We are talking about the engine that brought a reliable diesel engine into the mainstream and is still highly regarded today. The legendary ALH (1999.5-2003) and some of these mods will also apply to the BEW engine as well.
Improved Airflow, clean your snow screen and swap out the intake manifold for either BRM or at least an intake from a European PD150 engine. Leave the airbox alone, it's fine for well above 200HP.
ECU Tuning, a proper ECU tune really brings these TDI's alive. Especially when you stack them with other mods. Go with a reliable and respectable tuner, don't waste your time with those plug and play "tuners" on ebay.
Nozzles, there are a few brands out there. We carry DAP nozzles manufactured in Italy. That's all we carry. They're solid and we trust them. Bosio are excellent too, if you're reading this you probably already know that though. Avoid red top nozzles on ebay, they're probably from china and you're better off setting your money on fire.
More to come.