Hey, I'm rebuilding a '97 jetta tdi, and I would like to get some tips on mods I can do as I rebuild it which will give better mpg's. I'm already employing the driving techniques, but want to ensure optimum fuel economy.
Hey welcome. If it were me, I'd consider removing the DPF (if it has one) which is illegal here, but it apparently helps MPG. I'd also consider a re-map, as turbocharged cars can benefit with both economy and performance with a few electronic tweaks. As you're rebuilding, think about replacing the injectors, as these can get gunked up over time. Perhaps consider aero mods and switching to a narrower tyre with a lower rolling resistance. Just my thoughts.
I think 1997 was before DPFs. The OEM fuel system might also be biodiesel compatible. Be prepared to replace the fuel filter several times, including road side, if you use biodiesel. There is going to be a lot of gunk built up that it will clean out.
Grill block is a simple mod that helps with aero and warm up times. A belly pan would help with aero, but a front dam is easier to do with much of the benefit. Maybe vortex generators, but these require string testing to get right. Then perhaps flat hubcaps. Any other aerodynamic mods beyond that will involve more work and changes to the car's appearance.
In addition to narrower tires, ones with a larger diameter will also help by making the final drive ratio taller. A lighter wheel and tire set will also help. As for general weight reduction, it comes down to what you are willing to take out and off of the car.