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by: JasonLancaster
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By now, you have probably heard a mechanic or automotive enthusiast tell you that an engine is essentially a 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 the key to a healthy, strong engine.

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.

The amount of time these valves stay open, and at which point in the combustion cycle they are open, can strongly impact the drivability and power of an engine. If you want a really fast car, like a race car, you'll need to adjust the camshaft to perform well at the high RPMs needed for a powerful engine. This will mean poor performance at low RPMs, which isn't a problem for race cars. If you're looking for something with a lot of low-end torque, such as for towing, then you should adjust the camshaft accordingly to perform at low RPMs. Of course, this will also mean sacrificing high RPM performance.

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 types of camshafts obviously aren't too efficient. Since they're trying to do everything adequately, they don't really do any one of them superiorly. Your engine needs to be able to perform just as well accelerating from a stop as it does speeding down the highway, which means that much of the time, it's burning too much fuel and also underperforming.

Automakers have developed something called "variable valve timing" (VVT) to address this problem. Toyota's newest VVT-i engine, the Toyota Tundra's i-Force 5.7L V8, can vary the timing of the valves to match engine speed. It uses engine oil pressure to make slight adjustments to the camshaft, so that more aggressive lobe designs are used when working at higher RPMs. This makes the i-Force capable of running a camshaft configuration which provides fuel efficiency for everyday driving, but that can still turn out lots of power when you press the pedal to the floor.

The dual VVT-i in the Toyota Tundra goes even further - at high RPMs, it allows the exhaust and intake valves to open at the same time, which scavenges airflow as much as possible. The result? A V8 engine that can produce 381 horsepower at 5600 rpm, but also generate 401 lb-ft of torque at as little as 3600 rpm. And what's more, the 2 wheel drive Tundra can still get a respectable 20 miles per gallon on the highway. Possibly the best part about Toyota's variable valve timing system is getting killer horsepower without getting killed at the pump.

About the Author

Author Jason Lancaster is the editor of TundraHeadquarters.com, a website with information, news, and reviews of Toyota Tundra accessories and Tundra parts.

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