If you're looking for TDI performance, you'll end up with the engine code letters AXG / AHY with the VTG turbocharger from the 150hp model.
The T4 catalogue provides everything for a conversion. Upgrade components such as stage 1 or stage 2 turbochargers, injection nozzles and exhaust systems are also available.

Especially with such an upgrades, the downpipe forms a bottle neck. The diameters chosen by VW are quite narrow. This problem was the typically tackled by highly talented do-it-yourselfers. Whoever could not do this was deterred by the high prices of wage-finished items.
 

Doris fully utilizes the available geometry. The diameters were increased by 20% compared to the series.
Doris does not have an ABE and is only available for motorsport or for show purposes.

Dagmar is a stainless steel stencil to cut exhaust gas recirculation seals. The AGR can also be closed with Dagmar
at short notice for test purposes.
Closing the EGR leads to a worsening of the exhaust gas behavior and is not permissible.

 Closing the EGR leads to a worsening of the exhaust gas behavior and is not permissible.