Aha! If your 4ZC!-t came standard with an optical dizzy, it must've had the I-TEC ECU.
For some reason, the Australian 4ZC1-t came with a typical mechanical distributor - a governor & vacuum advance (yet the ignitor was linked to the knock sensor or ECU).
I've always been meaning to find out if other 4ZC1-t Piazzas had the optical.
As to why we recalcitrated to a mechanical dizzy - and a JECs copy of the Bosch Jetronic ECU - AFAIK the last valid conclusion is that GMH "couldn't handle" the all-electronic I-ITEC. (That must have added a reasonable cost to the Aussie Piazzas LOL.)
I'm reasonably sure the 4ZE1 & 4ZC1 (& 4ZD1) dizzies are physically interchangeable. (The 4ZB1 isn't - it has a different hole or location. My hero RodeoBob wrote about that somewhere - maybe on here, else holdengemini or ozgemini.)
As to their guts, the G200W DOHC Piazzas also had ITEC with an optical dizzy. (That was in 1980, and we got our mech-dizzy Piazzas SIX years later!).
Though the G200W's optical sensor module is older and has visible components, it is mechanically interchangeable with the 4ZE1
Jackaroo/Trooper module. (But NOT the Rodeo. The Rodeo interface connector is a 4x1 connector that exits out the side. The Jackaroo & G200W Piazza have a 2x2 spade connector that exits out the dizzy's bottom.)
Electrically I see no issues. The electronics merely
pulse the slots and should use the same switching (ie, open collector or 0V/ground/earth/chassis switched - ie, "low" when pulsed).
Both discs have the typical rings of 4 & 360 slots. Any alignment problem would be restricted to its mounting position, but distributor rotation should compensate for that, else remount the disc. (I have samples of both, but they are elsewhere at the moment.)
[ FYI - IMO the 360 slots is why that dual-
row optical system is so good for other ECUs. For those that require 1 & 4 slots, just fill in 359 slots (with liquid paper etc). For other combinations (4-6, 4-12 etc, 2-1, 1-12, etc), fill all but the required slots. And since its locked, rotational direction does not matter.
]
(BTW - good to hear of another Megasquirt. The old
DIY-EFI has gone a long way - though I still think they don't have self tuning?)
So distributor-wise, you shouldn't have any problems.
[ FYI - the RG dizzy: Otherwise.... I can't recall my "RZ" diizzy in a 4Z outcome. The RG dizzy is a (common) G-Z engine dizzy (from our Geminis, and older Rodeos & Jackaroos). Its points and upper rotor are replaced with the reluctor sensor on its bearing carrier, and upper rotor from the early FWD RB Geminis. It can be locked for ECUs and reluctor-sensor output extended. For spark, the RB's internal ignitor can be mounted internally.
The RG (G-Z) dizzy is easily modified to fit
ANY G-series engine - ie, the DOHC GWs, OHV GUs, and Jap SOHC GSs. Hence "we" with inferior and rare GU & GW distributors have a readily obtainable distributor. GZ owners get cheap electronic ignition. The RB's reluctor is the newer robust & superior single-piece system (not the weaker multi-piece & multi-pole systems of the GW, Nissan N13, VL Commodore, JE Camira, etc).
The RB ignitor is also used in other Jap vehicles and with its common "blue"oil-filed Nippon-Denso ignition coil is a ripper. (It operates well below 6V.) Newer E-coils can also be used. Current limiting does not seem to be an issue. I have used Bosch MEC-717 etc coils which have a mere 0.4 Ohm primary resistance - ie, 4x the current of standard RB etc ignition coils.)
]
The 17mm input shaft per se shouldn't make much difference. That is merely the crank-shaft
locator and shouldn't carry any load. However it should signify a generally stronger box.
Early Isuzu boxes (MSA, MSG etc) had weaker 2nd gears - the most common source of synchro & gear wear or failure.
The MUA (TFR etc) boxes fattened their 2nd gears (that info from RodeoBob).
And the later boxes are stronger - as shown by bigger shaft diameters etc in your pics.
Interesting that my TFR box has a larger output spline. However, even the smaller spline has AFAIK a fatter output shaft to the spline. Though the smaller spline will still be twisted by my (hi-torque modified) G200W, at least the fore-shaft has less chance of breaking.
Thanks for understanding those bottom-cavines (bum-steers). I try to add AFAIK &
I thinks when uncertain. But of course, there are times when I'm wrong. Sometimes bad memory. Sometimes finding out about alternatives that I never struck.
You might find my digressions and ramblings a bigger pain LOL!
[eg - the RG dizzy stuff - especially since optical 4ZE1 dizzies should be relatively easy to obtain. At $35, they are worth grabbing whenever a (Jackaroo; else Rodeo) 4ZE1 comes into our local "Pick A Part" wreckers. But as a final fallback, I could resurrect my 1988 flywheel ignition. These days probably using a $3 PICAXE 08, and installed by fitting 2 sensors to the starter motor (the 2nd being redundant - the system monitors both and alerts to intermittent operation) and filing the edge off one end of a flywheel ring-gear tooth.
]
But my ramblings are also for the benefit of other Isuzuans as well as for "our" backup or workaround methods.
Incidentally, my "MUA" box is from a TFR (4ZE1) Rodeo (2WD of course!), though I also have a complete 4ZE1 Jackaroo (all are 4WD).
In my outdated engine & gearbox table, I have the MUA as coming from the Isuzu MU (pre- & post-1992 versions).
The MU became the Frontera and some are 4ZE1 (I think). I might look further in to them. (eg, see
pick-a-part - parts-recovery, select Isuzu and see a 1991 Frontera
at the moment. Normally Isuzus are listed under Holden - ie, Shuttle, Jackaroo, Rodeo, and Gemini (with the RWD "T-series" with GZ engines being pre-1985(?) and FWD RB being post-1985 [Gemini knowledgeable people may correct me]. )
I've intended to hit my shed to measure gearboxes & engines etc and update my docs. That's AFTER I tidy up my house.
I've been tidying now for a few years with little success. I might be tempted to review my priorities. Besides, summer is coming - I should get out more.
Oh dear, another short reply...
IZU069 - ISUZU means a lot to me.
