400 HP out of your 3.8 would require more than forced air induction. Cam, valve train, fuel injectors, fuel pump, intake, exhaust, custom tune, just to name a few. And that doesn't get into everything you would have to beef up to handle that HP, like the transmission. My Trans Am with a 5.7 LSX engine runs over 575 HP, I have well over $15K into it (not including the cost of the car), and I still need a carbon fibre drive shaft and a stronger rear end to handle the HP. That engine started at 320 HP and is designed to be modded.
2001 Bonneville SSEi (retired at 365,000 Kms.)
2014 Jeep Grand Cherokee Overland (yes, I know its not a GM)