I have them on a slightly? modified 87 with 3" basani h-pipe and exhaust all the back and it sounds great, as for as hp improvement I cant tell you all the mods were done at the same time so its impossible to judge. I do have to be carefull going into and out of driveways due to the headers ground clearance. The car did break 2 highly modified c-4s at the track using MT slicks before I switched over to a t-5.