usually easier to grind the head diameter a little smaller and then check it on a gram scale, your only gonna remove a tiny bit. The aaen pipes likely don't add much hp is what its showing you, if it doesn't pull weight then its not making a lot of power. The tach is like a dyno for say, if it over revs a lot its making more power and requires more weight to control the rpm. You also have to remember your wanting to turn higher then stock rpm also, so that will require less weight to do so. With the 15.6mm rollers it should take some weight to tame it down however the entire clutch set up has bearing on what happens as well, not all helix are cut on same radius, some are more aggressive upshifting, so youll end up with a little less weight depending on the cut and the finish angle.
