The powertrain portion of the warranty goes "poof" the instant you do this, as does the emission system warranty. Folks who find warranty coverage to be of prime importance need to leave the internals of their engines alone. The only internal mods that don't instantly void the warranty are those street legal kits sold by H-D, like the 103 or 110 street legal kits for the TC96 engines.
Jerry
Not necessarily Jerry. It depends on the dealership. The Magnusson Moss Warranty Act basically says that the failure has to be directly related in order for them to void the warranty. If a dealership is following the letter of intent in the warranty act, then they have to be able to show that the modification was/is the reason for the failure. I've had a number of motor (stator, cam chain tensioners, etc.) issues taken care of on warranty without the mods to the motor ever becoming an issue.....not even a discussion about it. They even replaced my tranny mainshaft under extended warranty on a bike that had 66k miles and I was third owner pulling a Bushtec.
Simple engine mods (cams, A/C, tuner, exhaust) just don't seem to be much of an issue with the dealerships here in Nor Cal. You start boring, doing head work to the max, bumping compression way up, etc. that's when it starts becoming an issue out here.
