Thread: Theoretical exercise RRC engine swap

I have been drooling over some of the om606 lr conversions on some of the uk forums, they fit in a defender so an rrc should be ok.
Auto would be ideal but i think you would have to use zf hp24 for it to last, from my little research the om606 is no easy to find in oz.


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For me sourcing a 606 is a doddle. It's pretty much the least of my concerns, however they are becoming increasingly sought after, so it makes them more and more expensive these days.
an OM603 would still be okay, but for that kind of swap I'd rather drop the v8 in.
Done the m117 into a Gwagen before so not worried, but since I'm an RR novice so to speak, I think the concerns for me are whether or not the ZF auto will last, whether the ratios are any good for a 5.6 v8, or if I should utilize the bulletproof 722.6 mercedes auto and programmable shifter.

Then I guess it would simply be easier to have bought a Gwagen instead, so perhaps just a 606 would do for the moment.

The BW transfer case is a concern because I do not know how much power it can handle or how good they actually are.

diffs / cv's I can live with until I learn some more about which are strongest and whether or not I swap out whole axle assemblies or just gut the internals.

I would like to do something about wheels & tyres down the track, so one of the key criteria for the swap will be if I can run a nice 33 or 35 MT or centipede etc and 'try' to keep it stock looking.

I would ditch the BW for an LT230 then there are no concerns, HP22 wont last long with 250 plus HP going thru it which is why i mention the HP24 even though it will need an after market controller.

If you look on LR4x4 there are a few OM conversions.

I think if I were to pursue the OM606 route, then I would be utilizing a 722.6 transmission, not the ZF. Mostly because I am extremely familiar with the 722 series MB transmissions (and they are pretty much unbreakable if fluid & filter service intervals are followed).
If I go with my spare m117 5.6, then the 722.323 that sat behind it would be utilized, - All MB transmissions can have the valve body modified (remove a couple of check balls and springs) to have manual lock out in gears and also the 1st gear start (most 722.3/4/5/6 transmissions start in 2nd gear for sedan applications)
the only major differences between the sedan transmissions and the Gwagen (w461/463) are the depth of the sump on the trans pan (identical bolt pattern, just deeper) and the manual gear lock modes.
Of course, using one of these means the transfer case must be divorced from the rear housing. I'm not entirely sure it's a good idea, but it does complicate things further, in terms of mounting etc. It does provide some alignment freedoms, but I have seen this become more of a problem than a boon in the past.
Another issue seen with the 5.6 swap, is torque loading.
In the 'G560' (was a 280GE) the amount of torque at idle loaded up the drivetrain in the G, so that holding the brakes and applying the tiniest amount of throttle, compressed the suspension by almost 4" of travel. Of course, G's have incredibly short diff ratios, and this was the primary cause. Burnouts however, in 1st, 2nd and 3rd gear were just a matter of applying a decent amount of wellie.
1st gear was deemed too short for anything but quite serious offroading, and low range outstanding. The vehicle really needed a set of 35" tyres, but it wasn't mine... so it remains to be seen how the owner contends with the short final drive issue.

I like the idea of the viscous coupling, but understand the issues it comes with, but it's nice to have fulltime 4wd. an LT would obviously change that.
I have fitted quaife ATB centres to my MB's before and would think that this would be an ideal alternative to an open centre transfer case, but again, I do not know the strength of the LR parts, or what needs to be done to achieve that 'bulletproof' reliability.

The main issue I have with contemplating the swaps, is simply turning the vehicle into a bastardized unit. I see many conversions, LS's Cummins, duratechs etc... they all have their advantages, but they also come with a number of penalties that owners either persevere with or become frustrated with.

So while I simply have a single issue with the 3.9 in that it is a gutless wonder and drinks like a sailor, I can live with it, as it is simply a fuel consumption issue.
Mind you, I never had the same feeling in my old GQ, or even the old 78 series utes I used to drive (loaded with 2 tonnes of equipment) - and yes, the tojo was the 4.2 diesel.....

So, will the 606 be worth it? possibly. certainly has the torque and power spread to make the RRC get up and really boogie, with the added reliability of the inline 6 mercedes donk. But I do wonder...... is a diesel conversion actually worth it, when outlay versus consumption over say... a 5 year period of ownership is concerned.

To give you an idea of consumption..... I'm currently hovering around the 20L/100km without trailer attached and about 26-28 with. I do mostly highway work, and find that 4th gear is a waste of time with the trailer, except on flat pavement. It's actually not much different without the trailer in that respect, and I would opine that the 3.9 wouldn't pull the skin off a rice pudding when really trying to get it moving from 90km/h upwards. That includes kickdown etc. it just revs and doesn't accelerate, especially uphill where it even loses momentum under kickdown - especially at around 90-100km/h. If this is normal for an RRC, then fine, but I would expect some form of acceleration with the kickdown from 4th to 3rd (and sometimes 2nd?) when the momentum drops like a stone.

