By now, you have probably heard a mechanic or automotive enthusiast tell you that an engine is basically one large air pump. Basically, the more air an engine can suck in to combine with fuel, the more power it can create through combustion. It also follows that the more efficiently an engine can remove exhaust gases from the cylinders, the better it can manage that power. Air flow from one end to the other is key to a healthy, strong engine.
The powerful 5.7L V8 features dual VVT-i technology.
Air flow is affected by many different components in the motor, but the valves in the cylinder head are what directly control the amount of air entering a cylinder and the volume of exhaust gases leaving it. The intake valves open up just prior to combustion in order to allow air to flow in and mix with fuel, and the exhaust valves open after the ignition of this mixture in order to suck out the resulting gases. The timing of the valves is controlled by a rotating shaft called the camshaft. The camshaft has lobes which push up on the valves in order to open them and drop them back closed again. How long these valves remain open, and at what point in the combustion cycle, can have a big impact on the drivability and power generated by an engine.
Unfortunately, street vehicles are a compromise between reliability, fuel efficiency and power. While race vehicles have engines with camshaft designs that generate large amounts of power while being used only at specific, high revolutions, your daily driver sees a wide range of rpm’s that make a broader power band necessary. While it is ok for a race car to have a lumpy idle that barely runs below 1000 rpm, it would do you no good if your street car stalled out at every stoplight. Regular vehicles usually have to make do with a camshaft that provides a good amount of power in the most often used range of engine rpms, but runs out of steam at high speeds.
Automakers have addressed this concern with something called “variable valve timing” (abbreviated VVT). The Toyota Tundra uses a variation of variable valve timing called VVT-i in the new 5.7 liter i-Force V8. Instead of relying exclusively on a standard camshaft, VVT-i can vary the timing of the valves in relation to engine speed. It does this by using engine oil pressure to move the camshaft slightly so that more aggressive lobe designs are used when the engine is running at a higher rpm. By doing this, the i-Force V8 is able to run a camshaft profile that provides good fuel efficiency in every day driving, but is still able to churn out gobs of power when the pedal is pressed to the floor.
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 rpm’s 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 as low as 3600. Not only that, 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.
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20 mpg 5.7 i-force? What are you dreaming try 12 at the most