I think inspite of quoted vs actual fuel figures our diesels are delivering economy results that petrol owners can only dream about and the best aspect is we haven't had to compromise performance to acheive it. My E53d delivers around the 7.5l/100 highway if I maintain the 100-110 kph even with 10'' fr & 11'' re wheels, I know the remap decreased the fuel consumption probably by the amount the bigger wheels added, so it remains as it was. The exhaust system that BMW fitted to the 3.0d is very restrictive and as a result creates back pressure on the turbo, once I modified my mufflers the engine ran much freer and had more power. POWERS1 on the general forum has just modified his the same way, and posted me to say how much better it was. I've had a brief look at an E70 3.0d exhaust and it also looks very restrictive at the muffler not sure on the 40d.