This article is from the VW Performance FAQ, by with numerous contributions by Jan Vandenbrande others.
A:It depends on what and how extensive you modify your car
and whether the parts are street legal. It also depends
on what country/province/state you live in. In the USA,
car warrantees are not automatically voided if you use
street legal (i.e., approved by the applicable
authorities such as the EPA/CARB/NHTSA) components. For
example, changing to Bilstein shocks will not void your
warrantee and neither will changing your muffler to a
Leistritz or Gillette muffler. Things become a bit more
difficult with engine modifications.Your warranty is not
voided unless the dealer can prove that your modification
caused whatever damage your car has. However, it may be
extremely difficult to convince them to do so, and more
than likely they will not want to help you.
 
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