[cleanspeed1]

There are a few things that you can do to that VAG based IDI motor, and since you are in Europe it will be a lot easier.

Add a turbo if it is naturally aspirated; get all the pieces from a 740/760 turbodiesel. Diesels run on an excess of air, and the extra air introduced into the system will allow leaner air/fuel ratios during cruise ( improves mpg ), cooler exhaust gas temperatures ( better reliability ), and most importantly, torque ( so you don't have to drive "foot to the floor" all the time, once again lowering fuel consumption ). With the modern turbo technology that is out there, you can have a responsive, clean running diesel that will be easier to drive. Head porting, as good as it is, is not something you want to do in a maximum mpg application because if you enlarge the port too much or get the shape wrong it can lower the velocity of the air through the port at low to mid lift ranges, reducing throttle response and torque. If you want to learn how to port a head, get an old head to work so that it doesn't put your car out of comission. Then take your home ported head to a reputable cylinder head specialist to get it flow tested and get a valve job that boosts the flow numbers in the .100" to .400" valve lift range ( you have to see how you did: convert the inches to mm ). Since this is an interference style engine, I will not go into a cam change or anything like that; with the turbo and some careful pump tuning, the engine will improve. Make sure you add an intercooler too. Cooler and denser air = better mpg.

Your car seems to be in a good place right now, and I never thought I would say something like "don't mess with it", but the hot rodder in me will never let that happen. If you haven't already, change the lubricant in the transmission and rear differential over to synthetic.

Then there is water/alcohol injection, propane fumigation...............oh no, there I go again.