My Complete Experience Swapping a 3RZ Engine into My Lj71G Prado (Auto Transmission) — Seeking Advice

[rakan100]

Hey everyone,





I wanted to share my full experience with my Toyota Prado LJ71G (1993 model) after swapping in a 3RZ-FE engine, and I’m hoping to get some advice on the challenges I’m still facing.





Background:


My Prado originally came with a 1KZ-TE engine (turbo diesel) and an automatic transmission. The vehicle is a Japanese import, and I had already converted it from right-hand drive to left-hand drive before the engine swap. Wanting more power and reliability, I decided to swap in a 3RZ-FE engine while keeping the stock automatic transmission.





The Swap:


The 3RZ fit in fairly well with some custom mounts and wiring work. I was hoping for a noticeable increase in torque and overall performance, and while the engine runs fine, I immediately started noticing a few issues post-swap.





Current Issues:


1. Lack of Torque:


• The 3RZ feels a bit underpowered in a heavy SUV like the KZJ71, especially during takeoff and uphill driving. I expected better low-end torque but it seems like the powerband isn’t matching the weight and gearing of the Prado.


2. Transmission Concerns:


• I kept the original automatic transmission (4-speed), and while shifting is smooth, I feel like it’s maxed out around 80 km/h. The RPMs are high, and it feels like the engine is pushing hard without actually gaining speed efficiently.


• There’s also a subtle whining noise that starts around highway speeds, making me worry about the long-term health of the transmission under the added stress.


3. Differential Ratio Mismatch:


• I suspect that my current differential gear ratio (likely 4.1 or 4.3) isn’t ideal for the 3RZ. I’m considering swapping to a 4.56 or 4.88 gear ratio to improve low-end performance and reduce strain on the engine at higher speeds.


4. Future Plans:


• I’ve been seriously thinking about installing a supercharger to boost low-end torque, but I’m concerned it may overstrain the stock automatic transmission unless I upgrade or reinforce it first.


• Also looking into installing a proper transmission cooler and possibly reprogramming the ECU or going with a piggyback tuner for better performance tuning.





What I Need Help With:


• Has anyone here successfully run a 3RZ with a stock Prado auto transmission long-term?


• What diff ratios are you using that balance highway comfort with off-road torque?


• Has anyone supercharged their 3RZ and kept the auto trans? What were your experiences?


• Would you recommend changing the full differential assembly or just the ring and pinion gears (crown and pinion)?





Any advice, experiences, or recommendations would be greatly appreciated. I really want to get the best performance I can without destroying the drivetrain.





Thanks in advance

 

[rakan100]

Correction:


In my original post, I mentioned that my Prado came with a 1KZ-TE engine. That was incorrect.


The original engine was actually a 2L-T turbo diesel.


Just wanted to clarify for accuracy

 

[Eurasiaoverland]

The 3RZ-FE has good low speed torque delivery, for a petrol engine, but I'm not sure it would be more than a healthy 2L-T at low speed. Is it definitely the fuel injected -FE variant? I know there are also carburetted 3RZ-Fs in the Middle East which will have significantly less power.

Have you done any basic checks (e.g compression) and maintenance on the 3RZ?

Have you compared it to driving a 3RZ powered 4Runner or Tacoma with an auto?

You've already done major conversions making it left handed and swapping the engine; personally the slushbox auto would have been the first thing I threw out. For lower capacity engines they really rob a lot of power and blunt performance.

I think a manual transmission and 4.56 diffs would transform the vehicle, providing the 3RZ is in good health.

 

[AirheadNut]

Thanks for clarifying that you replaced a 2L-T, I was wondering how a 3RZ could ever provide better torque than a 1KZ! Like @Eurasiaoverland said the auto transmissions can rob a lot of power, I've heard that the A343f in the LJ7x could take as much as 13hp just for the torque converter.

Have you confirmed that you still have torque converter lockup in 3rd and 4th gear? It isn't uncommon for the lockup solenoid in the valve body to fail after 25-30 years and the transmission looses lockup, causing the engine to rev a lot higher and the torque converter to suck a lot of power at highway speeds. Also, often times the torque converter is different for gas engines vs. diesel engines even for the same transmission, so it might be worth looking into seeing if the torque converter from a 3RZ spec A343f has a different stall speed than the one for a 2L-T.

