Toyota VVT-i System

Toyota VVT-i System


Any mechanic or automotive enthusiast can tell you that an engine is essentially a large air pump. The more an engine can suck in air to mix with fuel, the more it can create power through combustion. Thus, the more efficiently an engine removes exhaust gases from the cylinders, the better it can manage that power. The key to a strong, healthy engine is adequate air from one end to another.

Many different things can affect air flow in a motor, but the primary control over the volumes of air entering a cylinder, and exhaust leaving it, comes from the valves in the cylinder head. The intake valves open immediately before combustion to allow air to flow in and combine with the fuel. After this mixture has been ignited, the exhaust valves open and suck out the resulting gases. Valve timing is controlled by the camshaft, which is a rotating shaft with lobes pushing up on the valves to open them, then drop them closed again.

An engine's drivability and power can really be affected by length of time and the point in the combustion cycle at which the valves are open. A really fast car, such as a race car, will need an engine that produces lots of power at high RPMs. To get this, the camshaft can be adjusted to perform well at higher RPMs, but the trade-off will be poor performance at low RPMs. Following the same principle, adjusting the camshaft to perform best at low RPMs will give you lots of low-end torque, which is great for jobs like towing, but your high RPM performance will suffer.

Unfortunately for street vehicles, they need to be a compromise between reliability, fuel efficiency and power. Vehicles like race cars, which perform within a specific range of RPM, can afford to have poor performance outside their optimal RPM, in return for large amounts of power and high performance at their ideal RPM range. Street vehicles, however, need to function over a large range of RPMs. It would be no good if your street car stalled at every traffic light or ran out of steam whenever you tried to take the highway! Regular vehicles need to use a camshaft design that provides adequate power in the most often used range of RPMs.

These compromise camshafts aren't terribly efficient. Because they try to do so many things - from accelerating your car from a dead stop to providing performance at highway speeds, and everything in between - they don't do any one of them very well. This means that your engine burns too much fuel most of the time, while also underperforming.

Automakers know about this problem, and have created something called "variable valve timing" (VVT) in response. The Toyota Tundra's i-Force 5.7L V8, Toyota's newest VVT-i engine, can use engine oil pressure to move the camshaft slightly, so that the timing of the valves can be adjusted in relation to engine speed. This way, more aggressive lobe designs can be used when the engine is working at a higher RPM. The VVT system allows the i-Force V8 to run a camshaft profile that gives good fuel efficiency in regular driving, but that can also crank up the power when it's called for.

The dual VVT-i in the Tundra takes things a step further by allowing the exhaust and intake valves to open at the same time at very high RPMs in order to scavenge the airflow as much as possible. This all adds up to a V8 engine that produces 381 horsepower at 5600 rpm while still generating 401 lb-ft of torque at as low as 3600 rpm. Not only that, but in the 2 wheel drive models, the Tundra gets a respectable 20 miles per gallon on the highway. Perhaps most importantly, Toyota's variable valve timing system lets you have killer horsepower without getting killed at the gas pump.