Gen 2.5 3.8 Swap

[Swank Force One]

I have a 98 Montero (gen2.5). Motor mounts shouldnt need modification. The aussies have the mechanical side of the 3.8 swap ironed out pretty well.

I'm not real interested in running a Mivec motor on a window switch.

So the SL ecu and a couple wires gives me working knock to go with a late 3.8 sounds easy enough. Then just have to find someone to flash the ecu? Thanks!

 

[ChargerX3]

I feel you are underestimating the complexity of this swap. Also not all configurations of the 6g75 are the same. That includes motor mounts and their bosses.

 

[Swank Force One]

I feel you are underestimating the complexity of this swap. Also not all configurations of the 6g75 are the same. That includes motor mounts and their bosses.

I feel like i'm missing something... are you saying that Mitsubishi took the time to make entirely different blocks for different cars that were all called 6g75s? Every single thread i've been able to find concerning a 6g74 --> 6g75 swap says "use your gen2.5 motor mounts, they bolt to 6g75," which is the only reason this swap is interesting to me. I've done a motor swap or few in my time, the electronics were previously the only thing that worried me about this, since typically i just go straight to a standalone, but i'm not interested in doing that in this truck.

If the mechanical stuff isn't actually straightforward, then there's really no point in sticking with the Mitsubishi family at all for me. What am i missing? There's been dozens of 6g75s swapped in Gen2.5 Monteros, but there's been some concern about running them on the stock unflashed ecu, which is why i was following this thread. If the ease of this swap mechanically speaking that's been communicated is incorrect, could you please elaborate?

 

[ChargerX3]

Yes I have seen variances in the blocks. Heck there are quite a few configurations for the 74 alone depending on what year and on how it's mounted in the engine bay. Best to do your research ahead of time.

It can be done and easier that other builds out there but you will have to research it out.

 

[Swank Force One]

That's what i'm trying to do. Every thread but this one says grab any old 6g75. Most threads have concerns about running the motor properly.

This thread is the only one that does anything about it, there is nothing else out there in my hours of searching that addresses running the new motor "properly," which is why i'm asking the questions i am in here.

There's far more information about V6 swapping a 93 Ford Escort than there is about this should-be-easy swap.

 

[ChargerX3]

Sadly I don't have all the 6g75's in front of me or at my disposal, so I can't solve your dilemma. It will work but you will need to research your specific application. It sounds like you have done motor mounts before so you should be up to the challenge. I had to weld a boss onto my passenger side block to get it to work. Yours may be different. The divers side I had to weld iron onto the mount to make it sufficient to support my anticipated load. Again if you are confident with welding, and cutting a little then you should be ok.

If going 75 go MIVEC. Just about as easy to find as the non and your gains are much more. You will regret putting in all that work just to find yourself wanting more.

 

[Swank Force One]

Sadly I don't have all the 6g75's in front of me or at my disposal, so I can't solve your dilemma. It will work but you will need to research your specific application. It sounds like you have done motor mounts before so you should be up to the challenge. I had to weld a boss onto my passenger side block to get it to work. Yours may be different. The divers side I had to weld iron onto the mount to make it sufficient to support my anticipated load. Again if you are confident with welding, and cutting a little then you should be ok.

If going 75 go MIVEC. Just about as easy to find as the non and your gains are much more. You will regret putting in all that work just to find yourself wanting more.

I'd love a MIVEC, but the electrical side of things i'm not real excited about. Is your window switch just set up as on/off at certain RPM and then you manipulated the fuel/timing maps in the 3000GT ECU to compensate for MIVEC behaving in a manner that it doesn't in OEM form?

 

[ChargerX3]

Bingo.

 

[Swank Force One]

Does it FEEL smooth? Or has it turned into more of a stereotypical "vtec" thing?

 

[ChargerX3]

If you ease into 4K rpm you can feel it. Otherwise it just feels like the engine likes to gobble up the rpm from idle to the top. It's not overly crazy. Then again I have a long manifold runner so I know that is killing top end.

 

[Atrais]

If you ease into 4K rpm you can feel it. Otherwise it just feels like the engine likes to gobble up the rpm from idle to the top. It's not overly crazy. Then again I have a long manifold runner so I know that is killing top end.

But dat torque tho...

 

[ChargerX3]

An SR intake manifold with dual runners would resolve that issue. Maybe...

 

[Toasty]

An SR intake manifold with dual runners would resolve that issue. Maybe...

Or a 3.8 variable intake? I was thinking about swapping one onto my 3.5 for some added grunt.

 

[ChargerX3]

Or a 3.8 variable intake? I was thinking about swapping one onto my 3.5 for some added grunt.

Bingo. That one would be the best fit. I'm just not finding any available.

 

[94montySR]

So i have been working on this swap for the last couple years and the project got put on hold for a while. I am back at it and finally got it fired up a few days ago. I sill have a bunch of odds and ends to finish before i can drive it. I have a 1994 SR that I put a 2008 3.8L Mivec in (69k miles on the engine for $900) . The engine directly bolts up to the transmission and motor mounts. I had to use the oil pan, timing covers, and thermostat housing from a 3.5 SOHC. While i was in there i put in a new oil pump, timing belt, and water pump. For the lower intake manifold, i also had to use one out of a 3.5 SOHC montero sport. The lower intake manifold on the 3.8 had square ports and the sport had round which mated up to the SR upper intake manifold. Since i couldn't use the factory 3.8 lower intake, i then couldn't use the injectors and fuel rail either. I used a fuel rail from a 3.5 SOHC sport, then used toyota camry injectors (320cc) which fit perfect. The upper intake manifold did not clear the valve covers, so i took the gasket and had a 1/4" spacer plate made at the machine shop to raise the manifold up. The SR exhaust manifolds bolted right up as well. Fuel and ignition is being controlled with an MS3PRO EVO while leaving the factory ECU in place to control everything else on the vehicle. I am to the point now where i got it fired, so now i need to clean up wiring and figure out what all still works and what doesnt work on the rest of the vehicle. The factory ECU took inputs that are no longer there and shared them with the transmission and cruise controllers. So i may need to share some inputs from the megasquirt to the oem ecu (TPS, RPM....), we will see. I will then have fun controlling the variable intake along with the MIVEC, should be interesting.