Welcome along. You be supprised to find out (maybe not) the 318 and the 320 are both 2l engines. 2005-2007 318d's 120 bhp 2007 onwards 318d's 141 bhp 2005-2007 320d's 161bhp 2007-2010 320d's 175 bhp Im not sure if they are actually the same engine, maybe the 318 detuned? But my advice is go for the 320d.. Tax is the same as a 1.6 petrol and your going to get the near performance of a 323 petrol!! My 2003 320d @ 150bhp, is only, I think 0.8 seconds slower to 60 than a 323 (2.5 litre) And still returns over 55mpg? I think you may be a little dissapointed with the 318, for pretty much the same price mate go for the 320d