Might be ridiculously stupid, BUT...

I am curious. Is it possible to get 500+ hp from the 420a motor?

Yes, but it would take a lot of money. They make engine build kits and turbo kits. I have actually seen few 400hp 420a avengers and they are sweet. It is nearly the same as an eclipse/talon and those have many aftermarket parts. The SRT-4 is a stroked 420a, 2.4L instead of 2.0L. Hahn racecraft makes turbo kits as well as exile racing or any kits for eclipses.

I'm gonna do it! Shiz! I've seen a honda civic hatchback smoke a viper! That's what I'm gonna do. Screw the viper. My car will be called the antivenom. BOO.......YAH.