Symmetrical And Asymmetrical Cam Profiles
If you are new to my blog page, please start at the beginning and read all of my posts. You will have a better understanding of cam profiles and my approach to cam profile designs.
If the cam profile lift table is the same on the opening and closing side, the profile is symmetrical. If the lift table is not the same, the profile is asymmetrical. Simple enough…right? You must study and graph the lift table of any cam profile to truly understand the profile. The lift table is the blueprint of a cam profile.
Most of the early modern cam profile designs were symmetrical. When I speak of modern cam profiles, I mean a computer was used in the design process. Symmetrical profiles were easier to design and the knowledge available, at the time, was just in the beginning stages. Asymmetrical profiles were created when the opening and closing ramps became different. This is because the valve can be opened faster than it can be closed. Most cam profiles today are asymmetrical.
In most conventional cam profiles, the opening and closing ramps are what make the profile asymmetrical. This causes some of the main profile to also be asymmetrical. Usually from the end of the ramp to around .050 tappet lift, the profile will be asymmetrical. As you move up the lift table to maximum lift, the profile will become less asymmetrical. On either side of maximum lift, the profile will actually be symmetrical for many degrees. The major asymmetry is in the low lift areas of the profile. The higher lift areas may be asymmetrical, but not by very much. Again, the only reason the profile is asymmetrical, is that the opening and closing ramps are designed differently. There is no magic going on here to try and manipulate the air flow.
For an unconventional cam profile, the entire opening and closing side of the profile is intentionally designed different. This is because the rocker ratio is not consistent (as in a conventional profile) throughout the valve movement. Usually, you can see the different shape of the opening and closing side of the lobe. This type of profile is highly asymmetrical and must be designed that way for a smooth valve motion.
Conventional symmetrical cam profiles are still designed today. There is nothing wrong with them. Just because a cam profile is symmetrical, doesn’t mean that it is a poor design or inferior.
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