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I read the following question recently:
What is it about performance cams that make engines produce more power when they are installed?
I know there are a few components for cars that have "cam" in the name, like "camshaft", "cam belt", "cam sensor", "reversing camera" etc.
What exactly do they mean by "performance cams" and how do they increase power output from the engine?
in its most generic sense converts rotary motion into linear motion or vice versa using solid egg-shaped actuators (lobes)¹.
refers to the shaft which houses a series of cams that actuate the opening/closing of the intake and exhaust valves on a four-stroke engine.
is just a camshaft whose lobe profile is tailored to utilize more of an engine's potential.
Here is a visual comparison²:
The performance improvement can come from two types of change:
altered valve lift
usually a higher lift on the lobe, which increases in length of the valve stroke, which allows for more air to enter through the inlet valves, increasing the power potential of the engine.
altered valve timing - essentially modify when the valves open and close, which has an impact on the effective compression ratio, power output, emissions and other things.
Here is a neat diagram summarizing lots of camshaft-related terminology³:
For several possible reasons. :
the existing camshaft is well-optimized
something else is limiting the engine's potential
ECU maps are not taking advantage of the hardware change
The key thing to remember here is that engine power isn't totally reliant on a single component in most situations. It's usually all about how the different component play in harmony with one another.
¹ - Wikimedia, ² - bestservis.com, ³ - rbracing-rsr.com
Performance cams have various cam lobe configurations where the valve lift and duration are changed from OEM to provide better efficiency for the combustion process.
I would like to make a distinction between efficiency for the combustion process and efficiency of fuel consumption.
Combustion efficiency can be related to how much air and fuel can get into the engine and provide more power.
Fuel consumption efficiency is the attempt to use less fuel.
With more duration and valve overlap you can get better volumetric efficiency.
the volume of air -fuel mixture drawn into the cylinder at atmospheric pressure during the intake strokes compared to the volume of the cylinder, is known as volumetric efficiency
High Performance camshafts;
can push a valve deeper into the combustion chamber and open the poppet a bit more to allow freer flow of gasses.
can leave the valve open for a longer period of time to allow more gasses to flow.
can be configured with a degree wheel and dial indicator to have more valve overlap to flush the combustion chamber of spent exhaust gas.
can be timed and have slots on them to change their relation in time to a partner camshaft (DOHC) or the crank.
can be timed for various LSA's to achieve some of the above configurations.
