Adjustable electronic ignition

[Craig Pugsley]

> 
> Just a quick question,
>                                 My Holden Commodore runs a Buick 3.8 litre
> V6 and uses a crankshaft sensor for the ignition timing. What I want to do
> is vary the timing, preferably from inside the car. One way to change it,
> although being non-variable, would be to offset the sensor slightly to
> obtain a fixed advance or retard in the timing. What I would prefer however,
> is to intercept the signal before the ECM, and somehow modify it
> electronically to make it appear that it is advanced slightly. 
> 
> Can I do this with a simple capacitance type delay, or would I need to use a
> specialised circuit? Also, any ideas what the delay would have to be -
> milliseconds, nanoseconds ? Ideally I would like to have some sort of dash
> mounted box with an adjustable dial or something along those lines.
> 
According to the info I have (for a VN 1988 commodore with 3.8 V6 and GM
P3 computer), there are 2 hall effect devices near the harmonic balancer
that read pulses from 2 seperate rings. The outer ring has 18 pulses of
equal spacing and the inner ring has 3 un-equal length slots & the
computer counts how many of the 18 pulses occur in the length of the
un-equal pulses to determine where the engine is. (It doesn't need to
know if the cylinder's TDC is for the compression or for the exhaust stroke
as it uses a wasted spark system).

What this means is that electronically adjusting the timing would
require microprocessor intervention, NOT a simple capacitor etc delay.
you MIGHT be able to fool the micro by clocking the 3 pulse set into a
FIFO device, and bump up the clock rate momentarily to get advance etc.
but if you break your crank don't blame me.

You might be able to do it by the fixed mechanical advance idea and letting
the knock sensor tune to computer properly. (& this would be a LOT
quicker & simpler to try)

I am wondering why you want to do this anyway? I think the extra power
you might gain would be less than if you used premium unleaded or a
good exhaust system.

Cheers,
Craig.

PS any suggestions for a good source of automotive connectors?