Editing Variable valve timing (section)

{{Short description|Process of altering the timing of a valve lift event}}
{{Use dmy dates|date=October 2020}}
[[Image:K20 head.jpg|thumb|Cylinder head of Honda [[Honda K engine|K20Z3]]. This engine uses continuously variable timing for the inlet valves]]

'''Variable valve timing''' ('''VVT''') is the process of altering the timing of a [[Poppet valve|valve]] lift event in an [[internal combustion engine]], and is often used to improve performance, fuel economy or emissions. It is increasingly being used in combination with [[variable valve lift]] systems. There are many ways in which this can be achieved, ranging from mechanical devices to electro-hydraulic and [[camless]] systems. Increasingly strict emissions regulations are causing<ref>{{Cite web |last=US EPA |first=OAR |date=2016-09-09 |title=Regulations for Greenhouse Gas Emissions from Passenger Cars and Trucks |url=https://www.epa.gov/regulations-emissions-vehicles-and-engines/regulations-greenhouse-gas-emissions-passenger-cars-and |access-date=2022-07-12 |website=www.epa.gov |language=en}}</ref> many automotive manufacturers to use VVT systems.

[[Two-stroke cycle|Two-stroke]] engines use a [[Two-stroke power valve system|power valve system]] to get similar results to VVT.