Golf TDI Chipping - bikemade3
What is the best way to go about getting say an extra 25BHPout of my MK5 1.9 105BHP Golf. These 1.9 TDI engines have come in many disguises ranging from 90 to 150 BHP so how did VW achieve these different power outputs.

Don't want to go mad with the power but the exra Tq would make the car a better drive and the MPG might improve.
Golf TDI Chipping - craig-pd130
The variant you have is based on an ancient VW engine block but with the PD "pump injector" system.

They only came in 105, 115, 130 and 150bhp variants. If memory serves the 105, 115 and 130 are very similar -- maybe slight differences in turbocharger and injector.

Lots of remapping & tuning box options, starting from about £200 to £500. You just need to decide if you want a removable external module (that you can resell later or if you change cars) or an ECU remap which stays with the car. Reputable companies include Superchips' Bluefin, Revo, Jabba Sport, Upsolute, Tunit (Bromleys), van Aaken, East Coast. All will give you an extra 25+ bhp and more importantly, extra torque.