rpm when you have the most spark advance
thus the less fresh gases in the cylinder, if any at all? If you use such a
radical cam and highly tuned exhaust manifold as to fill the cylinder with
enough fresh gases to be ignited, some 30 or so degrees BTDC, consider
upgrading to a coil-per-cylinder setup. Also, at that particular moment, a
significant part of the fuel will probably still be in liquid form thus is
is very unlikely that the super-lean, very-diluted (by burned gases) low
pressure and low temperature (due to pressure drop and partial fuel
evaporation) will ignite at all. That said, you never know :)

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

By far not as much as a coil-per-plug setup, which is also "DIS".

--Axel


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