Cam Profile Design Class - lesson 5

A little more information on the input data.

DURATION - The duration at .050 and the lift are usually already known inputs when designing a cam profile. The duration input number will adjust the duration of the profile. Generally the focus is the duration at .050 but it can be anywhere. The angle on the lift table is 1/4 of the crankshaft duration.

NOSE ACCELERATION - The nose acceleration is the lowest acceleration at the nose of the lobe (0-degree). The velocity is decreasing to zero so the nose acceleration is a negative number. The number is usually between -.00015 and -.00035. Changing this number will change the entire profile. Nose acceleration is a main input.

RAMPS - The input numbers for the ramps were mentioned in lesson two. The valve closing velocity is usually under 40-inches per second for a modern high-end valve train. Other applications are around 30-inches per second. Tappet lash opening velocities are usually less than .002-inches per degree for a solid tappet. The same ramps can be used with different profile designs. New ramps do not have to be designed for each profile. Save your ramp designs.

DATA POINT - This is not necessary to design the lobe, it is just for information. It is the tappet lift at top dead center depending on the indexing of the camshaft in the engine. The angle on the lift table is 1/2 of the crankshaft angle.

OFFSET - Amount the lifter bore is machined with a rotational offset to the camshaft lobe. Can be a positive or negative number. Use 0.000 unless the offset is known.

EXPONENTS - Used in the mathematical equations in the program to design the cam profile. Changing any exponent will generally affect the entire profile. Each exponent must be different. The first exponent is usually the number two. Exponents are main inputs.

My lobe design form will give me the duration, lift, base circle diameter, hydraulic or solid profile, flat or roller tappet, rocker arm ratio, some engine details and the application. That gives me all the information to design the lobe profile. If you like to work with valve lift data, that's fine, just use your valve lift curve and rocker arm ratio and work backwards.

The duration input number will determine the duration at .050 (or anywhere). This number is also the angle on the lift table where the ramp and the profile meet. If the ramp has a height of .020, the duration input number will also be the duration at .020. The nose acceleration and the exponents will be the inputs used to "fine tune" the cam profile. The other inputs have already been determined and will not generally need to be changed. As you can see there is no "magic" involved in this. Just a bunch of numbers that will make up the lift and duration of the lobe profile. The velocity, acceleration, and jerk numbers are important to look at and understand how they affect the profile. Any magic is in the cam designer's knowledge and experience.

The last and most important step is to make the camshaft. If you are a camshaft grinder, use the lift table to make a model lobe and then a master plate or send the lift table to someone that can CNC a master plate for you. If you have a CNC cam grinder, you know what to do. If you are not a camshaft grinder, send the lift table to someone that can manufacture the camshaft for you. Below is my valve timing sheet to go with the finished camshaft ground on 108-degree lobe separation with 3-degrees advance.