The LJ7x series used 4.88 differential ratios, if you could source a set of 4.30 diffs from a KZJ7x or even get 4.10 ring and pinion sets that would probably help your highway performance quite a lot.

The 3RZ makes the same torque and quite a bit more power than a 2L-TE, so it should be perfectly adequate in a relatively "light" SWB Prado, but since it makes maximum torque at 4000rpm it will not feel anything like a diesel to drive. The 90-series Prado used the 3RZ-FE, likely coupled with the A343f transmission, so it isn't out of the question to put that combo in a 70-series Prado.

 

[rakan100]

Yes, it’s the fuel-injected 3RZ-FE — from a regular Hilux (not a Surf, those aren’t available here in Saudi Arabia).


Haven’t done a compression test yet, but that’s definitely on my list now — thanks for pointing it out!


The car originally had a 2L-T diesel with an auto, and I kept the same auto box after the swap.


I haven’t had the chance to drive a 3RZ 4Runner or Tacoma with auto, but I can feel the transmission holding the engine back, especially at low speeds.


A manual swap with 4.56 diffs sounds like a real game changer — really appreciate your insight

 

[rakan100]

Thanks for clarifying that you replaced a 2L-T, I was wondering how a 3RZ could ever provide better torque than a 1KZ! Like @Eurasiaoverland said the auto transmissions can rob a lot of power, I've heard that the A343f in the LJ7x could take as much as 13hp just for the torque converter.

Have you confirmed that you still have torque converter lockup in 3rd and 4th gear? It isn't uncommon for the lockup solenoid in the valve body to fail after 25-30 years and the transmission looses lockup, causing the engine to rev a lot higher and the torque converter to suck a lot of power at highway speeds. Also, often times the torque converter is different for gas engines vs. diesel engines even for the same transmission, so it might be worth looking into seeing if the torque converter from a 3RZ spec A343f has a different stall speed than the one for a 2L-T.

The LJ7x series used 4.88 differential ratios, if you could source a set of 4.30 diffs from a KZJ7x or even get 4.10 ring and pinion sets that would probably help your highway performance quite a lot.

The 3RZ makes the same torque and quite a bit more power than a 2L-TE, so it should be perfectly adequate in a relatively "light" SWB Prado, but since it makes maximum torque at 4000rpm it will not feel anything like a diesel to drive. The 90-series Prado used the 3RZ-FE, likely coupled with the A343f transmission, so it isn't out of the question to put that combo in a 70-series Prado.

Thanks for the great suggestions!


I swapped to the 3RZ-FE because I saw it in the 90-series Prado, thinking it would be a good fit. However, the performance isn’t as expected — it’s not bad, but something feels off. The swap was done professionally, but I suspect the transmission or torque converter might be holding it back.
To answer your questions:
1. Torque Converter Lockup: I haven’t checked it yet, but I’ve noticed the RPMs seem higher than expected. I’ll check the solenoid and make sure it’s functioning properly.

2. Torque Converter Differences: I wasn’t aware of the differences between diesel and petrol converters — I’ll definitely look into that.
3. Differential Ratios: I’m not sure about the exact ratio of my diffs yet, but I know they were originally 4.88 with the 2L-T. I’ll need to confirm the current ratio, but I’m considering swapping to 4.30 or 4.10 for better performance.
4. Power Delivery: I agree, the 3RZ is strong but feels very different from the 2L-T, especially with the torque coming in higher RPMs.


Thanks again for all your help — I’ll check these things and keep working on improving the setup

 

[rakan100]

Now my car in paint shop so I can’t drive it right now

View attachment 3883266

 

[Combat Wombat]

Ive driven a 3RZ 90 series prado with auto (here in Australia)
I honestly was surprised how well it went. If it wasnt for the colour of the vehicle I would have bought it!
The gear shift pattern and torque converter are definitely different between the petrol and diesel variants of the A343.

