Gen 2.5 3.8 Swap


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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.

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Looking for that thing i just had in my hand...
Good to see this coming along, makes me want to get my VVT-i swap done.


Looking for that thing i just had in my hand...
Anyone keeping track of what swaps have been attempted, success / failure? Maybe should be a new thread....

I've seen a lot of trucks stall in an attempted swap, ones that others have before completed. One of my friends has a 4G54T swap that is like 98% complete and has been for a decade.


Looking for that thing i just had in my hand...
Hopefully JBFP will read this and crack the whip on his lackeys to get it done.
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I have been slowly working on the rig and had been fighting coolant leaks on the back of the heads and crossover tube, but its up and going. I got the tune good enough to get me down the road for a road tune. This thing runs good and and is getting better and better. A lot more power!!! I wish I had an timing table for the 6g75, I am trying to figure it out from scratch.


Well-known member
This I expect is a bit of a history piece since it is a swap done long ago. In 2005 I bought two non running 1995 SRs from the dealer I worked with. Fun part is the dealer is a 10hr round trip from me and these are heavier than I chose to tow behind my Mighty Max. So it cost me a bit in favors and money to collect them.
Once I got the first one here I looked it over and made my plan. This had just had a belt failure and the work order was estimated right about $5K, customer just walked away.
Since I can not leave anything alone I chose to pull the engine out, nothing was wrong with the bottom end but I looked around online and bought a very young Galant 3.8 from a yard in Chicago area. I also bought a bunch of valves and guides and got to work on the heads. I have all the tooling in hose for this work.
Once the engine arrived I pulled the SOHC heads and set the DOHC ones in place. This allowed be to scope out the differences in T belt which being the tensioner is different between engines the original 3.5 DOHC belt was not an option. But interestingly enough, the considerably shorter 3.0 DOHC belt was spot on for what was needed.
One thing I needed to make a decision on, the Montero DOHC engine has dished pistons, the Galant 3.8 has a mild pop up. This will be interesting. So as I started setting up to CC the chambers and pistons I decided, F-it and just build it. So that is what I did.
Normal for me, the heads and manifolds get the ports cleaned up and matched. Here are the parts being trial fitted.


Well-known member
What this build is parts wise,
The 05 Galant engine had the Montero oil sump and water pump swapped over. I do not recall if I utilized the Galant or Montero WP itself since the diameter of the belt sheave varies on the V6s.
The later style tensioner was retained since they tend to offer a more reliable T belt life.
The Galant crank sensor utilizes a multi tooth wheel and different type sensor. The sensor is also located differently. I found the early style sensor mounted up fine and there are a few different shutter wheels of which one was just right for this.
Up on the top side I used the new style injectors which are shorter than the old ones. I used the Montero fuel rails and machined shorter insulators such that everything fit up properly. I did make a fresh injector harness since the connectors are different.
Other than differences in radiator hoses since I build my own radiators nothing else was changed.
At this point, I installed the engine and fired it up. No other tuning has been done, nothing was needed.
The only thing in the near 15 years I have been driving this I would have liked to do is to tune the transmission, this is something I did with my turbo Gen 1 which made a major difference for that swap.

The outcome of this swap, It is coming on 15 years and just under 100k miles since I built this. I have changed the oil a number of times. The filter is a PIA since it is snug to the diff cover. and just recently due to damaging and plugging the exhaust from backing up in nearly 4' deep snow I had do change the spark plugs. Otherwise they were original to the Galant engine.
Going forward, this is not in active use due to frame rust where the trailer hitch mounts. The rear diff housing leaks oil due to rust such that I can not trust the epoxy sealing it on long drives.
Not just sure what direction I will go. I would like to buy a 2.5 to swap this engine into. I doubt I would do more to the engine than a new T belt and possibly valve seals.

What has this engine been like to live with.
It makes power, how much I have no clue. Driving other peoples DOHC SRs this thing is a similar step above them like the step from a 3.0 to the the 3.5 DOHC is.
Open the throttle at low speed, this shoves you back in the seat hard, it slams up to 3rd a bit over 70 which is right about 7K on the tach.
This has you pressed back in the seat passing through 120 as well.
Gas yardage is better than I hear others speak of in Monteros. I have seen 20ish on long hauls. 15-17 around town which is a mix of hilly gravel and windy roads with some 50-60 open road mixed in.
Pulls trailers fine but would be better if I tuned the transmission for the higher torque. It just shifts or kicks down needlessly. Cable adjustment helped but not as good as it could be.
I wonder what this engine would be like in a car?
I have been slowly working on the rig and had been fighting coolant leaks on the back of the heads and crossover tube, but its up and going. I got the tune good enough to get me down the road for a road tune. This thing runs good and and is getting better and better. A lot more power!!! I wish I had an timing table for the 6g75, I am trying to figure it out from scratch.
Can you use the rom from a 3000GT, diamanté, or Montero?


Nice to see this thread is still alive. I do wish, however, that more people would explore the supercharger route. M90's are still cheap (under 250 bucks) and plentiful. And at low boost, neither fueling nor intercooling would be an issue (there are several ways to piggyback extra fueling outside of the ECU, and you could add an IC or water/meth if you wanted to).

For me, the hard part is the mechanical side - fabbing up brackets and inlet/outlet pipes. I still feel like this is 1000% the cheaper, simpler, and more powerful option. I just dont have the wherewithal to tackle it alone. :/


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I have been daily driving the montero with the 3.8 Mivec and have clocked about 8k miles with no issues yet. I have still yet to upgrade the exhaust and plan to go with a catless 3". I also want to redesign the intake manifold for something better flowing and have been toying with the supercharger idea. As a daily driver, I have been messing with the tune to get better fuel efficiency, but 11-12mpg is the best I've seen. I also have burned up the Mivec solenoid a while back and haven't gotten around to replacing it. Megasquirt has very good VVTI control, but doesn't control in the way it was meant to for Mivec. There's no good way to give full 12v for 2 sec, then pwm after that.


Glad to see several of you guys doing similar builds. I’m still running mine and dialing in the tune more and more. Mixed driving is around 18-20mpg in my Mighty max.
I must admit that I’m having a hard time keeping tires on this truck. Lol.

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