General plan of attack is dp, full exhaust system, adjust the smic to catch better airflow, turbo (if possible) and either stage 2 or 3 custom code remap. Im looking for about 130bhp ish. im not chasing numbers but this sort of output suould bring a smile to the face in a car that weighs about 985kg!
Range information. Six engine choices are available: 1.4 (75bhp), 1.6 FSI (115bhp) and 2.0 FSI (150bhp) petrol units and 1.9 TDI (90bhp),1.9 TDI (105bhp) and 2.0 TDI (140bhp) diesels. Five speed manual transmission is standard, and 1.6 and 2.0 FSI models have optional of six-speed automatic transmission.
The clean diesel features particulate filters and other devices for removing diesel soot and order from the exhaust, as well as a system for reducing emissions. The 2.0-liter TDI produces 140 horsepower and whopping 236 pounds-feet of torque. While the 1.9-liter engine can best be described as peppy, the 2.0-liter TDI is down right quick.

I am less than convinced of the long term durability of a fuel pump lubricated in fuel (the PD pumps are oil lubricated) which develops pressures approaching 2 kBar. I went from a 2.0 TDI PD 140 to the CR TDI 143, as you say there is less 'percieved' shove but this is just because the engine is much more flexible - amazingly so.

I would sell the 1.8t car and buy a tdi or at least a tdi donor car. Unless you have the injectors, turbo, fuel pump amd maybe a computer fir that 1.9 you have it's going to add up fast. For the work and effort I would want the swap in something cooler than a mkiv. Physically, yes, it's simple.getting the Tdi to run won't be.
a T3 off a 2.5 CHRY gasser (much larger T3 than the stock diesel unit) a T3 off a 2.3 Pug TD a TD04 off a 2.2 CHRY a K24 off a VW 2.0TD a K26 off an Audi quattro
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is 2.0 tdi better than 1.9 tdi