If you wanted to stick an old 300TDi motor and manual box in it, do away with the ABS, EAS and probably the BeCM and run all the electrical parts directly from the switches, probably anyone could do it. But all you would be doing is recreating a mid-1980's Classic in a P38 body.
It always makes me laugh when you see people posting up 'how can I bypass the BECM' or other related 'how can I get rid of it' posts... If you want a vehicle without the "complication" of the BECM, or something you intend to drown on a regular basis... leave the damned P38s alone and stick with the more simpleton-friendly old Discos or Defenders...
Did see on one of the Facebook groups a while back someone had run new wiring for all of the windows to control them with rocker switches... and then asked 'how do I clear the window not set messages'..........
I have been watching this with very keen interest as well. I looked at it a few years ago but thought better of it.
I have had a checkered history with engine swaps over the years. Norton with a Vincent engine, Ford Pop with a GT Cortina engine, Ford Escort Mexico with a 2L engine, Mini Cooper with a full race engine, then Range Rover Classic with a 3.8L Perkins diesel. It has put me off a bit. Nothing fits with most swaps.
A few comments off the top of my head:
The M57 engine is based on the older M51 engine, that we know. I also know the M57 will bolt straight up to a 4HP24 gearbox using the p38 diesel bellhousing. Not sure then which starter motor and flywheel are used, M51 or M57? or are they the same?
The problem with this is that only the diesel torque converter will fit. The petrol TC's are too big.
An option is to fit an uprated p38 diesel torque converter. I had one fitted by Ashcrofts to my car. Not cheap though.
I have chipped my M51 diesel and fitted a larger intercooler. Power has gone up from 135bhp to about 190bhp. I have also got the 4HP24 box fitted. It copes OK but would the TC cope with 300 bhp? I suspect not.
Question .... will the M57 TC fit into the p38 M51 bellhousing? I don't know.
I also had a look at the Compushift gearbox controller when I was at Ashcrofts a few years ago. A member on the .net site had one fitted to his p38 which had a 2.8L South American made diesel engine. Gear changes were very harsh.
A diesel engine with its long stroke and high compression ratio puts out a lot more torque and the fuel mapping has a Torque Limiter map specifically to cut the power during a gear change. The engine ECU needs to speak to the gearbox ECU in order to do this. If it doesn't it will result in harsh changes and even see off the gearbox.
I have also seen a p38 TDV6 conversion locally. Mechanic used a manual box though. Said he would never do another one.
I much prefer the straight six M57 engine.
Honestly at this point in the morning I'd need to look it up again, but I believe I will need an adapter plate for the bell housing I already have, because I want to retain the large torque converter that will keep the stall speed a bit lower than using the small diesel one. I won't be pushing for silly power - though about the 250hp mark would be nice.
Torque as you say may be the lunching factor in the gearbox long term. Standard I think the engine is rated for 390. The HP24 I think is good for 450, though from posts I've seen Ashcroft's believe it is okay for more if it isn't hooned about constantly.
In terms of gearbox control, having the torque reduction request working is on the 'must have' list - if it doesn't drive properly its no good. I want to stay away from the Compushift though as I haven't seen any reports of it 'just working' smoothly. Until we've exhausted the possibilities for getting the Bosch/Thor auto ECU working over the CAN data (with or without fudging if required), I won't be looking at one.
Last night didn't result in much success. We were attempting to feed a simulated road speed signal into my bench BECM+instrument cluster (as if it were coming from the ABS ECU), which would then be fed to the M57 ECU to see if it matched up okay. At the same time, the engine speed output was connected to the BECM to see if it would drive the tacho etc properly.
Neither worked, beyond the tacho jumping occasionally.
As it transpires, my BECM is from my old 96 P38, which had the GEMS engine. The engine speed input is PWM, but 0-12v, whereas the Thor is 0-5v, and my Arduinos as standard only spit out 5v - so that likely answers why that didn't work.
I had also tried the output from the M57 ECU, as we know we can make it think the engine is spinning by simulating the crank and cam sensors (pictured previously). But it turns out, its engine speed output is on a totally different connector pin from the one I was latched on to... I've been looking at so many different diagrams and pin outs lately I must have confused two of them. I suspect its also a 5v signal, and it was late so I went to bed!
As for the road speed signal from the ABS ECU, that looks to be 0-12v too on all model year P38s. So tonight armed with some more tweaking, both signals will hopefully be fed in and we'll see the dials do their thing, and the engine ECU will hopefully spit out road speed over the CAN bus!
Or something like that.