So yes, I think a 606 or 117 would be an instant cure for that. however, in my old lwb 560SEL the fuel consumption was around 14/100 and if driven really hard, about 17/100. In the SL, the consumption is between 17-22/100 because I drive it very differently (and it is a lighter car than the w126)
interesting to note though.... in both of those cars, the transmission ratios are identical as is the final drive (2.47:1 - tall) and yet it is exceptionally well balanced between outright acceleration and cruising efficiency - something the Gwagen never was (arguably still can't - look at the 6.3 consumption figures these days) designed for anyway.

and the 2.02tonne RRC is right there with the w126 - while the 126 is a bit lighter, It's not about the weight. it's about the torque that the m117 v8 provides so low in the rpm band. and with the redline of 6500 (and believe me it will get there very quickly and easily) the spread of power is good. downside? fuel consumption.... it would probably end up being around the same 20L/100 as the 3.9 - but perhaps more importantly, the torque would be much better and the acceleration would make the car more driveable.

So yes, it's still theoretical still. But perhaps there are other engines which are cheap, reliable and have maybe 'better' fuel consumption and good torque figures, and are more suited to swaps...

And I still haven't contemplated the idea of different transmissions.... I'd like it to stay automatic, but certainly wouldn't rule out a manual..... it's simply going to depend on what is easiest to mate to the donor engine.

I think we'd all love a 7 speed semi-auto and a double low range, but i can't forsee that as being a viable proposition... I'd have to find some portals and a set of 35's to make something like that work..... and then how useful would the car be as a tow vehicle? hmmm

Originally Posted by Mercguy

To give you an idea of consumption..... I'm currently hovering around the 20L/100km without trailer attached and about 26-28 with. I do mostly highway work, and find that 4th gear is a waste of time with the trailer, except on flat pavement. It's actually not much different without the trailer in that respect, and I would opine that the 3.9 wouldn't pull the skin off a rice pudding when really trying to get it moving from 90km/h upwards. That includes kickdown etc. it just revs and doesn't accelerate, especially uphill where it even loses momentum under kickdown - especially at around 90-100km/h. If this is normal for an RRC, then fine, but I would expect some form of acceleration with the kickdown from 4th to 3rd (and sometimes 2nd?) when the momentum drops like a stone.

If you're getting that sort of power/economy out of a 3.9, there's something seriously amiss. The air flow meter has been known to cause similar symptoms.

Originally Posted by Scouse

If you're getting that sort of power/economy out of a 3.9, there's something seriously amiss. The air flow meter has been known to cause similar symptoms.

The AFM is clean as a whistle and working fine. there's no nasty purging of unburnt fuel or smell of rich running, Afaik, it was chipped according to Wade/Stuart. It's been serviced at Graeme Cooper's for the last 11 years prior to my purchasing - just over a month ago. It has no idle issues.

I live in a hilly area on the south coast, not far from Baz (or you actually) and the 20/100 is what I was told to expect by other forum members, and I can live with that. Towing the boat down from Qld netted me around 28/100. I expected something in the vicinity. This model has no O2 sensors fwiw.

The reason for the contemplation of the swap is primarily to reduce the consumption and increase the torque / power output.

the M117 v8 is good for 220kW and about 410Nm and a fuel economy of between 17-22L/100 when being pounded hard. in the 2.6tonne Gwagen it gets 20-22 with the short final drives, so I expect a fraction better if I were to swap into an RRC. However, the OM606 will provide more torque and lower in the RPM range, and the 5 speed auto works well with programmable shift. The issue with an MB engine swap is the transfer case being divorced from the transmission, thus creating extra annoying issues. And if push came to shove, then I'd probably ditch the BW and go for a VG150 from a w463. All in all, by the time that was done, I'd probably have been able to buy a 460.... Conversions are never cheap things to undertake.

I do have an opcon MX422 twinscrew supercharger here, but somehow I do not think a 3.9 engine would take 10psi of boost without heavy modifications.

would provide the extra torque though....

The only time I've ever come close to 20l/100km is towing a loaded car trailer.
Normally it was around 14-15l/100km from my 3.9 RRC & never a complaint about performance - I reckon it'd leave our 4.6 P38 for dead.

Originally Posted by Mercguy

I like the idea of the viscous coupling, but understand the issues it comes with, but it's nice to have fulltime 4wd. an LT would obviously change that.

LT230 transfer cases are still fulltime 4wd. Just with a manually lockable centre diff, rather than a viscous coupling.