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The Power of Your Cam Card: A Roadmap to Peak Engine Performance

an imagine of a Solid Roller camshaft.
Camshaft


A cam card, also known as a camshaft card or camshaft specification document, offers comprehensive details about a particular camshaft employed in an engine. Camshafts play a vital role in internal combustion engines, governing the opening and closing of intake and exhaust valves. Engine builders and enthusiasts utilize cam cards to grasp the camshaft's specifications and its intended performance attributes.

Cam cards typically include information such as the camshaft's unique part number, the manufacturer's name, lobe separation angle (LSA), duration, lift, intake centerline position, valve timing details, valve lift profile, recommended valve springs, and any additional notes or recommendations.

Engine builders rely on this information to select the appropriate camshaft for their specific needs, be it for street use, racing, towing, or other purposes. Properly interpreting and applying the data from a cam card is essential for ensuring the correct installation and timing of the camshaft, ultimately leading to optimal engine performance.

The centerline of a cam lobe.
Explanation of Centerline

Let us start off with the Lobe center of a camshaft. The lobe center of a camshaft is an exact line that is draw from the highest point of the lobe to the lowest point of the lobe. This is measured between the center of the lobe and Top Dead Center. This angle is fixed and cannot be changed, only altered by moving the center line closer and further away from TDC.

The separation between the intake centerline and the exhaust centerline is known as the camshaft lobe separation angle (LSA), this is a critical parameter that defines the angular relationship between the centerlines of the intake and exhaust lobes on the camshaft. This angle is measured in degrees and has a significant impact on the performance characteristics of an engine.

When a camshaft is ground in a "straight up" position, both centerlines align, resulting in a Lobe Separation Angle (LSA) that is equal to half the sum of their values. It's more common to observe cam companies grinding their street cams with a 4-degree advance to enhance low-end torque, especially in longer-duration camshafts.



Here's what you need to know about the lobe separation angle of a camshaft:


1. Definition: The lobe separation angle represents the angle between the peak points of the intake and exhaust lobes on the camshaft. It is determined by measuring the distance between the centerlines of these two lobes in degrees of crankshaft rotation. The angle can vary for different camshafts and is a fundamental specification that engine builders consider when selecting a camshaft for a specific application.

2. Effects on Engine Performance:

  • Idle Quality: The LSA significantly influences the engine's idle quality. A wider LSA (larger angle) tends to result in a smoother idle, making it suitable for street-driven vehicles, as it reduces roughness and vibrations.

  • Torque and Power: The LSA also affects the engine's torque and power characteristics. A wider LSA typically provides better low-end torque, which can be beneficial for everyday driving and off-the-line acceleration. Conversely, a narrower LSA can enhance high-end power at the expense of low-end torque.

3. Tuning and Application: Engine builders select a camshaft with a specific lobe center angle based on the desired performance characteristics for a particular application. For example:

  • Street Applications: Wider LSAs (e.g., 112-116 degrees) are commonly used for street-driven vehicles to achieve a balance between smooth idle, low-end torque, and overall drivability.

  • Performance and Racing: Narrower LSAs (e.g., 108-110 degrees or even less) are often chosen for high-performance and racing applications to maximize high-end power and performance.



How do we find the intake centerline and the exhaust centerline?


Things you need to know.

Intake opening = degrees

Intake close = degrees

Exhaust opening = degrees

Exhaust closing = degrees


The cam card of the Lunati 40120525.
Lunati Cam Card

Example 1:

Lunati 40120525 .645 in .645 ex

Intake opening = 24.5 degrees

Intake closes = 48.5 degrees

Exhaust opens = 60.5 degrees

Exhaust closes = 20.5 degrees


First, we need to find the Duration of the cam, this is typically on the cam card, but we can use the formula: Duration at specific lift = opening point + 180 degrees + Closing point

Duration at specific intake lift = 24.5 + 180 + 48.5 = 253 degrees

Duration as specific exhaust lift = 60.5 + 180 + 20.5 = 261 degrees



Next, we can use these durations to find our centerlines with the following formula:

Intake center line = (duration / 2) - Intake opening

Exhaust centerline = (Duration / 2) - Exhaust closing

Intake centerline = (253 / 2) - 24.5 = 102 degrees

Exhaust centerline = (261 / 2) - 20.5 = 110 degrees

Finally, we can use the centerlines we just calculated to determine the Lobe separation angle of the cam with the following formula:

Lobe Separation Angle = (intake centerline + Exhaust centerline) / 2

LSA = (102 + 110) / 2 = 106 degrees

Intake centerline is 102 degrees and the LSA is 106 degrees this is a reference to the 4 degrees advanced I was speaking of.


With the lobe separation of 106 degrees, we can determine from a standard practice of LSA information that this cam is more of a performance racing application cam. Can this camshaft be used in a street driven application even though it has a 106 LSA?

