What speakers stereo system etc do i need to make my car loud ?

Alright i replaced my old *** radio in my mazda with a newer pioneer stereo puttting out 50 watts x4 . it blew out my old speakrs so i bought some sonys spakers each 150 watts . I dont kno **** about this so please help me out. They are loud but not even close to wat im trying to get. My friends 2008 nissan altima is loud. u can hear it from a couple blocks. i only have two speakers right now and want to kno do i just buy more or do i need a stronger stereo or wat.