As a senior car enthusiast, I have always been fascinated by the sound and performance of a choppy camshaft. The aggressive rumble and lopey idle of a choppy cam is a signature sound of high-performance engines. But what exactly makes a cam choppy? In this article, I will explain the science behind camshaft design and how it affects the engine's performance and sound.
Camshaft Basics
First, let's start with the basics. A camshaft is a rotating shaft with a series of lobes that open and close the engine's valves. The shape and size of the lobes determine the valve timing, lift, and duration. These factors affect the engine's power output, fuel efficiency, and emissions. Camshafts are typically made of hardened steel and are located in the engine block, above the crankshaft.
Camshaft Profiles
Camshaft profiles refer to the shape and size of the lobes. There are several types of cam profiles, including flat tappet, hydraulic roller, and solid roller. Each type has its own advantages and disadvantages, depending on the engine's application and performance goals.
A flat tappet camshaft has a symmetric lobe shape, which means the opening and closing ramps are identical. These cams are commonly used in older engines and have a simpler design than roller cams. However, they are prone to wear and require frequent maintenance.
Hydraulic roller cams have a convex lobe shape, which allows for greater lift and duration than flat tappet cams. They also have a hydraulic lifter that automatically adjusts valve lash, reducing wear and improving reliability. However, they are more expensive and require a compatible lifter and pushrod setup.
Solid roller cams have a concave lobe shape, which allows for even greater lift and duration than hydraulic roller cams. They also have a solid lifter that provides precise valve control and high RPM capability. However, they require frequent maintenance and are not suitable for street use.
Lift and Duration
The two most important factors that affect a cam's performance are lift and duration. Lift refers to how far the valve opens during the camshaft rotation, while duration refers to how long the valve stays open. These factors determine the engine's airflow and power output.
A high lift cam allows more air to enter the engine, which increases power and torque. However, it also requires stiffer valve springs and may cause valve float at high RPMs. A long duration cam keeps the valves open for a longer period, which also increases airflow and power. However, it may sacrifice low-end torque and drivability.
Lobe Separation Angle
The lobe separation angle (LSA) refers to the angle between the intake and exhaust lobes on the camshaft. This angle affects the engine's idle quality and power characteristics. A narrow LSA (less than 110 degrees) creates a choppy idle and improves top-end power. However, it sacrifices low-end torque and drivability. A wide LSA (more than 110 degrees) creates a smoother idle and improves low-end torque. However, it sacrifices top-end power.
Conclusion
In summary, a choppy camshaft is the result of a combination of factors, including camshaft profile, lift, duration, and lobe separation angle. These factors affect the engine's performance and sound, and each has its own trade-offs. Choosing the right camshaft for your engine requires careful consideration of your performance goals and driving habits. With the right camshaft, you can achieve the perfect balance of power, torque, and sound.