Unconventional Valve Trains

The majority of my cam profile designs are for conventional valve trains. Meaning the valve lift is a constant ratio compared to the cam profile lift. An example would be if the rocker arm ratio were 1.5 to 1, the valve lift would be the cam lobe lift multiplied by 1.5 at any point. Push rod engines with a rocker arm and overhead cam engines with a direct acting tappet are examples of a conventional valve train. Unconventional valve trains have a ratio that will vary through the valve movement or a cam lobe shape that is not typical. Overhead cam engines with finger followers are an example of a ratio that will vary. A Desmodromic valve train is also unconventional and very interesting. I would recommend studying this valve train. There are a few other older valve trains that are unconventional, but are not used in modern engines. They are still worth studying. You cannot fully understand something without knowing the history and its evolvement. Early internal combustion engines did not have an intake cam lobe and only used an exhaust lobe that opened at the bottom of the exhaust stroke and closed at the top. The intake valve used atmospheric pressure and a valve spring to open and close. To go from no intake cam to what we have today, is an interesting and educational journey.

Different cam profile design programs are written for the different valve train designs. Each program is costly and has to be justified based on the demand for certain profile designs. Much of the input data for these unconventional cam profile designs consists of angles and dimensions for that particular valve train. This data is usually not known and is not easily measured. Having the program only solves part of the problem. Usually a blueprint of that valve train is also necessary. Good luck getting that! Many times, if the customer can plot a ratio table of cam lift to valve lift in 1-degree increments, I can design a cam profile.