Cam Timing Calculator

Calculate LSA, Duration, and Overlap for your engine’s camshaft.

Calculation Results:

Formulas Used:
Intake Duration = Intake Open + 180 + Intake Close
Exhaust Duration = Exhaust Open + 180 + Exhaust Close
Overlap = Intake Open + Exhaust Close (all relative to TDC/BDC as appropriate)
Intake Centerline = (Intake Duration / 2) – Intake Open (from TDC)
Exhaust Centerline = (Exhaust Duration / 2) – Exhaust Close (from TDC)
LSA = (Intake Centerline + Exhaust Centerline) / 2

Comparison of Intake Duration, Exhaust Duration, and Overlap.

What is a Cam Timing Calculator?

A cam timing calculator is a tool used by engine builders, tuners, and enthusiasts to determine key characteristics of a camshaft’s timing based on the valve opening and closing events. It helps calculate the intake and exhaust duration, valve overlap, Lobe Separation Angle (LSA), and intake/exhaust centerlines. Understanding these parameters is crucial for predicting and tuning an engine’s performance characteristics, such as its power band, idle quality, and fuel efficiency. The cam timing calculator takes the guesswork out of camshaft selection and setup.

Anyone working on internal combustion engines, from professional race engine builders to hobbyists modifying their car or motorcycle, can benefit from using a cam timing calculator. It allows for quick comparisons between different camshaft specifications or the effect of advancing or retarding cam timing.

Common misconceptions are that LSA alone defines a cam’s behavior, or that more duration always means more power. A cam timing calculator helps show the interplay between duration, LSA, and overlap to give a more complete picture.

Cam Timing Calculator Formula and Mathematical Explanation

The calculations performed by the cam timing calculator are based on the rotational position of the crankshaft (in degrees) when the intake and exhaust valves open and close.

1. Converting to Degrees from TDC/BDC: First, we convert the opening and closing events to degrees relative to Top Dead Center (TDC) and Bottom Dead Center (BDC), considering whether they happen Before (B) or After (A). For example, Intake Open BTDC is positive, ATDC is negative relative to TDC for duration start.
2. Duration Calculation:
   • Intake Duration = (Intake Open relative to TDC) + 180° + (Intake Close relative to BDC)
   • Exhaust Duration = (Exhaust Open relative to BDC) + 180° + (Exhaust Close relative to TDC)
3. Overlap Calculation: Valve Overlap occurs when both intake and exhaust valves are open simultaneously around TDC at the end of the exhaust stroke and beginning of the intake stroke. Overlap = (Intake Open relative to TDC) + (Exhaust Close relative to TDC) (using absolute degrees before/after TDC).
4. Centerline Calculation:
   • Intake Centerline (ICL) = (Intake Duration / 2) – (Intake Open relative to TDC). This is typically expressed as degrees ATDC.
   • Exhaust Centerline (ECL) = (Exhaust Duration / 2) – (Exhaust Close relative to TDC). This is typically expressed as degrees BTDC.
5. Lobe Separation Angle (LSA) Calculation: LSA is the angle in camshaft degrees between the peak lift of the intake lobe and the peak lift of the exhaust lobe. LSA = (ICL + ECL) / 2.

Variables in Cam Timing Calculations

Variable	Meaning	Unit	Typical Range
Intake/Exhaust Open/Close	Crankshaft angle when the valve starts to open or fully closes	Degrees (°)	0 – 90
Reference (BTDC, ATDC, BBDC, ABDC)	Reference point for the angle (Before/After Top/Bottom Dead Center)	N/A	N/A
Intake/Exhaust Duration	Total angle the valve is open	Degrees (°)	180 – 320+
Overlap	Angle both valves are open	Degrees (°)	0 – 100+
ICL / ECL	Intake / Exhaust Centerline – point of max lift relative to TDC	Degrees (°)	90 – 130
LSA	Lobe Separation Angle	Degrees (°)	100 – 120+

Practical Examples (Real-World Use Cases)

Example 1: Street Performance Cam

An engine builder is choosing a cam for a street performance car. They are considering a cam with the following specs:

• Intake Open: 18° BTDC
• Intake Close: 42° ABDC
• Exhaust Open: 50° BBDC
• Exhaust Close: 14° ATDC

Using the cam timing calculator:

• Intake Duration = 18 + 180 + 42 = 240°
• Exhaust Duration = 50 + 180 + 14 = 244°
• Overlap = 18 + 14 = 32°
• ICL = (240 / 2) – 18 = 120 – 18 = 102° ATDC
• ECL = (244 / 2) – 14 = 122 – 14 = 108° BTDC
• LSA = (102 + 108) / 2 = 105°

This cam has moderate duration and overlap with a relatively tight LSA, suggesting good mid-range power with a noticeable idle.

Example 2: Mild RV/Towing Cam

A user wants a cam for good low-end torque for towing:

• Intake Open: 10° BTDC
• Intake Close: 30° ABDC
• Exhaust Open: 40° BBDC
• Exhaust Close: 5° ATDC

Using the cam timing calculator:

• Intake Duration = 10 + 180 + 30 = 220°
• Exhaust Duration = 40 + 180 + 5 = 225°
• Overlap = 10 + 5 = 15°
• ICL = (220 / 2) – 10 = 110 – 10 = 100° ATDC
• ECL = (225 / 2) – 5 = 112.5 – 5 = 107.5° BTDC
• LSA = (100 + 107.5) / 2 = 103.75°

Shorter duration, less overlap, and a slightly wider LSA compared to Example 1 would generally favor lower RPM torque and smoother idle, suitable for towing.

