4BD1T vs OM606

[GlacierRover]

Hey all, I have a 1994 200TDI Defender 110 that I've had for about 5 years now, and while the 200TDI is still chugging along I still find myself going through the hypothetical exercise on what I'll do if/when it decides to bite the dust. I don't mind the engine now, but even with an upgraded turbo and intercooler with a turned up injection pump it still leaves a little to be desired, especially in the mountains where I live. I love the simplicity of mechanical diesels and if I ever did decide to swap in a new engine I would want another diesel of this nature, and as of now I'm hung up on the Isuzu 4BD1T vs the Mercedes OM606. I'm still kind of early in the research process so I'm sure I'm missing things, but here is what I have compiled so far for what would be needed for each as well as a Pros/Cons list:

Mercedes OM606:

• Upgraded transmission (Want to stick with manual, Ashcroft HD R380 stumpy, BMW ZF 6 Speed?)
• Modified Oil Sump
• OM603 Mechanical Injection Pump
• Adapters for transmission to engine (possibly also transmission to transfer case)
• Engine/Transmission mounts
• Cooling package (radiator, intercooler, electric fans?)
• Other various ancillaries

Pros:

• More refined/less noise and vibration (torque spread out over 6 cylinders)
• Lighter
• Can part out donor car and make a decent amount of money back

Cons:

• OM606s are relatively rare in the US, getting popular for swaps and going up in value (low mileage cars $9-10k, beater cars with 250k plus miles are $5k)
• Possibly more expensive swap

Isuzu 4BD1T

• Upgraded transmission (Isuzu 5 speed)
• Adapter for transmission to transfer case
• Engine/Transmission mounts
• Cooling package (not sure what the Australian Perenties use?)
• Other various ancillaries

Pros:

• Potentially more durable/reliable (splitting hairs as OM606s have a pretty good track record too)
• More torque (potentially better off-road engine)
• Cheaper donor vehicle (Isuzu NPR truck that would have the needed engine and transmission can be had with relatively low miles for $5-7k)
• More authentically Australian with a Perentie vibe (my Defender was imported from Australia)
• Possibly cheaper overall swap

Cons:

• More noise/vibration (wondering how a 4BD1T would compare to a 200TDI?)
• Donor vehicle would likely have little of value to part out once the engine and transmission are removed
• Heavy

Any thoughts on comparisons between the two? Obviously the 4BD1T has the proven track record in the Australian Perenties and they seem to love them on the Australian forums, but I haven't seen a lot of feedback yet on completed OM606 swaps and how they have faired. What say NAS-ROW?

 

[expanse]

I'm bias AF with 606, but even with me doing all the work and fabrication, it's still not cheap. I've got zero seat time with the isuzu lump so can't speak to that.

Whats your use case for this build; commuter, weekend trail rig, overland long hauls?

 

[GlacierRover]

Mixture of weekend trail rig, drive it to work occasionally, and slowly building it up to be an overland long hauler. I used it as a camping platform for a week long hunt in the rockies and it did great. Curious how the 606 has performed for you with noise level? I'm not overly concerned as I find my 200tdi bearable, but was wondering how the 606 compared.

 

[UnfrozenCaveman]

I've had a normally aspirated 4BD1 in an '88 Perentie since 2017.

I live at ~900' of "elevation" so it's pretty adequate here in Iowa ... when I go west, it's a bit (okay ALOT) slow.

It's paired with an LT95A (tapered roller bearing mainshaft) that's allegedly pretty reliable but will fail at some point.

It does not like to be hurried shifting especially when it's cold.

Noisy? ... not a problem in town or earplugs on the road I've driven it to UT and back four times so far.

Matt Jackson ("bluebomberlr88" many places online) has a turbocharges 4BD1 mated to a modern 5-speed ... darned if I remember what he's used...and lives in central California. PM me for his contact info.

It gives 23-25mpg in town, on the highway and slightly more than that off-road...lot's of putt-putting, not much throttle.

I've never had any other diesel experience, so that that for what it's worth

Good Luck!

 

[GlacierRover]

Yeah if I went the Isuzu route I'd use the Isuzu NPR truck as my donor vehicle which is the turbocharged version, which I've read can produce an abundance of power. Hoping it can be mountain worthy with some tuning tweaks. Appreciate your insight!

 

[Grnrvrs]

I have a 4BD1T in my 110. I live at 7400 in SW CO, and am constantly up and down the hills. I don't expect to drive 80 up mountain passes, have been accused of driving like an grandpa, and am super happy with the 4BD1T's performance. The stock turbo stinks, lots of turbo upgrade options. I run a HE221W.

 

[steinhnj]

Yeah if I went the Isuzu route I'd use the Isuzu NPR truck as my donor vehicle which is the turbocharged version, which I've read can produce an abundance of power. Hoping it can be mountain worthy with some tuning tweaks. Appreciate your insight!

There are some differences in the 4BD1(T) from an NPR truck and a Perentie. Can’t remember off the top of my head, but there are differences. Would need to figure out what they are. KLR in AUS sells replacement parts for the Isuzu, and I’ve had good luck using the Perentie Parts manual available for free on line, to get Isuzu part numbers and then buy the parts here in the U.S. My Perentie has been my most reliable car for the past 8 years. Quick Draw (in the U.S) offers a Tremec transmission kit for the Perentie. Others have used an R380 with every HD option available, but when I emailed Ashcroft, they said they wouldn’t trust an R380 behind the Isuzu 4BD1T. Some say its the “torque pulses” that kill the transmissions behind the 4BD1. 3.9L displacement from only 4 cylinders. Isuzu used an MSA 5 transmission and it works out great. There’s some custom work required to get the MSA to work.