Also, the 3RZ is actually a sought after engine for turbo addition, but with an auto box it may be too much.

 

[rakan100]

Ive driven a 3RZ 90 series prado with auto (here in Australia)
I honestly was surprised how well it went. If it wasnt for the colour of the vehicle I would have bought it!
The gear shift pattern and torque converter are definitely different between the petrol and diesel variants of the A343.

Also, the 3RZ is actually a sought after engine for turbo addition, but with an auto box it may be too much.

That’s really interesting to hear — thanks for sharing your experience!

Honestly, seeing the 90-series Prado with the 3RZ and auto is what gave me the idea in the first place. The swap in my 70-series was done very cleanly, but the performance feels noticeably less than what I expected, especially compared to how people describe it in other platforms.
Your comment about the torque converter and shift pattern differences between petrol and diesel versions of the A343 really caught my attention. Do you know if the torque converter from a petrol A343 can be swapped into a diesel A343 case without major modification? Or are the valve bodies different as well?
Also, since you’ve driven one — did it feel responsive in the low end? I’m wondering if my setup is just suffering from a mismatch between engine and trans tuning.

Really appreciate your input — it’s helping me narrow things down

 

[Combat Wombat]

I would say that the low end torque was definitely adequate.
Diesel vs Petrol valve-bodies (Highly likely they are different)
Torque convertor likely will bolt on. Spline count and input shaft diameter may be different (like in later 1HZ setups)
Solenoids are easy to replace, and are a source of common failure if exposed to extreme head and low maintenance.
The torque lock up solenoid is a very common issue, and easily a 30min job to fix (including new filters and gaskets)
The actual transmission in the A343f is normally controlled by the ECU (integrated into the diesel ECU) but sometimes is a hydraulic pressure only and is pressure driven shift signals, so no electronics (very old style... like A440F in the 60 Series style)
The ECU can have damage from the Electrolytic Capacitors leaking and dissolving copper tracks in the ECU. Ive repaired probably 10+ in the last 5 years as a side business. But now as I have no test vehicle I cant verify working operation anymore.

It would be interesting to see if the 3RZ ecu is running your diesel A343f... or if some wizardry has taken place!

Honestly I would look at a dual vvti 1GRFE with matching auto transmission If you ever take the 3RZ out... (unless you plan on turbo add-on to the 3rz, it really is a commercial vehicle engine designed for reliability and efficiency instead of power)

Or simply source a complete petrol a343f transmission, and matching diffs and swap it all in!

 

[rakan100]

I would say that the low end torque was definitely adequate.
Diesel vs Petrol valve-bodies (Highly likely they are different)
Torque convertor likely will bolt on. Spline count and input shaft diameter may be different (like in later 1HZ setups)
Solenoids are easy to replace, and are a source of common failure if exposed to extreme head and low maintenance.
The torque lock up solenoid is a very common issue, and easily a 30min job to fix (including new filters and gaskets)
The actual transmission in the A343f is normally controlled by the ECU (integrated into the diesel ECU) but sometimes is a hydraulic pressure only and is pressure driven shift signals, so no electronics (very old style... like A440F in the 60 Series style)
The ECU can have damage from the Electrolytic Capacitors leaking and dissolving copper tracks in the ECU. Ive repaired probably 10+ in the last 5 years as a side business. But now as I have no test vehicle I cant verify working operation anymore.

It would be interesting to see if the 3RZ ecu is running your diesel A343f... or if some wizardry has taken place!

Honestly I would look at a dual vvti 1GRFE with matching auto transmission If you ever take the 3RZ out... (unless you plan on turbo add-on to the 3rz, it really is a commercial vehicle engine designed for reliability and efficiency instead of power)

Or simply source a complete petrol a343f transmission, and matching diffs and swap it all in!

Thanks a lot for your detailed reply! Really appreciate you taking the time.


To answer your question — I’m using the original diesel A343F gearbox (from the 2L-T setup) with the 3RZ ECU, and surprisingly, it works fine without any standalone controller. Not sure how, but shifts are smooth and lock-up engages properly.


Torque does feel noticeably weaker than the old 2L-T, especially on inclines, but it’s manageable on regular roads.


