Do they have a timing belt/chain that needs replacing every 100K like VW TDI's?
Just curious what's ballpark on making them run "correctly"? Anymore room inside over your MK4?
They use a chain and no they don't require replacement every 100k like a VW. I'll have to see what the recommended interval is, but my research hasn't found it to be an issue in the M57 engine.
This would be a Stage 2.5 tune setup:
Replacement intercooler to turbo boost pipe (factory is known to leak over time) $129
Remove exhaust, cut open and gut SCR, weld back shut. $0
DPF delete downpipe $600 (there is a cheaper version for $450)
EGR full delete pipe $225
Swirl flap delete $40
JR stage 2.5 tune $999
intake manifold gaskets $30
Vacuum hoses $25
Port wastegate on secondary turbo $0
Total of $2048
This would net you 345 hp and 544 torque to the wheels.
Stage 2.8 includes a different tune (+$300) and an bigger intercooler (+$600) for 379 hp and 595 torque.
Factory fuel pump provides enough fuel for either option and a secondary filter down to 2 micron can be added for ~$150.
Quite a few guys run a water/meth kit as well to help clean out the cylinder and around the valves due to the EGR sludge build up (coming from prior to the EGR delete).