98sr20ve

I dyno’d my car about a month ago with a test pipe and with the stock cat. I lost 15 whp at 5000rpm with the stock cat vs the test pipe but about the same peak hp. I did about 15 runs with the test pipe and then put the cat on and did 2 pulls. I don’t know why I would lose so much HP with the cat in place especially at 5K rpm. Does a cat need to be super hot to be efficient. Would only 2 pulls be enough to warm up the cat? Would a High Flow cat be any better? Here is a picture of my dyno. One pull is with the sr20ve cams and it nets 180whp, the other is with the sr16 cams and it nets 185whp the third is the sr16cams but with the cat and it losses about 15whp at 5k. Any ideas? I need to quiet my car back down so a cat or a new resonator is going back in its place.

__________________
92 240SX Project Car.