Another factor in the cam card profile that needs to be determined for peak engine performance is cam overlap. Camshaft overlap is a crucial parameter in engine tuning and camshaft selection. It refers to the period during which both the intake and exhaust valves are open simultaneously at some point in the engine's cycle. Overlap plays a significant role in an engine's performance and exhaust scavenging.



Here's how you can determine camshaft overlap:


1. Calculate Overlap: Overlap is calculated by finding the overlap angle, which is the period during which both the intake and exhaust valves are open. It's the sum of the intake valve opening (IVO) and exhaust valve closing (EVC) angles: Overlap Angle = IVO + EVC

3. Interpret the Results: The overlap angle obtained from the calculation tells you how many degrees of crankshaft rotation both the intake and exhaust valves are open simultaneously. A larger overlap angle indicates more overlap, while a smaller angle means less overlap.

4. Consider the Effects: Overlap has significant effects on engine performance:

  • Scavenging: Overlap helps exhaust gases flow out of the cylinder and can improve cylinder filling with fresh air/fuel mixture during the intake stroke, enhancing performance.

  • Idle Quality: Increased overlap can result in a rougher idle due to exhaust reversion, which can affect drivability and emissions.

  • Torque and Power: Overlap can influence torque and power characteristics, with more overlap typically favoring high-end power at the expense of low-end torque.

5. Camshaft Selection: When selecting a camshaft, consider the desired performance characteristics. A camshaft with greater overlap can be chosen for high-performance or racing applications to maximize power, while a milder camshaft with less overlap may be preferred for street applications where smooth idle and low-end torque are essential.


For supercharged and turbocharged setups, it's advisable to steer clear of camshafts with excessive overlap. This is because the boosted intake system already efficiently fills the cylinders and assists in scavenging exhaust gases. In such scenarios, prolonged overlap can prove counterproductive as it may allow a portion of the intake charge to bypass the engine without undergoing combustion.


Example 2:

Lunati 40120525 .645 in .645 ex

Intake opening = 24.5 degrees

Intake closes = 48.5 degrees

Exhaust opens = 60.5 degrees

Exhaust closes = 20.5 degrees

Valve Overlap Angle = 24.5 + 20.5 = 45 degrees


Now that we have this let's take it to a chart that was created by David Vizard. The “Overlap Requirement Chart” In this chart he has created 5 overlap sections 1: 10-35 degrees 2: 30-55 degrees 3: 50-75 degrees 4: 70-95 degrees 5: 90-115 degrees.

He continues to explain that in Section 1 pertains to utility trucks, emphasizing the need for robust low-end torque and fuel efficiency. Camshafts with the specified duration on the appropriate Lobe Center Angle (LCA) excel at delivering impressive performance right from idle, ensuring outstanding towing capacity under heavy loads, optimal fuel economy, and a smooth idle. When employing such camshafts, it is imperative to pair them with high-lift rockers since the limited duration restricts the extent to which the cam lobe's lift can be enhanced.

Section 2 caters to everyday vehicles, both cars and trucks, where the primary focus remains on maintaining smooth idling and excellent low-speed performance. This approach ensures pleasant street behavior and robust acceleration from a standstill, especially when equipped with a standard stall converter.

Section 3 is designed for high-performance street vehicles, where top-notch performance takes center stage while preserving respectable street etiquette remains essential. When working in this category, it's crucial to lean towards shorter-duration camshafts rather than overloading the engine with excessive camming, particularly when the vehicle is on the heavier side.

Section 4 caters to oval track racing, intense road racing, and bulkier drag race vehicles.

Section 5 is dedicated to uncompromising drag racing powerplants. In these final two categories, selecting the correct compression ratio is a crucial factor for achieving success.

With this knowledge looking back it is crucial to have the proper LSA with the appropriate overlap for maximizing the engines full potential in the category you intend to use it in. With the Lunati cam we have been using in our examples we see that even though it has a performance ready 106-degree LSA, it has a daily driven overlap of 45 degrees.


What is the difference in the “lift” and the “duration” of a camshaft?


The lift and duration of a camshaft are essential specifications that profoundly impact the camshaft's operation and, by extension, the performance of an engine. These characteristics play distinct roles:

  • Lift: This dimension, often known as valve lift, signifies how far the camshaft pushes open the engine's valves. It is quantified in inches or millimeters and reveals the maximum displacement of the valve from its resting position during one full rotation of the camshaft. Greater lift values translate to wider valve openings, enabling a larger volume of air and fuel to enter the cylinders. This heightened valve lift generally leads to improved engine performance, particularly at higher RPMs.

  • Duration: Camshaft duration, or valve duration, quantifies how long a valve remains open throughout an entire engine cycle, usually expressed in degrees of crankshaft rotation. It encompasses both the period when the valve initiates opening (intake valve opening) and when it initiates closing (intake valve closing) for the intake valve. Similar considerations apply to the exhaust valve (exhaust valve opening and exhaust valve closing). Longer duration results in an extended interval for air and fuel to flow in and out of the cylinders, which can enhance top-end power but may decrease low-end torque.

