The Magnuson-Moss Warranty Act basically says that a warranty can not be denied simply because the item has been modified - it must be proven that the modification caused the failure. I'd like to see someone prove that you blew your engine because you installed a set of lowering springs, or that your A/C failed because of it. Those are things Magnuson-Moss was designed to counter.

Installing a turbocharger on a factory N/A car, however, could easily void your warranty, but only for engine coverage. It would be tough to prove that the turbocharger was the fault of your seat heaters failing.

Some dealers are very understanding of this, others not so much. Some dealers will work on modified cars, others refuse to.