Has anyone ever lost power after getting a Y pipe? or maybe have gone to the track and ran worse then before they had it?

I went to the track last night, and ran a 15.31 with only a Stillen intake which is .5 seconds faster then the 15.87 that I ran stock. A buddy of mine has a 1996 SE 5spd with intake, UDP, Stillen Y pipe. He had troubles shifting and launching all night and ran 18 seconds a couple of times. He asked me to take it for him on one run and I ran a 15.695 with it. worse then what I was running with much less. Was there maybe something wrong with his car? I did not remove anything from mine, but he removed the back seat and spare/jack, ect.
Any ideas?

 

could he possibly have a knock sensor or any other type of codes on his ECU?

 

talk to emax