The newest approach (which really isn't new) in roller camshafts is to use a larger journal diameter and/or a larger roller wheel diameter. In order to get the performance gains, the cam profiles must be designed for these diameters. Many times they are not.

Years ago when flat tappet mushroom lifters were first being used, cam grinders would often times use profiles that were not designed for the larger lifter diameter. Sometimes the engine builder would install the larger diameter lifters without changing the camshaft. In reality when this was done, there was no difference in performance, other than what was perceived by the racer. Many times things are wrongly done because lack of knowledge and are not intentional.

Today, the same thing is being done with roller camshafts. The cam profiles on these camshafts are not designed for the base circle diameter of the lobe or the roller wheel diameter that is being used. Unless you are being assured by your camshaft grinder that the profiles were indeed designed for the new larger journal or larger roller wheel diameters, chances are the profiles were originally designed for a standard size lobe and roller wheel. Just as with everything, the consumer must be knowledgeable and ask questions.

When a different size lobe or roller wheel diameter is used, the contact point between the lobe and the wheel changes. This changes the velocity, acceleration, jerk, radius of curvature, and the pressure angle from what the original design was. Sometimes no mechanical harm is done, but sometimes mechanical problems do occur. Premature wear to the roller lifter and valve spring problems are the most common problems. Even with no mechanical problems, the performance is not up to where it should be. Just because something works or is adequate doesn't mean that the process is correct. The best engine power is made when a combination of components are designed to work together.

No matter what anyone wants to tell you, the difference between one properly designed profile and another is the area under the lift curve. Take the following example of two profiles being compared and they both have the same lobe lift and the same duration at 0.050. The profile with more duration at 0.100, 0.200, 0.300, and so on would be the better profile. This profile would have more area under the lift curve. Very seldom will you see these higher lift duration figures published unless the cam grinder is very confident in his profiles. The lash setting will also play a part when comparing profiles. A wider lash setting will use up more of the area than a narrow setting. The cam profile and the proper lash setting will tell the whole truth. Remember, I started out by saying properly designed profiles. A profile can be designed with more duration at the higher lifts (more area), but the profile may be too aggressive for the application, and can actually damage the valve train. My approach is to balance more lift area with smoothness and reliability of the valve train.