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Just what is involved in a USDM ST185 3rd gen JDM swap?

PostPosted: Sun Sep 01, 2019 6:24 pm
by EvilStig
Asking because 2nd gen motors seem to be especially rare here now, but there are still some importers who seem to be bringing in JDM ST205 motors.

I am assuming I will likely need to use my original wire harness and modify it for the JDM ECU... what else? do the engine mounts, transfer case, etc, just bolt right up? Do I need a different MAF or other accessories that might not come with the motor? Just looking for options....

Re: Just what is involved in a USDM ST185 3rd gen JDM swap?

PostPosted: Mon Sep 02, 2019 8:13 pm
by Magroo
I havent done the swap and I'm going from memory from what I've read, but it seems to be pretty straight forward.

If using st185 harness and st205 jdm ecu you'll need to move some wires around.

If you have air con you'll need to use the st185 compressor because of the way it interacts with the ac amplifier. I think it has something to do with the rpm signal. This im a bit fuzzy on.

Not sure if the st185 maf will work with the st205 ecu. It might? But it might also cause the car to run rich or lean.

Re: Just what is involved in a USDM ST185 3rd gen JDM swap?

PostPosted: Tue Sep 03, 2019 5:37 pm
by alltracman78
It's cake.

Mechanically everything bolts right in. Transmission, engine, compressor, alt and pwr steering pump all have the same mounting points.
Hardest thing mechanically is the intercooler. It won't quite fit under a regular ST185 hood.
You'll have to find somewhere to mount the water pump and heat exchanger.
If you use a FMIC you can ignore all that.

Wiring is pretty easy too, especially if you have a 92/93 harness. Then there's only 5? wires to swap. Use the EGR wires for the MAT sensor. All the sensors use the same connectors except the MAT sensor.
You don't use a MAF, the 205 uses a MAP sensor. But you can't reuse the one from the 185. You need the 205 one.
You'll need to ground 1 wire at the ECU for the IC level sensor.
You will also need to build a simple circuit to prevent an IC pump code. This is the only "difficult" part of the swap. Not that bad though. 3? resistors and a relay? Can't remember off the top of my head. Or you can use an MR2 ECU.

The AC problem is more involved than just the compressor. I've never dug into it. It should still work except for the idle up IIRC.


As far as you looking for a US spec engine, mechanically all four years are the same. The differences are in the harness, knock sensor and ECU. And the breakdown is 90/91 and 92/93. Not 91 - 93.

That's all I can remember off the top of my head right now.

Re: Just what is involved in a USDM ST185 3rd gen JDM swap?

PostPosted: Tue Sep 03, 2019 5:38 pm
by alltracman78
And you need the 205 igniter. May be other cars that work also? 6th gen 5sfe?
185 won't work.

Re: Just what is involved in a USDM ST185 3rd gen JDM swap?

PostPosted: Tue Sep 03, 2019 6:48 pm
by underscore
If everything bolts up like alltracman says I'm guessing you could just use the 3rd gen shortblock with the 2nd gen ancillaries/wiring/etc.

Re: Just what is involved in a USDM ST185 3rd gen JDM swap?

PostPosted: Tue Sep 03, 2019 8:22 pm
by EvilStig
Thanks for the input.

I already have an ST205 intercooler core and WTA intercooler setup with the RC hood and bumper, so fitment of the IC shouldn't be a concern. I can also wire up the level sensor, although I'm using a generic bosch water pump so idk if that part would work with the ECU. Both my current motor and the new one have A/C pumps. My 185 AC pump is brand new so if that just bolts right up I can swap it.

As for the MAP sensor, how hard would it be to obtain that part and mate it up with the 185 intake plumbing? The 205 motor does not come with anything upstream of the turbo as far as intake, and I'd need a "stock" setup to pass emissions here (or at least it has to look it and perform like it).

Alternatively, might it be easier to use the ST185 RC ECU with my harness and accessories in place of the 205 RC ECU?

Finally,

My alltrac comes with ABS, power steering, electronic cruise control, automatic climate control, and all that other fancy stuff... would there be any issues using that with a 205 ECU?

EDIT: Okay maybe dumb question but I see a lot of 5th gen Caldina engines for sale, newer, and a lot cheaper than the 2nd/3rd gen... is there any reason not to go that route instead?

Re: Just what is involved in a USDM ST185 3rd gen JDM swap?

PostPosted: Wed Sep 04, 2019 4:01 pm
by alltracman78
underscore wrote:If everything bolts up like alltracman says I'm guessing you could just use the 3rd gen shortblock with the 2nd gen ancillaries/wiring/etc.


Why would you want to use just the short block? That's loads extra work for absolutely no gain. Any harness work is much less than removing and swapping heads..

Use the whole 205 engine along with the alternator because it's higher output than the 185 alternator.
If you don't feel like a mess reuse the 185 pwr steering pump and compressor.

But yes, you can use the 185 harness. It's a little ghetto unless you cut into the harness ( that's a discontinued part) but you can add in jumper harnesses for the few things that don't directly bolt up, like the MAT sensor.


You don't need to wire in the level switch, just ground the switch wire at the ECU. Much easier.
That is the exact same process for the 185 RC ECU.

I'm not sure how complicated wiring the Bosch pump to defeat the code would be, if you even could. The resistances may be different.
Much easier to build the circuit.

The MAP sensor hopefully came with the engine. If not you'll have to buy one somewhere. One from a 3rd gen MR2 will also work.
It attaches the same place the 185 one does, physically looks the same too.
It reads manifold pressure, not airflow, so it doesn't go in the intake tract.

The RC stuff would probably work, but you'll most likely lose some power; the 205 engine has lower C:R than the 185 engine.
It's not hard at all to do the 205 stuff.

Yes, all extras work fine. They're not as linked as they are in newer cars.

The wiring is going to be harder. You can't easily reuse your 185 harness?
You can't just bolt in your IC to a 5th gen engine, it's a side feed manifold. I don't know how close the IC will bolt into the 4th gen. Possibly bolt right in?
I assume you already own a 3rd gen?
The exhaust manifold and turbine are 1 casting. Much harder to mess around with the turbo. However IIRC you can swap a 205 manifold on.
Other than that, not really.

Re: Just what is involved in a USDM ST185 3rd gen JDM swap?

PostPosted: Wed Sep 04, 2019 4:51 pm
by underscore
alltracman78 wrote:
underscore wrote:If everything bolts up like alltracman says I'm guessing you could just use the 3rd gen shortblock with the 2nd gen ancillaries/wiring/etc.


Why would you want to use just the short block? That's loads extra work for absolutely no gain. Any harness work is much less than removing and swapping heads..


By short block I mean the sealed block and head assembly. The manifolds and anything not electronic could be left on too. Though if the engine is out of the car I'd be doing a headgasket and studs (along with other seals) just because it's cheap and easy to do.

Re: Just what is involved in a USDM ST185 3rd gen JDM swap?

PostPosted: Wed Sep 04, 2019 7:51 pm
by EvilStig
alltracman78 wrote:I assume you already own a 3rd gen?


To clarify, I have a 2nd gen with an ST205 IC swap. The 205 IC core level sensor is currently wired into an LED indicator light in the cabin, but could be easily re-wired into the ECU, hence I figured I'd go that route.

I have my eye on a local importer who has an ST205 motor in stock which I am considering buying, although it's about twice the cost of the newer caldina motors... I would want to keep my current IC and CT27 turbo, so I guess the 246 motor is out.

I'm currently comparing quotes for a full rebuild to that of the 205 motor...