I'm interested in buying a mk IV 1.8t and i have heard somethings about the engine changing somehow from 01 to 02.

1.What is changed on then engine to get to 20 or 30 extra hp?

2. Are all 02's with the newer engine? (i've heard some 02's didn't change)

3. and if all the 02's didn't get the better engine, what do i look for when i look at the car to determine the differences?