Adjustable electronic ignition

[Adam Tate]

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.

All input is most appreciated.

Adam Tate.
[at at multiline.com.au]
http://www.multiline.com.au/~atate/index.html