Just got a magnum rt
 

What Can i do to increase HP, i'm trying to get close to 400 HP!

How about a cam swap??

https://www.modernhemi.com/forums/internal-engine-5/comp-cam-install-5-7-hemi-491-hp-217/

:drive:

Nice gains. If I were doing it, I'd go with the 260. Reason being the torque would really help the big heavy car move off the line. My convertible is a ~3900 lb sled, and I prefer torque over horsepower in it. It doesn't hit 5500+ very often anyway.