I am going to attempt installing a 1.9 TDI diesel in a light truck, it will be my fall project. I have the truck and am now looking for the TDI engine. My question is this to any of you who may know. Has the TDI engine itself, not the fuel system or the turbo etc, but the basic engine block and head stayed the same thru the years? The reason I'm asking is because I wanted to know for example if i bought a late 90's model or early 2000 model engine would it be upgradable such as turbo's and other things of that nature where i could improve horsepower and efficiency if needed. The engine codes and variance in horsepower through the years is a bit confusing. Any help clearing this up before I buy would be greatly appreciated.