COMP Cams has built a reputation for delivering top-tier performance and precision in internal combustion engines. Known as the “heart” or “brain” of a performance engine, the camshaft plays a pivotal role in determining how a four-stroke engine operates. This article explores key cam timing events — Intake Opening, Intake Closing, Exhaust Opening, Exhaust Closing, and Overlap — and their effects on engine performance.
Intake Opening
Every performance starts somewhere, and for cam timing, it begins with intake opening. This critical event sets the tone for vacuum, throttle response, emissions, and fuel economy. As the exhaust stroke wraps up and the piston nears the top of its travel, the intake valve cracks open. This action starts a siphon effect, pulling the fresh air-fuel charge into the chamber. Timing this precisely ensures a clean slate for the next combustion cycle.
Intake Closing
If there’s one valve timing event you need to focus on, it’s intake closing. This determines when the cylinder begins building pressure during the compression stroke. Close the intake valve early, and you’ll trap more air at lower speeds, boosting low-RPM torque. Delay the closing and you give the intake charge more time to fill the chamber, improving power at high engine speed. It’s a balancing act, and getting it right can make or break engine performance.
Exhaust Opening
The exhaust valve opening is all about clearing out the waste. After the spark plug ignites the air-fuel mixture, the flame front expands, driving the piston downward in the power stroke. Partway through this stroke, the exhaust valve opens, letting the burned gases escape. Adjusting this timing can tweak your engine’s behavior: open earlier for a broader power curve or open later to wring every bit of low-rpm torque out of the combustion process.
Exhaust Closing
As the exhaust gases exit and the piston starts its descent into the intake stroke, the intake valve opens quickly to draw in fresh air and fuel. Here, the exhaust valve needs to close at precisely the right moment to prevent burned gases from re-entering the chamber, while still allowing all the spent gasses to escape. Nail this timing, and you’re setting the stage for a cleaner, more efficient burn in the next cycle.
Overlap
Overlap is where the magic happens. For a brief moment, both the intake and exhaust valves are open simultaneously. This overlap allows the intake and exhaust systems to interact, creating a delicate dance of airflow. Small adjustments here can make big differences, depending on your engine’s combustion chamber design, intake, and exhaust setup. The goal is simple: retain as much of the fresh intake charge as possible while fully expelling the exhaust gases. Precision is everything.
Cam timing isn’t just about numbers; it’s about tuning your engine to perform exactly how you need it to. By understanding and adjusting events like intake opening, intake closing, exhaust opening, exhaust closing, and overlap, you can tailor your engine’s behavior to suit your goals. Whether you’re chasing peak power or smooth efficiency, the camshaft holds the key.