Page 541 - Cam Design Handbook

THB16 9/19/03 8:04 PM Page 529

CHAPTER 16

AUTOMOTIVE CAMSHAFT
DYNAMICS

Dimitri Elgin
D. Elgin Cams
Redwood City, Calif.
www.elgincams.com

16.1 BACKGROUND 529 16.3.2.2 Ductile Iron 535
16.2 INTRODUCTION 531 16.3.2.3 Miscellaneous Materials 535
16.3 CAMSHAFT MATERIALS 531 16.3.2.4 Roller Follower 535
16.3.1 Sliding Follower Camshafts 532 16.4 CAMSHAFT CURVES 535
16.3.1.1 Cast Iron 532 16.5 CAMSHAFT PROFILE GEOMETRY 536
16.3.1.2 MIiscellaneous Materials 534 16.6 HARMONIC ANALYSIS 537
16.3.2 Roller-Follower Camshafts 534 16.7 ENGINE PERFORMANCE 541
16.3.2.1 Steel 534 16.8 SUMMARY 541

16.1 BACKGROUND

It is established that the automotive camshaft is the most influential component that
governs how the engine can perform. The choice of camshaft (cam shape) has a respon-
sibility, reliability, and durability as well as a performance impact.
Before designing the cam lobes (intake and exhaust) one must consider what the engine
“wants” for a timing event diagram—seat-to-seat timing. One must address the physical
limitations such as piston to valve clearance, valve-to-valve clearance, follower con-
straints, and spring limitations. There are at least 25 items to consider in designing the
actual cam lobe (Fig. 16.1).
The writer has had the distinct advantage of having worked with two of the pioneers
on the subject of automotive valve cams, Ed Winfield and Cliff Collins. These men mod-
ified the primitive circular arc and tangent cam profiles by adding ramps and reducing
jerk. In addition they were aware of the demand for air and fuel in the engine and maxi-
mized the “area of the displacement the curve” at the valve to maximize the flow of all
gases. Another development was the effective performance of the valve spring. Valve
springs were always the limiting factor as to how much valve acceleration could be applied
(positive and negative). Custom racing valve springs of silicon chrome wire were initi-
ated as an improvement of the engine performance over its range of speeds.
With the advent of the computer one can simulate the engine, look at the piston
and valve motion, calculate the air demand, and size the intake and exhaust systems.
It has been observed that the computer modeling methods utilized in this chapter can
predict the horsepower and torque values within about 2 to 5 percent of that of the actual
engine.
Also, it is not the horsepower of the engine that wins races but the amount of torque
and horsepower under their respective curves that accelerates the automobile and makes
it a winner. Also, one might say that the automotive cam functions to make the engine
“breathe.”

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