I have a funny story. Everyone always says on NA that test pipes don't give more HP. I dyno everything when I get a chance. I took my test pipe for testing the A/F ratio on my car with a wideband after changing cams in my car. I asked the dyno operator if I was going to be tempted to run the test pipe on the street. He said he had never seen a test pipe give much if any power. After tuning I put my cat back on and did another pull. HP was basically the same but I lost 15whp with the cat at 5k rpm. This is after both of my cams engage. I was shocked.