All depends on your luck over 400bhp on stock internals and clearly how you drive. You could run over 400bhp on stock and be fine.. Many do but forging is the way to go. Rod job isn't advised on a 9 due to the difference in pins for the pistons. And dent will equal dead engine.
Wasnt aware of isue with a rod job on 9's?
Agree with everyone though, 400/400 is about right on standard internals, you can push it a little more without serious upgrades I wouldnt recommend.
On standard internals;
- Induction kit
- Full 3inch exhaust system (with decat)
- Fuel pump - most comon 450 Walbro
- 3 port solenoid to hold extra boost (although I would upgrade to an Electronic Boost Controller as they typically come with uprated solenoid and have more flexibility with map.
- remap
Think thats it
- You could upgrade the exhaust manifold to a decent aftermarket tubualr one but standard is fine for 400/400. Alternatively have it polished and ported for now
- An aftermarket turbo elbow may help too for extra air flow.
After that I'd look at clutch and flywheel upgrade before doing internals.
Handling mods go without saying to best get use of power too