Spark timing

[Andy Wyatt]

G'day all,
I'm fairly new to this news group, I've been lurking for about a week, and
I've got a question about ECUs in general. I'm currently building an EFI
computer for my 83 Pusar Exa turbo, and have the fuel running great,
currently I'm working on spark.

Question is: How do most ECUs for turbo cars handle spark timing? My car
does not have a MAP sensor as standard, so it could only determine by
airflow/rpm. It also doesn't have a throttle position sensor, just a switch
which closes when the throttle is fully closed. Do they just have a lookup
table (map) as for fuel? Or do they have a certain amount of base timing,
then an algorithm to determine centrifugal advance and vacuum advance/boost
retard? There is nothing in the Nissan manual about it; all it says is that
it runs 15 degrees advance at idle (pretty high, I thought). Would it be
less during cranking? Anyone ever mapped ignition timing for a 1.5L turbo
engine?

Also, is there any advantage of sequential injection over group fire other
than the increased atomisation you'd expect from injecting the fuel while
the air is flowing through the inlet port? I heard someone tried swapping
the injector leads from a sequential injection engine around so they were
all wrong, and dynoed it to find there was no difference in power output,
just in emissions at idle...

Any help would be greatly appreciated
Andy W :-D