Not impossible - smooth driving has got me an average 60.7mpg over 80,000 miles, measured brim-to-brim with each fill (Mk2 2007 1.6TDCi). Dropped to mid 50s over the past few months but now better after taking out the dpf. Managed 65mpg on a 1,000 mile trip from Wales to the south of France last weekend, mainly 70mph motorway speeds with the odd slower section due to heavy traffic. I've got an egr blanking plate but not fitted it yet - might see a small further improvement after that.
On the turbo question, we seem to have a range of between 1000 and 1700prm for kick-in from the posts above - is there a definitive answer or does it depend on the engine model and the way its tuned? I used to notice a pick up in accelearation at about 1500rpm, but now it pulls nicely right through the whole range - is this due to the remap done at the same time as the dpf removal?
These turbolag/ power delivery/ boost threshold issues are complicated to explain
1st of all it may seem like the "turbo kicks in" at specific revs, it does not, it depends on factors like temprature, load etc
The turbo will boost completely differently in 1st than it does in top at the same engine revs as the transient or time response is different and the engine revs do not match the turbo revs
So in 1st, the engine can rev through its powerband quickly (due to the realatively light load) and the turbo can have difficulty boosting fast enough (more about transient response/ (time) than revs) so the turbo may lag behind the engine, in a higher gear, the turbo has more time to boost, as the engine revs through its power band slower, so the turbo has more time to "catch up" with the engine
So some turbo diesels accelerate faster in some gears than others (and not in the way expected)
The DPF forms a restriction on the output of the turos turbine, removing it allows the exhaust gasses to exit sooner, faster, that makes the turbine spool sooner, quicker, from lower revs, the turbine is connected directly to the compressor - so if the turbine spools quicker the compressor does too - the compressor spinning up quicker allows more boost, quicker, on demand
The same boost control systems are still in place so the peak boost is not increased but the throttle response is improved, and the engine should bull better from lower revs and stronger through the powerband
The remap should work in conjunction with the DPF delete to make an integrated system/ tune to increase power/ torque through the rev-range the additional energy from the extra fuel added increasing the energy in the turbo, in turn
Ive dumbed it down a bit because i don't really know how to explain things like the difference between the boost threshhold and "true" turbo lag