What is variable valve lift? What is variable valve timing? We're going to look at the valvtrain from a 2009 Audi 2.0L I4 Turbo engine to check out the differences. Variable valve lift is used to enhance performance depending on the RPM and load, while variable valve timing is typically used for emissions control (lowering combustion temperatures and thus reducing NOx), but also has performance and efficiency benefits as well. | Engineering Explained

VTEC Demystified: Here's How It Works | Engineering Explained