UFO Sightings

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.

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.

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.

Street vehicles are a compromise between reliability, fuel efficiency and power, which can RPM performance, but street vehicles need a broader power band because they function at a wide range of RPMs. A race car can get away with an idle that barely runs below 1000 RPM, but you can’t have a street car that stalls at every stoplight. Everyday vehicles usually compromise with a camshaft that works well at the most often used range of engine RPMs, but don’t deliver at high speeds.

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 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 Tundra’s dual VVT-i goes one step further by allowing the exhaust and intake valves to open simultaneously at extremely high RPMs, to scavenge airflow as much as possible. This results in a V8 engine that can produce 381 horsepower at 5600 rpm, and 401 lb-ft of torque at as low as 3600 rpm - while still getting a respectable 20 miles per gallon on the highway with the 2 wheel drive models. And what’s best is, the Toyota variable valve timing system gives you killer horsepower without killing you at the gas pump.

Filed under: Vehicles