Is the “lift at valve” on a cam card the actual height of the cam lobe? Can the lift be changed (modified)?

The rocker Arm and the ratio it has.
Rocker Arm



The net valve lift varies depending on the lifter type used. To account for thermal expansion, the system incorporates clearance through clearance ramps and valve lash in the case of solid lifter cams. When dealing with a solid camshaft, you need to subtract the valve lash clearance from the total valve lift to determine the net valve lift.

The "lift at valve" measurement is closely tied to the rocker arm ratio specified on the cam card. In our case, the camshaft is associated with a 1.5 rocker arm ratio. This cam is also a solid roller cam, in this case we have to take into account the valve lash needed. This means that for the Lunati 40120525 cam, the intake net valve lift is rated at 0.645 inches, and the exhaust net valve lift is also rated at 0.645 inches. Therefore, the actual lift provided by the cam lobe itself (40120525) is 0.645 - .020 / 1.5, which equals 0.416 inches.

With this information, we can calculate the overall valve lift for any desired rocker arm ratio. Simply multiply the 0.416-inch lobe lift by the chosen rocker arm ratio. For instance, if we opt for a 1.65 ratio, the modified overall valve lift for this cam becomes 0.416 x 1.65, which equals 0.6864 inches. This represents a 6% increase in the overall valve lift.

Increasing valve lift through this adjustment enables wider valve openings, allowing a larger volume of air and fuel to enter the engine cylinders. This heightened valve lift generally results in improved engine performance, especially at higher RPMs. This is a primary reason why engine enthusiasts often opt for larger rocker arm ratios, particularly on the exhaust valves. A larger ratio permits a greater volume of exhaust gases to exit the combustion chamber, facilitating more efficient air and fuel intake during the intake cycle.

Adjusting valve lash has the effect of increasing lift and initiating the valve's opening earlier, effectively replicating the characteristics of a larger camshaft. However, it's important to exercise caution when making valve lash adjustments, with a maximum limit of .004 inches recommended. Additionally, it's crucial to take into account the clearance between the valves and the pistons before making significant adjustments on the exhaust side. In some cases, a racer might choose to tighten the lash on the exhaust valves if they perceive limitations in exhaust flow. Alternatively, they could opt to adjust the lash on the outer four corner cylinders to compensate for the longer intake runners.



What is the difference in advertised duration and duration at .050?


The difference between the duration at 0.050 inches (often referred to as "duration at 0.050" or simply "at 0.050") and the advertised duration is an important specification when discussing camshafts.

1. Advertised Duration: This is the total duration of the camshaft's lobe profiles as specified by the camshaft manufacturer. It includes the entire time the valve is off its seat, from when it first begins to open until it is fully closed. Advertised duration is typically measured in degrees of crankshaft rotation and is used as a marketing or informational figure to describe the camshaft's characteristics.

2. Duration at 0.050 inches: This is a more specific and standardized way to measure camshaft duration. It represents the duration of the camshaft lobe profiles at the point when the lift has reached 0.050 inches, or 50 thousandths of an inch (approximately 1.27 millimeters). This measurement is considered more consistent and meaningful because it accounts for variations in valve lash and allows for better comparison between different camshafts.

The key difference between these two duration figures is that the duration at 0.050 inches excludes the time when the valve is opening and closing just slightly off its seat (valve overlap), focusing on the time when the valve is in motion and providing significant lift. This value is typically shorter than the advertised duration.


If we can modify the cam lift, can we modify the cam duration?


Camshaft duration, which refers to the amount of time the valve remains open during an engine cycle, is primarily determined by the physical shape and design of the camshaft lobes. It is not something that can be easily modified or enhanced without physically altering the camshaft itself. Modifying camshaft duration typically involves regrinding the camshaft lobes, which is a complex and specialized process that requires advanced machinery and expertise.


In conclusion, a cam card, also known as a camshaft specification document, serves as a crucial resource for engine builders and enthusiasts, offering comprehensive details about a specific camshaft's specifications and performance attributes. Camshafts play a vital role in controlling the opening and closing of intake and exhaust valves in internal combustion engines. By providing information such as part numbers, manufacturer details, lobe separation angles, duration, lift, valve timing, and more, cam cards enable informed decisions in selecting the right camshaft for specific applications.

Understanding the lobe center or lobe separation angle (LSA) is crucial, as it significantly affects engine performance attributes such as idle quality, torque, and power. A correct grasp of LSA ensures that the chosen camshaft is well-suited for its intended purpose, whether it be for everyday street driving or high-performance racing applications. Additionally, determining the overlap of a camshaft, which refers to the period when both intake and exhaust valves are open simultaneously, plays a pivotal role in engine tuning and overall performance. Overlap has a substantial impact on factors like exhaust scavenging, idle stability, and torque and power characteristics, making it a vital consideration when selecting a camshaft.


Thank you for a moment of your time. Stay safe and save the classics. The Hobbyist





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