Better question is, how many mods are actually tested on a dyno? I tire of guys saying they picked up Xhp from a mod, or even it feels like Xhp. Put it on a dyno before and after, that is the best way to tell if there is any hp increase. The next best thing (and more fun and cheaper) is to run it at a 1/4 mile track. Only problem with the track is weather conditions can affect results. But it is still better than, I put in a new X and I can definitely feel the increase in HP. You put the money into it and you want it to perform, so it does. The proof is in the puddin.
B-loose