I was aware and following the progress of that now pretty dormant thread in the past, although much of the discussion took place when I was in "exile"!

I'll just post a thought or two here regarding that project.

Dedicated multi-trace PC based O-scopes can be had for around $100-200 on eBay, there are numerous 5 trace scopes available, the frequency range occurring around these engines is quite low and any of these cheap scopes should be able to easily capture and present waveform data.

From a design standpoint regarding developing an instrument one way I would look at it from a perspective where I would try to make use of the physical/mechanical circumstances and avoid making use of the electric/electronic circumstance that are inherent to these engines. Identifying, quantifying, and some how adapting the signals will probably be somewhat challenging.

For instance with respect to the balancer pin as the TDC indicator, the OE system uses a Hall Effect detector, rather than sort of tap into and acquire that signal, and then translate it to some other usable form; it might be a better solution to instead create the signal directly in the form you need. One way might be to locate a stand alone detector/signal generator and swap it out for the OE sensor to do any testing, alternatively an add-on sensor/signal generator could be located in a different position say 180 degrees opposite the OE, you might fabricate a bracket that could easily attach to some hard reference points that would allow the sensor to be positioned correctly. The 180 phase difference could be accommodated electronically or through some other signal conditioning or the balancer could be drilled and tapped for a second pin that would be installed for testing purposes.

The signal could be generated through different technology also, instead of using Hall Effect technology; I think that because of the physical circumstance a photo-interrupter may be a good candidate. Photo interrupter modules incorporating an emitter and detector arraigned across a pre-defined gap are readily available. Something like that could detect the pin as it passes through the detector modules gap, again this could be mounted as a substitute or in an alternative location. Now the photo interrupter would probably be less than idea for a permanent installation because it would be susceptible to dirt degrading its operation, if one where mounted to a bracket which in turn could be held in a specific predetermined position maybe even by a couple strong magnets say, to be use only when doing testing it could work pretty neat!

Nowadays it should be relatively easy to find an IC that will drive the sensor and output an appropriate signal. Electronics have become to some extent modular building blocks, often times a sensor vendor will have exemplar compatible drive circuitry available in its application notes, and IC manufactures very often do the same showing their IC with a sensor and any related necessary components to generate specific outputs. National Semi- Conductor used to publish volumes of application date for the wide array of chips they offered. Today there are probably programmable micro processors with onboard A/D converters that can accomplish serious signal conditioning.

Just for fun check out STAMP and PIC micro-processors, in fact that is what techguy512 of this forum used to implement his programmable tach amp replacement.

Nowadays once the signal acquisition and waveform generation tasks are addressed it's only a short hop, skip and a jump to adding a Bluetooth interface and a Smartphone app where someone could watch what the engine was doing on there Smartphone as the drove along, and simultaneously record and archive that to compare over time!