you might need to do it to any engine you buy unless its already been done as your going for 300+ bhp 
I don't no what to do yet because I could just map it to 300bhp on stock engine.
If I want 400bhp its roughly £1000 to rebuild it myself
If I want 500bhp it would cost about £3000.
I don't want to spend any more money on this car because I want to start my next project