Hi, N54 engine has plenty of modification options but there is not much to do for the 2008 E71, however, you can start by having:
1. VRSF charge pipe.
https://www.vr-speed.com/vrsf-charge...1-f12-f13.html
2. N54 JB4 gains of up to 100hp and 100tq to the wheels on a stock vehicle
https://burgertuning.com/collections...formance-tuner
3. A custom exhaust can release some restrictions, ZEN RAGE can do it for you, check them out --
https://zen-rage.com/products/bmw-e7...31337368256593
Goodluck..