One of the most common upgrade to free up the power from your ride is by changing to a free flow exhaust system and that doesn't mean you must use those $600-1000+ branded exhaust which doesn't = more power compared to custom free flow exhaust system.
Before
The original exhaust on the yaris and vios are very restrictive with a valve system that only opens up at high rpm to ensure good low end torque and minimal sound.
After
To free up the exhaust which in turns more power and without excessive noise the yaris uses the Lukey Ultraflo which is proven to free 3hp on the previous vios project. The exhaust is has a 2in inlet and 2in outlet and is a straight thru muffler.