LT4 intake won't do much good without the heads to match.

 

With unported heads and am M6 you will be around 330 with a tune. Maybe your bottom end is balanced good from the factory and you pull out 340. Most M6 cars seem to be right around 330. Porting your heads will put you over 350, or even more. I have a buddy with an M6 with the Hot cam who puts out 380rwhp, 365rwtq.