Rather than going for an expensive replacement turbo for the K04, such as the Garret one mentioned above you can have your exisiting K04 turbo modified.
This is relatively new for the K04 but some companies now offering this modification.
Secondly just out of curiousity you say have an 'FR'. As standard the FR ran the K03 turbo so assuming you already upgraded to K04? If you do still have the K03 then 300 bhp is probably about right as you looking at 40bhp difference as standard k03 v k04.
Might also be worth adding an intercooler such as one from THS or APR to keep things nice and cool and possible looking at a better induction kit that your CAI.
What remap are you running, revo, custom code, GIAC etc? You mention a stage 3 meth-map ?
hi how can i check if i have the K03 or the K04? also if i have the K03 is it just a simple swap over?
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Realistically though, without trying to sound negative about it, even if it was say 20bhp more, how much that would equate to on the road when you are near enough at 400bhp anyway?