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Variable Valve Timing

Car culture term

Variable Valve Timing
Photo: Joe Flores / Wikimedia Commons · CC BY-SA 3.0

What is Variable Valve Timing?

A technology that continuously or step-changes the timing of intake and exhaust valve opening events relative to crankshaft position, broadening an engine's power and torque delivery across the RPM range.

Variable valve timing (VVT) allows an engine's camshaft(s) to be phased forward or backward relative to the crankshaft as the engine operates. By advancing or retarding cam timing under computer control, engineers can optimize the overlap between intake and exhaust valve opening events for different conditions. More overlap at high RPM and load improves power; less overlap at idle and light load improves fuel economy and idle quality.

The technology became widespread through the 1990s and 2000s. Toyota's VVT-i (Variable Valve Timing-intelligent), introduced 1996, was among the earliest mass-market implementations. BMW's VANOS, Porsche's VarioCam, Nissan's CVTC, and Ford's Ti-VCT all followed related principles. Honda's VTEC combines variable lift switching with phase control in its i-VTEC system. Most modern naturally aspirated and turbocharged engines use some form of VVT on both intake and exhaust camshafts (dual VVT).

Variable valve timing is fundamentally different from variable valve lift (like VTEC's lift-switching). Timing changes the phase of events; lift changes how far the valve opens. Premium systems like BMW's Valvetronic and Fiat's MultiAir vary both continuously. The net result across the industry has been broader torque curves, improved fuel economy, and reduced emissions without sacrificing peak power output.

Related terms

VTECNaturally aspiratedCamshaftRedlineDirect InjectionTurbo

Frequently asked questions

What is the difference between VVT and VTEC?
VVT (in its basic form) phases the camshaft continuously for timing optimization. VTEC switches between two different cam lobe profiles for a step change in valve lift and duration. VTEC is a lift-switching system; traditional VVT is a phasing system. Honda's i-VTEC combines both. Other manufacturers have developed their own variable lift systems (BMW Valvetronic, Fiat MultiAir) on top of cam phasing.
Does VVT increase horsepower?
It enables higher peak power relative to what a fixed-timing engine of the same displacement could achieve, while also improving low-RPM torque. The practical effect is a broader usable power band. VVT does not add power so much as it optimizes the engine's ability to breathe efficiently across a wider operating range.
Can VVT fail?
Yes. The variable cam timing actuator (phaser) is a mechanically complex component driven by oil pressure. Dirty oil, low oil pressure, or sludge buildup can cause phaser malfunction. Symptoms include rough idle, P0010/P0014-series fault codes (cam timing codes), and reduced performance. Regular oil changes are the primary preventive maintenance for VVT longevity.
Do turbocharged engines use VVT?
Yes, widely. Modern turbocharged engines benefit substantially from VVT because they can spool the turbo more aggressively by adjusting exhaust cam timing, and use intake timing to optimize charge scavenging at boost. High-performance turbo engines like the BMW S58, Ford 2.3 EcoBoost, and many others use dual-VVT.
What is dual VVT?
Dual VVT (or Dual VVT-i, Dual VANOS) applies variable timing to both the intake and exhaust camshafts independently. Single VVT only phases the intake cam. Dual VVT offers more precise control over valve overlap and scavenging, resulting in better fuel economy and broader power delivery. Most modern performance engines use dual VVT.

Variable Valve Timing on the blog

Did the Lotus Elise have a Toyota engine?
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Yes. Lotus started putting Toyota engines in the Elise in 2004, and Toyota power stayed until production ended in December 2021. The first Elises used a Rover K-Series. Here are the Toyota engines Lotus used, the Toyotas they came from, and why the switch happened.

What Is VTEC, and why do people Yell about it?
What Is VTEC, and why do people Yell about it?

VTEC is Honda's variable valve system, and it is why so many Honda engines feel like two engines in one: calm and efficient at low rpm, then suddenly frantic up top. That switch is the moment behind the famous meme, and here is what is actually happening when VTEC kicks in.

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