Crazy Cam Profiles

Once in a while I will get involved in designing a cam profile that does not follow the usual parameters of lobe design. I call these "crazy cam profiles". Some of you may remember Rod Serling saying "you have just crossed over into the twilight zone" from the TV series. That is my feeling about these cam profiles.

These cam profiles are usually (but not always) used in applications with valve lift rules combined with low RPM engines and low valve spring pressures. These types of engines are very forgiving of the lobe profile design and allow you to get away with stuff that you normally could not.

One of the craziest lobe profiles I have seen involves designing a lobe with a lot of lift and then grinding away the excess lift to comply with the lift rule. This creates a lobe with much more duration than could be designed normally. The finished lobe looks awful on paper but works fine in the real world. The usual ways to create crazy cam profiles are by modifying the lift table, modifying the actual lobe, or just designing a radical profile. These crazy cam profiles are more common than you would think. These profiles have velocity, acceleration, and jerk curves totally different from a normal cam profile. The maximum values are usually much higher and the shape of the curves are fairly erratic. It is difficult to do but all the normal basic lobe design rules must be ignored.

These profiles are a good example of the "design world" and the "real world". As a lobe designer, it's good to get involved with these profiles. They teach you a lot about what you can get away with in the real world. Some of the stuff is very surprising.