Low drag mods
Tyres, tyres and don't forget the tyres................
My 1.2 TDI winter Continentals vs summer Bridgestones sees at least 6mpg delta. Bridgestones are the 1.2 TDI model specific low rolling resistance 145/80 x 14 tyres on magnesium (yes MAGNESIUM) 4.5 j rims, covered with smooth plastic trims. Totally boring to look at and with limited cornering grip - offset by good ride, low unsprung weight and great mpg.
The other thing to do of course is take off as much weight as possible. First empty the boot .......If you've got a rear bench seat, look to see if you can fit the 1.2 TDI honeycomb equivalent - I seem to remember there's something like a 30kg saving for functionally identical items.
Many other parts of the 1.2 TDI are lightweight, not just rear seat and road wheels. Most are however model unique and not interchangeable, such as forged light alloy front suspension parts, light alloy shock absorbers, light alloy rear brake assemblies, light alloy engine block etc etc.
CD issues.
Underbody is fully shrouded. Transverse underfloor 'spoiler' on my car, immediately to rear of engine bay, is often knocked adrift - tie wraps more effective than OEM pop plastic pins. Other item to note is that front and rear wheel arch sections are also model specific - narrower and deeper to reduce gaps to tyre edge, and hence turbulent airflow.
Ciao,
Erling