Maillemann: You bring up some good points. People have been tuning their TDis for a long time and getting great results. They have been doing this while keeping their fuel economy stable.
However, the modding of a TDi can have some pretty bad consequences. There is a thread over on
www.tdiclub.com that was recently started, where the OP got a HORRIBLE oil analysis while using a good Elf oil over aa standard 10k oil change interval. Why? Many people are pointing to his mods to car as being the culprit. Modding the car changes what the engineers had in mind for the car. The balance is ruined. Problems can come up. Then there is the whole subject of emissions. Whether they get worse or stay the same is up for debate. I have not seen much done in this area.
On the other hand, the NEW 2008 TDi engine is constantly referred to as a "clean diesel." It DOES have great emissions. Again, I haven't seen final figures on it, but there is no doubt that it performs better than an old modified TDi. I mean, it will be sold in all 50 states, so that right there tells you that it is clean!
So, in the end, the 2008 definitely does outperform a modified TDi. It goes way beyond what tuners have been able to do with their older cars. I am not attacking engine modders, as they definitely have come up with some impressive results over the years. They just can't compare to paid engineers who design cars for a living. That is what I want to say in a nutshell.
I can't wait to see how the 2008 2.0 TDi Jetta turns out. Should be great!