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P38 2.5 dse turbo questions


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I'm struggling to find much info on the turbo setup on the 2.5 P38. Can anyone help me with the following

1. I've read that the car runs 1.2bar boost - is this correct cos its seems a lot? I thought diesels ran low pressure turbos but a higher compression stroke (sorry i have lots to learn about diesels)

2. Turbo make? - Mitsubishi TD04-11G4 - I've also seen Garrett listed or are these hybrids?

3. Actuator setup - are these sprung loaded? What determines the operating parameters of the wastegate?

4. Do tuning chips like the PSI box increase the boost pressure? Is this achieved from bleeding air away from the actuator if this is preset at 1.2bar? Or are the power gains purely from cleaned up fuel maps....which leads me to my next question...

5. I live over 1000m above sea level, and the oxygen levels are not "dramatically" different, but it is thinner...what would be the effects of fitting a Powerbox that has been remapped in different atmospheric conditions?



1997 2.5DSE

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Lifes too short to worry about RR BMW diesel performance. If it works leave it alone. ;)

Accept that nothing "extra" happens when you put your foot down apart from an increase in noise and fuel consumption.

If you are after performance fit a V8 (and find a whole new set of problems to discuss, with slipped liners and warped heads).

It's Friday, spend time/money on beer. :P

Sorry I'll stop it now. (3hrs 47mins 20s to the weekend)

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If life really is so short for you why bother to write a reply that contains absolutely zero information regarding the topic.

As it happens I am worrying about the cars performance, and trying to ascertain whether or not it's suffering from wastegate creep or something else. I live in the middle of Spain MILES from anything. My car has a tough life everyday - 4 months of the year it spends it pulling 2000 kgs up and down mountains tracks. This is what I need performance for - full power/full boost when requested to get me out of any sticky situations. You've got to have faith in the car and its abilities....I simply cannot do without my car, which inevitable means lots of maintenance. I bought a diesel because I thought it had more torque lower down the rev range and they're generally known as being more bullet proof than petrol engines. It's my first diesel, and like I said I have lots to learn, so unluckily for all you beer swilling speed freaks that's going to involve you answering some questions, no matter how stupid they may seem to you.

The V8 is simply not an option.



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Hi Matt,

I've not seen a comparison of torque curves for the diesel and V8 P38s, but I'd be very surprised if the diesel has more torque at any point than a V8 (4.0 or 4.6). Low down torque is one of the strengths of the V8, whereas the diesel is a considerably lower capacity engine with significant turbo lag. On the other hand, fuel consumption is not a strong point of the V8, which probably rules it out for you if you're using it in anger most days.

I've no idea of the technical stats for the diesel - if you can't find them for a Range Rover, try looking for BMW 5 series (what the engine was originally for) or Vauxhall Omega - the engine is a BMW M51, IIRC.

My impressions from running a P38 diesel for a year (well, 9 months - it spent most of the last 3 in a garage before I ended up selling it spares or repairs :( ) was that it went fairly well for what it was once the turbo had spun up, but the lag was horrendous (a friend who's father had a BMW with the same engine made the same observation). I'm fairly certain the commonly available performance upgrades are simply changes to the fuel maps, but most people who've had them done report much better torque from low revs and less lag (and often better fuel consumption, which they usually attribute to not having to cane it as much). I'm only repeating other peoples' views here though.

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Hi, Matt, beer swilling speed freak here, :)

Now you mention the reason you are after the torque low down and the power I can see why you were asking the questions to begin with, and respond. A little background info would have been useful to base my reply on. In my limited experience of the P38 BMW diesel engine and threads about it, it is best not to modify it much beyond a PSI box.

My brother has such a box on his, which was present at purchase. The only thing it does as far as I can make out it is modifies (increases) the amount of fuel by fooling the sensor above the fuel filter and another value into the engine ecu.

Inside the box is a pic 16c57 with a few external components (about £5 worth of bits in total). For £300 retail its a bit pricey.

The reason I said to leave it alone is the stories I have read of diesel owners chiping the engine and using the extra power all the time flat out, which leads to overheating of cooling system and egr turbo temps. Warped heads result. If you look after the cooling at the same time by way of a bigger intercooler and new radiator/electric fans, to keep the engine cool it should be o.k

Regular oil/filter changes as you say are a must.

From what I can make out the BMW engine is underpowered for towing/performance use. The main use for these engine was bmw 3/5 series and the vauxhaull omega, and to sit on a autobahn all day in cars which weigh a lot less than a p38. Search BMW M51 engine tuning. The follow on engine the M57 was a lot nicer, finding it's way into the newer 3/5 series and the RR 2002-2008?.

As Geoff says it takes a bit of winding up to get it to speed, once there the revs will drop back and it is relatively civilised.

Towing a caravan or trailer on country roads/inclines can be wearing with lots of revs and not a great deal of progress.

This is the reason people search out chips and tuning.

Based on your use for the RR I would say the engine is probably the weak link, I would personally have gone old school with a RR classic, disco or defender with a 300TDI minus ecu/egr for simplicity. If cash was more plentifull I would buy a disco 3 tdv6 tomorrow, they can tow 3.5 tonne without even knowing it is on the back. I run a 300tdi ex mil defender which has no problem towing anything but is really not for everyday/long journeys.

Hope this helps, a bit more than the original post.


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Thanks fellas, I'll trawl through the BMW archives for any other info I need specific to the M51. I'm sure you appreciate why i need to stay on top of maintenance and possible probs, and my goal ultimately is simply to make the engine run better. My thoughts are, that in an environment where oxygen levels are depleted I suffer from "over fuelling" (lack of power) more, especially when it's under load. When i'm off tarmac with the trailer i'm usually in Low ratio, so i have no problems, but it's another story once i'm back on tarmac. The inclines make it almost unbearable, but thankfully there generally short runs.

I have an old classic too, fitted with 300tdi and 4" lift. It's a totally different Rangie, the two cars are light years apart. The classic will pull 2tons easy and it's responsive when it does so. It's a great car and a true offroader....but it's old now, electrics are suffering (something i know very little about) body is not so good, gearbox is playing up, heater matrix died sometime ago so would need a fair bit of spare cash to bring it up to Spanish legal standards. I still prefer towing with the P38 as it's much more stable, and i like the auto box.

You're probably right, a disco or defender may well have been much more suitable, but sometimes my irresponsible side has it's way....i should really remove the air con system if i was serious about performance, but i can't bring myself to do it, so it remains switched off for 9 months of the year.

Thanks again


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