Cams Specs | Learn About Cam Lobe, Cam Lift and Cam Duration

Summary

In this video, Mike from Summit Racing explains the key specifications of camshafts, focusing on lift, duration, and lobe separation. He breaks down how cam lift impacts engine performance, explaining the difference between lift at the cam and lift at the valve. The video also covers the concept of cam duration and its relationship to crankshaft rotation, clarifying the differences between advertised and at-50 duration measurements. Finally, Mike explores the importance of lobe separation in determining engine idle quality, vacuum, and power range, offering tips on how to choose the right camshaft for specific engine applications.

Takeaways

• 😀 Cam lobes play a crucial role in controlling the valve train components and affecting key engine characteristics like lift, duration, and even the mechanical fuel pump or distributor.
• 😀 Camshaft lift refers to the distance between the heel and peak of the cam lobe, with lift at the cam being smaller than lift at the valve due to the rocker ratio.
• 😀 Rocker ratio in push rod V8 engines helps to compensate for cam lift, preventing the camshaft from becoming too large to fit into the engine.
• 😀 Duration is the amount of time the valve is open, measured in crankshaft degrees, with a full revolution of the camshaft equaling two revolutions of the crankshaft.
• 😀 Camshaft duration is measured using a 720-degree base instead of the standard 360 degrees, allowing for higher cylinder pressure with larger camshafts.
• 😀 Camshaft manufacturers provide two duration specs: advertised duration (from lift point) and duration at 50 thousandths (from peak lift), the latter making comparisons across manufacturers easier.
• 😀 The at-50 duration standard ensures accurate comparisons by requiring a camshaft’s duration to be measured from 50 thousandths before and after peak lift.
• 😀 Lobe separation angle measures the degrees between the peak lifts of intake and exhaust lobes on the same cylinder, significantly impacting engine characteristics.
• 😀 A smaller lobe separation angle (e.g., 106-108 degrees) results in a rough idle, low vacuum, and power that peaks in the mid-to-high RPM range.
• 😀 A larger lobe separation angle (e.g., 112-114 degrees) produces a smoother idle, better vacuum for accessories like power brakes, and more low-end torque, with power arriving sooner and spanning a broader RPM band.

Q & A

What is the primary function of a camshaft in an engine?

The camshaft controls various components in the engine, including the valve train, mechanical fuel pump, and distributor. It determines how the engine's valves open and close, affecting performance characteristics.

What is the difference between lift at the cam and lift at the valve?

Lift at the cam is the difference between the heel and peak of the cam lobe, whereas lift at the valve refers to the actual movement of the valve, which takes into account the rocker arm ratio. Lift at the valve is typically larger due to the mechanical multiplication from the rocker arm.

Why is lift at the cam always smaller than lift at the valve?

Lift at the cam is smaller because it does not account for the rocker arm ratio, which amplifies the lift at the valve. Without this ratio, the cam lobe could be too large to fit within the engine's block.

What does the term 'duration' refer to in camshaft specifications?

Duration refers to the amount of time the valve is open, measured in crankshaft degrees. It is based on a 720-degree cycle, as the camshaft rotates once for every two rotations of the crankshaft.

What is the difference between 'advertised duration' and 'duration at 50'?

Advertised duration was the original spec used by camshaft manufacturers, but it was based on various lift points, making comparisons between camshafts difficult. Duration at 50 is the modern standard, measured at 50 thousandths of lift to ensure a consistent and comparable specification between different manufacturers.

How does the duration at 50 standard improve comparisons between camshafts?

The duration at 50 standard allows for apples-to-apples comparisons across manufacturers because it uses a consistent measurement method, ensuring that camshafts with similar duration values are comparable regardless of the manufacturer.

What is lobe separation in a camshaft, and why is it important?

Lobe separation refers to the angle between the peak lifts of the intake and exhaust lobes on the same cylinder. It is important because it significantly affects the engine's idle quality, vacuum, and RPM range.

How does a narrower lobe separation (106 to 108 degrees) affect engine performance?

A narrower lobe separation typically results in a rough idle, low vacuum, and a higher RPM range where the engine performs better. It is suited for performance engines that prioritize higher RPM power delivery.

How does a wider lobe separation (112 to 114 degrees) impact engine behavior?

A wider lobe separation leads to a smoother idle, better vacuum (which is useful for power brakes), more low-end torque, and quicker power delivery, creating a broader RPM range for better overall performance.

What are some factors that camshaft specifications like lift, duration, and lobe separation impact?

These specifications affect key engine characteristics such as idle quality, engine vacuum, RPM range, low-end torque, and overall power delivery. Adjusting these specs allows tuning of the engine to suit specific performance goals.