How to Use This Cam Timing Calculator

1. Enter Valve Events: Input the degrees for when the intake and exhaust valves open and close.
2. Select References: For each event, select the correct reference point: BTDC (Before Top Dead Center), ATDC (After Top Dead Center), BBDC (Before Bottom Dead Center), or ABDC (After Bottom Dead Center).
3. Calculate: The calculator will automatically update the results as you input the values. You can also click the “Calculate” button.
4. Review Results: The calculator displays Intake Duration, Exhaust Duration, Valve Overlap, Intake Centerline, Exhaust Centerline, and the primary result, Lobe Separation Angle (LSA). The chart visualizes durations and overlap.
5. Reset: Click “Reset” to return to default values.
6. Copy: Click “Copy Results” to copy the inputs and outputs to your clipboard.

The results from the cam timing calculator help you understand the camshaft’s characteristics. A tighter LSA (e.g., 104-108°) with more overlap generally moves the power band higher and results in a rougher idle. A wider LSA (e.g., 110-114°) with less overlap typically provides a smoother idle, better vacuum, and a broader power band, but may sacrifice some peak power. See our guide on understanding camshafts for more info.

Key Factors That Affect Cam Timing Calculator Results

1. Intake/Exhaust Opening/Closing Points: These are the fundamental inputs that directly determine all other calculated values. Changing any of these will alter duration, overlap, centerlines, and LSA.
2. Advertised Duration vs. Duration at 0.050″ Lift: Cam specs are often given at different lift points (e.g., advertised vs. @0.050″). The cam timing calculator uses the opening/closing events, which are usually associated with advertised duration or a very small lift (like 0.006″). Using events at 0.050″ will give different, shorter duration numbers.
3. Lobe Separation Angle (LSA): While calculated here, if you are working backward from a known LSA and centerlines, it dictates the relationship between intake and exhaust events. Tighter LSA increases overlap for the same duration.
4. Cam Advance/Retard: Physically advancing or retarding the camshaft (relative to the crankshaft) changes the intake and exhaust centerlines equally, shifting the power band, but does not change LSA or duration. Our basic cam timing calculator assumes the cam is installed “straight up”, but advanced/retarded timing can be inferred by adjusting centerlines or event timing. Learn more about how valve timing affects performance.
5. Engine Application: The desired cam timing specs vary greatly depending on whether the engine is for street use, racing, towing, or fuel economy. Street engines generally use wider LSA and less overlap than race engines.
6. Engine Displacement and Compression Ratio: Larger displacement or higher compression engines can often tolerate more duration and overlap than smaller or lower compression ones. You might also want to check our compression ratio calculator.
7. Rocker Arm Ratio: While not directly in these calculations, rocker arm ratio affects valve lift and effective duration at higher lifts, which influences performance.

Frequently Asked Questions (FAQ)

What is Lobe Separation Angle (LSA)?

LSA is the angle in camshaft degrees between the maximum lift points of the intake and exhaust lobes. It affects the amount of valve overlap and the engine’s power band and idle characteristics.

What is Valve Overlap?

Valve overlap is the period, measured in crankshaft degrees, when both the intake and exhaust valves are open simultaneously. It occurs around TDC at the end of the exhaust stroke and the beginning of the intake stroke.

How does LSA affect engine performance?

A tighter LSA (smaller number) generally increases overlap, can lead to a rougher idle, lower vacuum, and moves the power band to higher RPMs. A wider LSA (larger number) typically reduces overlap, gives a smoother idle, better vacuum, and a broader power band.

How does duration affect engine performance?

Longer duration keeps the valves open longer, which can allow more air/fuel mixture to enter and exhaust to exit at higher RPMs, potentially increasing high-RPM power but possibly sacrificing low-RPM torque and idle quality.

What is the difference between advertised duration and duration at 0.050″ lift?

Advertised duration is measured from a very small amount of lift (e.g., 0.006″), while duration at 0.050″ is measured from 0.050″ of valve lift on both the opening and closing sides of the lobe. The 0.050″ number is more standardized for comparing cams with different ramp rates.

How do I use this cam timing calculator with 0.050″ specs?

You would input the opening and closing events specified at 0.050″ lift to get duration and LSA figures based on that measurement point. The results will be different from those calculated using advertised specs.

What is a good LSA for a street car?

For a street-driven car, an LSA between 108 and 114 degrees is common, depending on the engine and desired performance. Wider LSAs (112-114+) often give better drivability and vacuum.

Can I calculate cam advance with this cam timing calculator?

This calculator determines the LSA based on the events as entered. If you know the LSA and want to see the effect of advance, you would typically adjust the Intake Centerline (advancing the cam makes the ICL number smaller ATDC).

Related Tools and Internal Resources

• Engine Displacement Calculator: Calculate your engine’s displacement based on bore and stroke.
• Compression Ratio Calculator: Determine the static compression ratio of your engine.
• Understanding Camshafts: A guide to camshaft terminology and effects.
• How Valve Timing Affects Performance: Learn about the impact of cam timing on engine output.
• RPM Calculator: Calculate engine RPM based on speed, gear ratio, and tire size.
• HP to kW Converter: Convert horsepower to kilowatts and vice-versa.