WEBVTT - What does it mean when a car has dual overhead cams?

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<v Speaker 1>Welcome to Brainstuff from house Stuff Works dot com where

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<v Speaker 1>smart Happens. Hi Am Marshall Brain with today's question, what

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<v Speaker 1>does it mean when a car has dual overhead cams? Generally,

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<v Speaker 1>engines with dual overhead cams or d o hc are

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<v Speaker 1>higher performance engines. They produce more power and they can

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<v Speaker 1>run at higher speeds. The camshafts have the job of

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<v Speaker 1>opening the valves that let air into an exhaust out

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<v Speaker 1>of the engine. The camshaft uses rotating lobes called cams

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<v Speaker 1>that push against the valves to open them. Springs on

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<v Speaker 1>the valve return them to the closed position. This is

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<v Speaker 1>a critical job and can have a great deal of

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<v Speaker 1>impact on the engine's performance at different speeds. The main

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<v Speaker 1>benefit of dual overhead cams is that they allow an

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<v Speaker 1>engine to have four valves per cylinder. Each camshaft operates

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<v Speaker 1>two of the valves on a cylinder. One camshaft handles

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<v Speaker 1>the intake valves, the other one handles the exhaust valves.

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<v Speaker 1>Having four valves per cylinder gives an engine two big advantages. First,

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<v Speaker 1>by having four valves in a cylinder instead of two,

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<v Speaker 1>a larger portion of the area can be used to

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<v Speaker 1>let air in an exhaust out. The engine can make

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<v Speaker 1>more power if more air enters the cylinder, and it

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<v Speaker 1>weighs less power if it's easier to pump the exhaust

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<v Speaker 1>out of the cylinder. At higher engine speeds, the engine

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<v Speaker 1>pumps a lot of air through these cylinders. Having four

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<v Speaker 1>valves per cylinder allows the engine to pump enough air

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<v Speaker 1>to run and make useful power at these higher speeds.

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<v Speaker 1>A second interesting thing that some car makers do is

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<v Speaker 1>to have a separate intake runner for each of the

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<v Speaker 1>two intake valves in each cylinder. One of the intake

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<v Speaker 1>runners is wide and short for maximum airflow, and the

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<v Speaker 1>other is a tuned intake runner. When the intake valve

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<v Speaker 1>is open on the engine, air is being sucked into

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<v Speaker 1>the engine, so the air and the intake runner is

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<v Speaker 1>moving rapidly towards the cylinder. When the intake valve closes suddenly,

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<v Speaker 1>this air slams to a stop and stacks up on itself,

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<v Speaker 1>forming an area of high pressure. This high pressure wave

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<v Speaker 1>makes its way up the intake runner away from the cylinder,

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<v Speaker 1>and when it reaches the end of the intake runner

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<v Speaker 1>where the runner connects to the intake manifold, the pressure

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<v Speaker 1>wave bounces back down the intake runner. If the intake

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<v Speaker 1>runner is just the right length, that pressure wave will

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<v Speaker 1>arrive back at the intake valve just as it opens

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<v Speaker 1>for the next cycle. This extra pressure helps to cram

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<v Speaker 1>more air and fuel mix into the cylinder, effectively acting

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<v Speaker 1>like a turbocharger for moral This and thousands of other

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<v Speaker 1>topics because it how staff works. Dot Com