The Bosch VE Injector comes with a guide pin and diaphragm that restrict the fuel delivery until there is sufficient air to burn the fuel. Replacing the guide pin increases the fuel delivery for the same boost pressure, thus improve your engine performance. That adds around 30hp and 50 lb-ft of torque, which is considerable for such a cheap and simple upgrade.
Remarkably this is actually supposed to improve fuel efficiency, so it’s really a no brainer.
Installation is the easiest of the upgrades, only requiring the removal of four screws on the top of the pump. This exposes the existing guide pin and the diaphragm.
The only trick is to ensure the new pin is facing the right direction. The stock pin is cone shaped so it doesn’t matter how it’s orientated but the upgrade requires the cut out to face the front of the engine.
I found this article on Driveline an interesting read on the various upgrade options for the DAF’s engine.