Everything’s actually working well — the reason I wrote the post is because when I hit around 80 km/h, it feels like I’m doing 140. The engine sounds like it’s maxed out, and the car feels like it’s pushing its limit.





Your suggestion about the 1GR-FE with its proper auto transmission sounds great — definitely something I’ll consider for a future swap

 

[Eurasiaoverland]

I can't add much, maybe just a reference point, but I can say that a 1996 Hilux Surf with a freshly rebuilt 3RZ-FE, 4.556 diffs and the 5-speed W59 transmission is a very nice vehicle to drive. At 140 km/h the engine is quite happy at something like 3500-4000 rpm, though this is definitely not my normal driving speed. I've driven it across Europe quite a few times and it'll sit at 100 km/h on most autobahn hills (except the big alpine passes) and get pretty much 10km/litre, even with crappy European petrol. So I think your auto is really holding it back.

 

[rakan100]

I can't add much, maybe just a reference point, but I can say that a 1996 Hilux Surf with a freshly rebuilt 3RZ-FE, 4.556 diffs and the 5-speed W59 transmission is a very nice vehicle to drive. At 140 km/h the engine is quite happy at something like 3500-4000 rpm, though this is definitely not my normal driving speed. I've driven it across Europe quite a few times and it'll sit at 100 km/h on most autobahn hills (except the big alpine passes) and get pretty much 10km/litre, even with crappy European petrol. So I think your auto is really holding it back.

Thanks again — that’s a really helpful reference!
Your Hilux Surf setup sounds ideal, and those RPM numbers at 140 km/h are way better than what I’m seeing. I don’t have a tachometer connected right now, but at 80 km/h, the engine already feels maxed out — loud and strained — so I’m pretty sure the auto gearing is the bottleneck here.
Appreciate you sharing your experience — it gives me a solid direction for what to aim for in the future

 

[Combat Wombat]

I also had a few Surfs/4runners over the years. I would still be driving one except being 190cm it wasnt the greatest ergonomics on long hauls (2300km across Australia, each way)
Number One was a white 4runner (Ln130) with the 2.8lt '3L' diesel 4cyl. had a 5 speed manual and on 31" tires it was a struggle at 100km/h
Number Two was a white RV6 4Runner with the 3.0lt '3vzfe' V6 petrol, auto. Could do 150km/h on 31"
Number Three was a beauty... Green KZN130 Surf SSR-X with 1KZTE and auto. Highly modified (rednek edition) Had to sell up and miss it dearly.

It would be interesting if you could source the correct matching trans and diffs for your 3RZ, I think it would do an admirable job once set up.
Especially once the turbo is installed!
There are some seriously decent valve body upgrades etc that can improve your trans. from a few suppliers (Wholesale Automatics in Australia make a few products)

 

[rakan100]

I also had a few Surfs/4runners over the years. I would still be driving one except being 190cm it wasnt the greatest ergonomics on long hauls (2300km across Australia, each way)
Number One was a white 4runner (Ln130) with the 2.8lt '3L' diesel 4cyl. had a 5 speed manual and on 31" tires it was a struggle at 100km/h
Number Two was a white RV6 4Runner with the 3.0lt '3vzfe' V6 petrol, auto. Could do 150km/h on 31"
Number Three was a beauty... Green KZN130 Surf SSR-X with 1KZTE and auto. Highly modified (rednek edition) Had to sell up and miss it dearly.

It would be interesting if you could source the correct matching trans and diffs for your 3RZ, I think it would do an admirable job once set up.
Especially once the turbo is installed!
There are some seriously decent valve body upgrades etc that can improve your trans. from a few suppliers (Wholesale Automatics in Australia make a few products)

Here in Saudi Arabia, it’s extremely rare to find a 3RZ paired with an automatic transmission from factory. The only common option we have is the KZJ90 Prado with the 5VZ-FE V6 and automatic gearbox.
I’ve been wondering if its transmission could be adapted to work with the 3RZ, but from what I’ve gathered, it seems to require its own dedicated transmission ECU.
Thanks again for the great info