Re: Lt1 Optispark

[Scott Knight <scott@scottknight.com>]

> > The optispark would probably be the hardest to do IMHO.  sorting out all the
> > differnent signal lenghts would be a trick.  To me it would be easier to use
> > an existing Dissy, and add another sensor, for the sych sifgnal.
> >
> What about putting the trigger on the crank and setting the dissy up
> only for the sync signal.  This would give you TDC driven by the cam.
> If the sync has some minor time shift it shouldn't matter as long as
> it's after the last cylinder and before the first cylinder.

FWIW, I am getting ready to run a DIS system on my 396" with the SEFI8LO
driving a Northstar module.  I have a few pages of the shop manual from
a '93 Allante that outline the Northstar DIS system used there, and it
looks like it would be difficult to gin one up to work from scratch
unless you were really going to do some heavy duty fabricating and
signal processing on your own.  Until I looked at the manual, I assumed
the PCM did the work of telling the coils when to fire, but it is
exactly the opposite on that system.  There are 2 crank sensors and a
cam sensor that directly feed the module which in turn spits out a bunch
of data to the PCM and receives timing info from the PCM.  It is much
more complicated than I thought it should be (but then the Opti Spark is
as well).

Fortunately, the '96+ LTx engines have a factory CPS (crank position
sensor) that produces the exact signal that the Opti Spark sensors do
(5VDC), so I can just use it to trigger the SEFI8LO.  If you were
diligent, it would not be impossible to reproduce the crank signals that
the Northstar module is looking for with a couple of these sensors (weld
in a new one 27º away), and a slightly modified Opti wheel.  Not sure
how to send it timing info though.  This could be a difficult and time
consuming project, but seems worthwhile if you don't want to spend $2k
on a SEFI8LO to drive it.

Quickly looking over the LT5 DIS system scans that were just posted to
the ftp site, it appears to be a bit simpler than the Northstar.  Only
uses a single crank sensor (must be LT5 was batch fired EFI?) and synchs
up with the arrival of either #1 or #6 cylinders' triggers.  I am not
sure why Speed Pro didn't go with LT5 modules instead of Northstar other
than the fact that there are a boatload of the latter available and the
LT5 modules are very expensive.  This would appear to be a bit simpler
and less time consuming to implement than the Northstar, though still
challenging and quite a bit more $$$.

That is about all I know at this point.
-- 
Scott Knight  mailto:scott@scottknight.com
http://www.scottknight.com/ IRC:SS396man
'95 Black Impala SS
'94 Ducati 900SS CR
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