 

[GlacierRover]

There are some differences in the 4BD1(T) from an NPR truck and a Perentie. Can’t remember off the top of my head, but there are differences. Would need to figure out what they are. KLR in AUS sells replacement parts for the Isuzu, and I’ve had good luck using the Perentie Parts manual available for free on line, to get Isuzu part numbers and then buy the parts here in the U.S. My Perentie has been my most reliable car for the past 8 years. Quick Draw (in the U.S) offers a Tremec transmission kit for the Perentie. Others have used an R380 with every HD option available, but when I emailed Ashcroft, they said they wouldn’t trust an R380 behind the Isuzu 4BD1T. Some say its the “torque pulses” that kill the transmissions behind the 4BD1. 3.9L displacement from only 4 cylinders. Isuzu used an MSA 5 transmission and it works out great. There’s some custom work required to get the MSA to work.

I didn't know there were differences between the engine in the NPR trucks vs the perenties aside from the turbo, that's good to know. I'll have to see what the differences are to determine if that would cause problems for a swap. I was tracking the MSA transmission and I believe that is what is in the NPR trucks, which was what was appealing to me as I could get the needed engine and transmission from a single donor vehicle.

 

[Grnrvrs]

The Perentie version of the 4BD1T has an oil filter offset block, readily available at KLR. Some Aussie spec 4BD1 and 4BD1T's had a different oil pan with a larger sump, diff engine mounts, air filter assemblies... all easy enough to deal with. The real issue in going the MSA route IMO is the shift linkage for the transmission. There was a fellow on AULRO that had designed and built a couple linkage sets, not sure of the current status. Personally, I like the LT95A. While all gearboxes will wear out eventually, it is not a weak link.

 

[rocky]

I think Milner was the company that made the Isuzu to LR gearbox adapter. Suspect they are long gone out of business.

 

[GlacierRover]

I saw that a couple of outfits in Australia made the shifter linkages and transfer case adapter for the MSA gearbox, but I'm not sure how active they are now. If I decide to go this route hopefully I can dig something up, I figure KLR is a good place to start to track it down.

This has been awesome information so far, any thoughts on the Isuzu vs the Mercedes?

 

[lcdck]

I always thought the Isuzu power output was relatively low, similar to the LR tdi engines. Am I wrong about that? Maybe the turbo swap mentioned resolves that. The OM606 is a beast and can be tuned to more power than you could use. The Brits are way ahead of us on that swap so if you have a RHD truck (sounds like you do) the swap has been well sorted with a few options for vendors of parts. I’m not sure if the 4BD1(T) swap would be as easy to find all parts for.

 

[steinhnj]

I always thought the Isuzu power output was relatively low, similar to the LR tdi engines. Am I wrong about that? Maybe the turbo swap mentioned resolves that. The OM606 is a beast and can be tuned to more power than you could use. The Brits are way ahead of us on that swap so if you have a RHD truck (sounds like you do) the swap has been well sorted with a few options for vendors of parts. I’m not sure if the 4BD1(T) swap would be as easy to find all parts for.

I own both a turbo’d Perentie and a 5 door 300Tdi. The Isuzu is hands down more powerful. My 300 is tuned up also with new injectors, new turbo, and new IP. The Achilles heal of the Perentie is the 4-speed LT95A. Plenty of AUS guys have put an R380 behind the Isuzu and have good results. Just use 5th like overdrive, and don’t mash the skinny pedal in fifth gear. RoamerDrive in Canada was teasing an adapter plate for an NV5400 to Isuzu 4BD1, but don’t know if it ever materialized. My choices would be 1-QuickDraw package, 2-Reach out to RoamerDrive, 3-R380.

 

[rocky]

BTW there will be a few perenties up at Winter Romp including a FC101 with the Isuzu engine that my long time mechanic built.

 

[Grnrvrs]

If you can, definitely check out some the different vehicles/configurations.

While the LT95A (diff story than the LT95, the LT95A is the most reliable transmission LR ever built, IMO) is slow shifting, loud, and is a very old design, I love it.

 

[GlacierRover]

I was hoping to stick with the Isuzu MSA gearbox if I went the 4BD1 route given it comes with the NPR donor truck. Seems like a plenty strong box that was designed to run with this engine, but looking on the AULRO forums I'm a little concerned that the guy making the adapter plates for the transfer case and linkage adapters disappeared. I'll look further into the QuickDraw package and what RoamerDrive has going.

 

[turbodizzle]

I don't know anything about the Isuzu engines, but the Mercedes gets my vote. It has tons of aftermarket support and is capable of making more power than a Defender can use.

 

[saetaes]

I saw Mike from Britannica Restorations on YouTube has been doing a series on his 110's 4BD1T recently:

https://www.youtube.com/@BritannicaRestorations/videos

Might be interesting to follow.

 

[UnfrozenCaveman]

I can't believe he didn't know that little tube filter was in the bottom of the IP !

I clean mine every oil change, it doesn't catch much bit it's nice to think I'm keeping an eye on it.