20hp? that is a tad low I think. More Like 20-30hp for the cats and exhaust alone, and another 20hp for the pulley depending on what you are having done. As for the remap I'm not sure, I've heard that they do nothing and that you cant remap this engine? but i'm not a fan of remaps anyway. Read the sticky on K&Ns, you might change your mind on fitting one

 

There is no way the mods are a mere 20 odd HP - the performance is completely transformed.