if you got 10 hp to the wheels from the header by its self, you would never feel it. So dont be so quick to say it did nothing. Its for this reason that lots of people think a 4cyl isn't worth messing with. And why some many poeple do a v6 swap. you also have to take in to account were in the RPM range the power is. 10ph dosn't mean 10 at every RPM. it may only be at 4000 that its that much and it could be that at 3500 its only a 5ph gain.
