Blasting a fan onto a car that isnt actually moving isnt going to simulate how a filter functions... for example the myth about vipers producing better results by not connecting the feed, I have no doubt in my mind that a viper with the feed not connected will get better results on the rr than a properly fed viper from the wheel arch, but actualy on the road im sure the fed viper will function better and perform better. Also you could take your car in for a rr with filter "a" on then weeks/months later have filter "b" rr and get completely different results, some people will think this is due to the filter change... its just that rr's are not that accurate and for it to spot something that increases/decreases hp by 1/2hp is very hard.