I have been doing a little reading...

My understanding is as follows...

Borg Warner produce a K03 Turbo that is fitted to our cars. (Polo GTi) There are a few different types of K03 Turbo. Apparently an older version, known as the K03 with 12 blades and a revised version with 8 blades and different actuator known in tuning circles as the K03S (but not its official name).

Apparently the K03S can hold a little more boost and flow a little more air.

My reading leads me to beleive the Polo Gti has the more efficient K03S.. but the Mk4 Golf Gti also with a 1.8T the older K03.

My further reading suggests this K03S turbo is good for around 215hp (160kw) without overspeeding the turbo.. The previous version K03 good for 195hp (146kw). APR on its site has different outputs for Polo Gti and Golf Mk4 chipped. (does this confirm the K03 vs K03S)

My reading also suggest that the K04 Turbo which is considered an upgrade for our cars is only good for 220hp without overspeeding the turbo. The K04 has 8 blades of slightly different design which can flow a bit more air.

If what I read is true, what is the point of spending $3000+ to change our K03S Turbo for the K04?