In addition to everything allowed in Sport Category like spark plugs, spark plug wires and grounding cables, Tuner Category allows you to replace your battery—even to a lightweight one—and relocate it if you want. Of course, this doesn't apply to electric or hybrid cars, because we're pretty sure that would get out of hand! You can also replace the alternator and install things like electric fans.

Read the full rules to see details on things like cables and making sure it's all done safe.