I went to the track and ran a 14.85 at 93.6 mph. The only change was adding the exhaust. Prior to the exhaust I ran a 15.10 at 92.3 mph. The weather was only about 15 degrees cooler and this calculates approximately to a 18 - 23 hp gain. Again, I am only approximated the gain from the change in mph, using the hp formula. But at least the exhaust didn't hurt the performance and with K&Ns, it may even do better.