I've had a 56 3dr TDI 140 for a while now, but have recently needed a 5dr car so bought a 2006 TDI 170 Sportback. Here's my quick comparison summary and thoughts so far! One thing I noticed straight away is how much quieter and smoother 170 engine is, it really is much better for refinement than the 140 (have driven lots of 140s and they are always on the noisy side of acceptable, especially when cold). The new CR 140/170 engines must be quite refined now. TDI 140 Positives - Great spread of power from idle (no lag) - Quick enough for most situations - Supreme economy (55-60mpg on motorway runs) TDI 140 Negatives - Noisier than the 170 with a gruffer note under power 170 Positives - Smoother and quieter than the 140 (still no BMW TD though) - Quick (not massively faster than the 140 though) but pulls higher revs much smoother and eagerly - No smoke due to DPF 170 Negatives - Horrendous fuel economy in urban situations (mid 30s) compared to the 140 which would still did mid high 40s. - Motorway economy is just about acceptable (got 49mpg in a strict 65/70mph 30miles round trip; the 140 would probably reach high 50s) - Slight power lag under 1800rpm, feels like it's laggy compared to the 140 but then suddenly picks up The mpg of the 170 worried me a bit when I picked it up and drove it home, steadily, at about 60-65mph, it was in that very windy weather we had a few weeks back and it only managed 39.5mpg with only short bit of urban driving either side of the motorway. The 140 would have done about 50mpg in the same journey I'm sure. I didn't read up about the 170 until AFTER I bought it of course! So I start reading about the poor mpg of the 170 engine and feeling like I've made a wrong decision buying the car as need the car to be economical due to work mileage. Also read about the DPF problems (regenerating and also a reason it has poor mpg) and read that removing it removes the problems, increases power (not bothered about this) but most enticing of all is a "10-15mpg" increase, which sounds like loads but also sounds like it brings it back to somewhere near the 140's mpg which sounds ideal.