5th Generation 3SGTE swap into my 1989 GT Hardtop (ST246 engine)

[Post 2]

After dropping the old engine, we set aside picking the bits off that need to be reused on the ST246 engine. Here’s a list off the top of my head, but it’s not exhaustive. Some small brackets and bolts were obviously reused:

- engine hook over the A/C (this needs to be ground down and modified as it will foul on the water pump housing on the new engine, and then some spacers can be used to get it to line up with the engine mount that sits in front of the timing belt cover)

- alternator

- harmonic balancer

- many parts of the old loom if you want to keep the accessories and other non engine things functioning

- flywheel + bolts (as the new engine only comes mated to a lame auto)

- if you didn’t replace the alternator bracket like I did, you need to reuse that too. A small corner of it will need to be ground down to make sure it bolts to block without hitting the intake manifold.

- entire transmission assembly.

- engine mounts (if you don’t replace them. Mine were in good condition)



There are a few things that need to be fabricated or modified to make work:

- downpipe. (The CT15b on the new engine had a different bolt pattern and position to the CT26) there are de-catted ones available from PrimeMR2 and a few other sellers if you don’t wanna get the original downpipe modified)

- new heater core hoses (The new engine’s lines are facing the wrong way. A longer hose can fix this but make sure it’s not kinked)

- the wiring loom. This is a bit of a headache and there are people who you can send the loom and OEM ST246 ECU to, and they will flash the ECU to get rid of the immobiliser and customise your wiring loom to make it work with the MR2. I chose to put a Haltech ECU in so we had to do our own wiring loom and connections. Thankfully Dad is a bit of a wiring nut so that was his main job for the swap.

- Reuse the A/C system. Unbolt the A/C from the block before you drop the engine and hang it from inside. That way the system doesn’t have to be recharged when you do the swap. The A/C will bolt straight up to the ST246 engine.

- some modifications to the fuel line. Pre made ones for this swap are available from TCS motorsport I believe. I made my own.

- custom throttle cable to account for the slightly different position of the throttle body and anchoring point. There are also pre made ones available from MR2 Heaven and Prime MR2. Just make sure you get ones that are compatible with RHD or LHD depending on your model. I made a blunder here and had to do some throttle cable mods to fix up this issue…

- some hose bungs to block off the coolant lines that run to the original automatic transmission oil cooler.

- The throttle body and idle control valve have coolant lines running to them to help de-ice them on very cold days. I plugged these off on the recommendations of lots of mr2 owners that state it had no effect, and I also live in Sydney where it never gets cold enough for them to make a difference.

Okay, time for some photos.

New airbox:



New intercooler:



Modified engine hook:



Dropped the fuel tank and replaced the pump+cleaned tank. The inside was in great condition. No filth or rust. I wouldn’t want to do that with the engine in the way.






New ECU bracket:



New fuel lines+filter:



New clutch (not done up in photo):



New downpipe (it has a support bracket at the bottom that is undone as it is done up when it attaches to the rest of the exhaust)



The finished loom. Took Dad about 2 days to figure it out and test it all.








That’s it for now. Hoping to get the engine in on Wednesday and start it up Friday night. I’ll be back with more!

[Post 3]

Engine is in and bolted up. Some difficult fittings but it all plumbed up nicely. Getting the first two mounts (East&West) was very tricky and needed a jack to help position the engine correctly. The way the engine hangs on the crane means it doesn’t line up perfectly to the side mounts. Once those bolts are through though it becomes quite easy.

I’d also recommend doing the A/C tensioner bracket up before hand as where it bolts to the block is quite tricky with the engine in.








Had some small wiring issues. Had trouble getting the Haltech to operate the factory EFI relay so the pump wasn’t priming when we turned the key.

There was a couple of other configuration conundrums, such as there being no default calibration for the Gen 4/5 3SGTE MAP sensor. This meant the ECU didn’t know what voltages meant what pressure in the manifold. The maths equation that relates voltage to pressure is a linear line so it’s easy to work out the calibration if you have a working sensor and a way to apply pressure and read voltage from the MAP.

If anyone needs the Haltech calibration data for a Denso MAP sensor 079800-4310 send me a message and I can give you the file.

I have to say I’m quite happy with the intake system. The intercooler kit and the racer x air box fit very well! No issues there, although it should be mentioned the turbo to intercooler pipe comes very close to the dip stick, but should clear it.

Other than that the timing was easy and the rest of the wiring and calibrating went smoothly.

Hoping to get the electrics sorted out on Sunday and fire it up!

[Post 5]

Another quick one.

We think we diagnosed the alternator issue, and it’s as simple as the alternator appears to be dead. We shorted Pin 4 on connecter EA3 to ground with a wire while the alternator’s plug is disconnected but the with the positive cable still bolted on. The battery light came on in the dash which apparently means it’s dead according to electrical diagnosis wizards.

The alternator was working as far as I’m aware before the head gasket went. But it appears to be the original one so it would he due for a rebuild. The car sat for about 5 months only getting turned over twice, mix that with a good clean (only using brake cleaner mind you, no water) and the engine removal it’s possible that was enough to knock the remaining life out of it.

We removed it tonight (the racer x alternator bracket made this a breeze) and I took some photos. Keep in mind this alternator is probably as old as the car and it has been given a massive dousing in brake cleaner prior to being put back on the engine.

It’s been sent off to get rebuilt now.






Also, figured out some other dash issues. The factory boost gauge was stuck at the top and that’s because when I wired it back into the new loom it was accidentally supplied with 12V and not 5V…. So it may be dead. I’ll deal with that later, but it’s an easy part to replace and easy wiring fix.

My ABS sensor was also on. And that is most likely because we started it up on engine stands and the ABS computer did not like that the rear wheels were moving slightly and the front’s weren’t. I haven’t tried it yet but apparently the fault will clear if you disconnect and reconnect the battery.

The last one is the tachometer. I may need to play around in the Haltech Elite 1500 to see if the tachometer pin can be set to provide the correct signal as the tach needs a signal that has something to do with the distributer and igniter which I no longer have on the car. I believe there is a setting on the ECU that can mimic this, but failing that there are tach adaptors or resistor hacks you can do to trick your tach to read correctly.

I’ll be back with updates soon!

[Post 7]

Quick update, took the car for it’s first drive tonight. I haven’t had it tuned so I stayed off the boost and never went more than 30% throttle but the low down torque and power is immediately more noticeable.

The CT15b turbo is very spool happy and I could tell it was just waiting to go. Looking forward to the dyno and tune to see how it really feels.

The sound of the GFB TMS respons BOV is unreal. Played around with it’s wastegate spring and mixing between the 100% vent and 100% recirc and it sounded awesome. Loads of turbo whooshing noises and even a small bit of flutter off the throttle. Heaps of fun.

Side note: the alternator issue I mentioned previously was not fully resolved and there were some charging issues still with low voltage. Turned out to be an earthing issue. Not sure if that was a result of the light weight bracket, engine paint or a combination of other issues but we ran a 4 gauge cable off a bolt on the alternator housing to the engine block and a new cable from block to chassis and the alternator started charging about 14.3V at idle. Solid.

Make sure you earth your car properly!