What Is a VVT-i Engine?

Key Points

• Variable Valve Timing-Intelligence, or VVT-i, is a variable valve-timing system developed by Toyota that debuted in the 1990s.
• VVT-i uses input from sensors and driving conditions to improve engine performance, emissions and fuel economy.

VVT-i is short for Variable Valve Timing-Intelligence, an early version of Toyota’s variable valve-timing system that came to be offered on many of the company’s engines.

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What Is Variable Valve Timing?

• Key Takeaway: Introduced to production vehicles in the 1980s, variable valve timing adjusts when the engine’s valves open and close to benefit performance, fuel economy or emissions.

Variable valve timing allows the valves to be opened and closed earlier or later to benefit fuel economy, emissions or power. Otherwise, valve timing is set at a fixed opening and closing that is typically a compromise between the three.

Most early variable valve-timing systems incorporated a mechanism that allowed some rotational movement between the outer rim of the camshaft pulley or sprocket (which is driven by the timing belt or chain) and its center hub that is attached to the camshaft; normally, this was just a solid one-piece unit. That movement allowed the valves to be opened and closed earlier or later depending on driving conditions.

While variable valve timing was introduced to production cars in the 1980s, Toyota didn’t offer the technology until the 1990s. The company’s earliest system, called WT, operated only on the intake valves, with timing varied in only two steps.

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Benefits of VVT-i

• Key Takeaway: VVT-i allows for more precise timing as it uses information from various sensors and driving conditions. Toyota claimed the system improved fuel economy by 6% and torque by about 10%.

VVT-i was the second generation of Toyota’s variable valve timing system. The system brought valve timing that was not only fully variable, but was controlled by a computer (hence the “-i” meaning “intelligence”) using driving conditions and information provided by various sensors. This allowed for more precise timing adjustment. The computer varied the amount of oil pressure fed to the mechanism between the outer and inner portions of the pulley that allowed the intake-valve timing to be advanced or retarded to benefit power, fuel economy or emissions. Toyota claimed that VVT-i could increase fuel economy by about 6% and low-to-mid-range torque by about 10%.

For instance, beginning to open the intake valve a little early — before the exhaust valve is fully closed on the exhaust stroke, a condition referred to as “valve overlap” — reduces exhaust emissions and improves fuel economy. However, that comes at the expense of maximum power. Having the ability to adjust that intake-valve opening based on driving conditions (you don’t need maximum power in normal driving, only when strong acceleration is called for) allows for the best of both worlds. 

Later versions of Toyota’s variable valve-timing system were even more sophisticated. Dual VVT-i added variable timing to the exhaust valves in addition to the intake valves, while VVT-iE replaced the oil-pressure-controlled mechanism with an electric one. VVTL-i added the ability to control the lift of the valves (how far they opened) in addition to the timing of opening and closing.

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