This is my reservation about power mapping any of these cars, for anything other than economy and a mild bit of extra low torque. If I had a 3.0TDI as opposed to my 2.0TDI I would be even more reluctant since it's a strong fine motor anyway. I think personally they should never be ragged like a petrol, it should not be necessary with diesels. A quick assertive blip to just over 2K is what I always use, rather than a slow acceleration build up. It sounds smoother that way too, less of a tractor and I'm sure it keeps it cleaner. These engines were mapped from stock very conservatively and often appear to have less low down torque than you would expect from a diesel; mainly because of environmental reasons and longevity of the not so tough turbos, clutch and DMFs. Nonetheless a bit of extra torque should not be the end of the world as long as they are not ragged, like a petrol. Inadequate low end torque in too high a gear can be just as damaging on the clutch/dmf too.
This is quite a common misconception people have about diesel engines, and even just engines in general. Just because diesel engines produce a lot of torque (and therefore power) lower down in the rev range where they are at their most efficient, does not make it mechanically easier
for the components to deal with. A lot of people see power and torque as two separate measuring values, and while that's true to a degree, you must remember that torque is an instantaneous value, whereas power is a function of torque, over a given unit of time (also known as work
An example tends to make this easer to visualise. Both of these engines are doing the same amount of work
Power = Torque * RPM / 5,252
Diesel engine - 200lb/ft @ 2,000rpm -> 88hp
Petrol engine - 100lb/ft @ 4,000rpm -> 88hp
Now in the above example, for each power stroke, the diesel engines connecting rod has to be pushed twice as hard
, in order to make up for the fact it is spinning at half the rate
. This means considerable extra stress on components that are feeling these larger surges
per stroke, which is why diesel engines have stronger rods, cranks, and main bearings than their petrol counterparts, as well as components like dual mass flywheels, which (aside from smoothing the delivery) protect the gearbox input shafts from breaking due to mechanical fatigue. You will find threads dotted about on various forums where people have done single mass flywheel conversions on their mapped diesels and destroyed the gearbox because of this.
When you mention about being ragged like a petrol, up to a point, it is actually easier on a diesel engine when driven hard to be at higher RPMs, due to the factors I mention above. A diesel engine will be producing a lot less torque above 3,000rpm than at 2,000rpm, but the fact it's rotating 50% quicker makes up for that deficit, and still results in a higher overall power output. A case in point is this dyno graph for a stage 1 BKD 140 (essentially a transverse mounted BRE, like we have) from Darkside:
Remembering that torque is an instantaneous measure of twisting force, we can see from this graph that the engine is under the most mechanical stress at a touch over 2,000rpm, at peak torque, when cylinder pressure is at it's highest. Considerably less stress is being put through the components at 4,000rpm as torque output is lower, but as it's rotation faster, is still still making more power (doing more work
). Anything above that, and we will start to see that due to the heavy rotating components of a diesel engine, coupled with the small turbine on our BRE engines that cannot keep producing target boost at high RPM without over-speeding, mean it falls out of it's efficiency zone and power starts to drop for engine safety.
Now there is an upper limit here where the increased rotational mass of the heavier internal components of a diesel engine starts to brings it's own stresses, but any of the more modern diesels in our B7 will happily accept being revved out to 4k rpm in each gear with no mechanical concerns. Certainly that will be far more forgiving and less wearing on the components than full throttle labouring from 1,400rpm - 2,200rpm which is what a lot of drivers do with their diesel engines as it's what feels most natural (surfing the wave of torque). You will find that style of driving is what is hardest on all engine and drivetrain components.
This is why @Sloppy_1
said you can map 3.0 TDI engines hard if you drive them like a petrol, as at high RPMs the internal components of the 3.0 TDI will be under much less stress, as the torque produced at the high end of the RPM range is far more manageable, and combined with the higher RPM means for a high power output.
I realise I've just written a large wall of text, I love mechanical engineering, apologies for getting carried away