I have a 2016 Mustang GT. I've added headers and a Borla exhaust. Also, I put in a cold air intake. I'm pulling 400 hp at the rear wheels. Other than adding a super charger, any ideas how I can improve my HP?

 

Nope, that's about it for basic bolt on mods.

Any more engine mods will cost outrageous amounts for not alot in return. Compared to forced induction that is.

 

You would have to start talking major upgrades like nitrous, turbo, superchargers to see a big improvement.

400 rear wheel is darn good there...

 

You didn't mention a tune. An E85 tune usually adds about 10-15hp. From their you can get a GT350 intake and Throttle body. Those mods should net you 440-445.