Hey guys here's my 4 litre turbo 6 from OZ. Current mods are:
Replaced the intake system that crosses over the motor with a Process West Race airbox straight off the turbo.
Replaced the tiny factory intercooler with a big Process West item plus mandrel bent alloy piping.
5 inch race cat.
Larger fuel injectors.
Cut off the rear muffler.
Kompact blow off valve.
Full LED lighting inside and out.
Sheetmetal overflow tank, breather can, coil cover, lots of work with the polishing mop.
Removed rear spoiler and replaced with a G6E Turbo rear lip.
19 inch Konig wheels.
Autometer gauges through out.
Currently making 460hp at the tyres (342kw) and which is around the theoretical limit of the turbocharger plus the valve springs have had it. It still managed a 12.2 with a 1.8 60 foot time with the car misfiring from half track due to terrible valve float. Once the springs are done I think it can squeeze out an 11.5. New ones going in shortly plus next year a larger turbo, bigger exhaust, twin wastegates and custom exhaust manifold.
Hope you like, cheers