Speaker 1: Welcome to Brainstuff from house Stuff Works dot com where
Speaker 1: smart Happens. Hi Am Marshall Brain with today's question, what
Speaker 1: does it mean when a car has dual overhead cams? Generally,
Speaker 1: engines with dual overhead cams or d o hc are
Speaker 1: higher performance engines. They produce more power and they can
Speaker 1: run at higher speeds. The camshafts have the job of
Speaker 1: opening the valves that let air into an exhaust out
Speaker 1: of the engine. The camshaft uses rotating lobes called cams
Speaker 1: that push against the valves to open them. Springs on
Speaker 1: the valve return them to the closed position. This is
Speaker 1: a critical job and can have a great deal of
Speaker 1: impact on the engine's performance at different speeds. The main
Speaker 1: benefit of dual overhead cams is that they allow an
Speaker 1: engine to have four valves per cylinder. Each camshaft operates
Speaker 1: two of the valves on a cylinder. One camshaft handles
Speaker 1: the intake valves, the other one handles the exhaust valves.
Speaker 1: Having four valves per cylinder gives an engine two big advantages. First,
Speaker 1: by having four valves in a cylinder instead of two,
Speaker 1: a larger portion of the area can be used to
Speaker 1: let air in an exhaust out. The engine can make
Speaker 1: more power if more air enters the cylinder, and it
Speaker 1: weighs less power if it's easier to pump the exhaust
Speaker 1: out of the cylinder. At higher engine speeds, the engine
Speaker 1: pumps a lot of air through these cylinders. Having four
Speaker 1: valves per cylinder allows the engine to pump enough air
Speaker 1: to run and make useful power at these higher speeds.
Speaker 1: A second interesting thing that some car makers do is
Speaker 1: to have a separate intake runner for each of the
Speaker 1: two intake valves in each cylinder. One of the intake
Speaker 1: runners is wide and short for maximum airflow, and the
Speaker 1: other is a tuned intake runner. When the intake valve
Speaker 1: is open on the engine, air is being sucked into
Speaker 1: the engine, so the air and the intake runner is
Speaker 1: moving rapidly towards the cylinder. When the intake valve closes suddenly,
Speaker 1: this air slams to a stop and stacks up on itself,
Speaker 1: forming an area of high pressure. This high pressure wave
Speaker 1: makes its way up the intake runner away from the cylinder,
Speaker 1: and when it reaches the end of the intake runner
Speaker 1: where the runner connects to the intake manifold, the pressure
Speaker 1: wave bounces back down the intake runner. If the intake
Speaker 1: runner is just the right length, that pressure wave will
Speaker 1: arrive back at the intake valve just as it opens
Speaker 1: for the next cycle. This extra pressure helps to cram
Speaker 1: more air and fuel mix into the cylinder, effectively acting
Speaker 1: like a turbocharger for moral This and thousands of other
Speaker 1: topics because it how staff works. Dot Com