What is cylinder head volume?

The cylinder head volume is the clearance volume in a single cylinder—the space above the piston when it reaches top dead center (TDC) and the valves are closed. This fixed volume, together with the piston’s swept volume, determines the engine’s compression ratio.

Definition and significance

Cylinder head volume (CHV) is usually expressed in cubic centimeters (cc) or milliliters and is a key factor in defining how much air-fuel mixture can be compressed before ignition. It is determined by the combustion chamber geometry, piston crown design, gasket thickness, and related head details. Because it sets the baseline for compression, CHV directly influences efficiency, power, and fuel requirements.

What contributes to CHV

A number of design elements in the engine shape the final clearance volume. The main contributors include:

• Piston crown shape (domed, flat, or dished), which changes the space above the piston at TDC


• Combustion chamber geometry within the cylinder head (hemispherical, pent-roof, dish-shaped, etc.)


• Valve pockets and seat geometry that add or subtract volume around the valves


• Head gasket thickness and the deck surface height relative to the piston top


• Quench/squish zones and other head design features that affect effective clearance

Engineers tune these factors to achieve a target compression ratio and desired combustion characteristics for efficiency and power.

Relation to compression ratio

The compression ratio (CR) is defined as the total cylinder volume at bottom dead center (BDC) divided by the clearance volume at TDC. A standard expression is CR = (V_s + V_c) / V_c, where V_s is the swept (displaced) volume and V_c is the clearance volume. The cylinder head volume is the primary component of V_c.

Practical implications

Smaller CHV raises the compression ratio, which can improve thermal efficiency and power but may increase knock risk and fuel requirements. Larger CHV lowers the compression ratio, making engines more tolerant of lower-octane fuels and boosting reliability in boosted or high-tBoost scenarios.

Illustrative example: consider a single cylinder with a swept volume of 500 cc and a clearance volume of 50 cc. The compression ratio would be (500 + 50) / 50 = 11:1. If the clearance volume increases to 70 cc, CR becomes (570) / 70 ≈ 8.14:1. This shows how CHV directly shifts compression and, consequently, performance characteristics.

Exact numbers vary with engine design, including the number of cylinders, bore and stroke, piston geometry, and gasket selection, but the underlying principle remains constant: CHV is a fixed, design-dependent parameter that helps define how an engine behaves under compression.

Measuring cylinder head volume

CHV is typically measured during engine assembly, rebuilds, or performance tuning. The goal is to determine the volume above the piston at TDC with the valves closed, using precise methods and calibrated equipment. Several approaches exist, including liquid-displacement techniques and manufacturer-provided data.

1. Position the piston at top dead center on the compression stroke and ensure the combustion chamber is sealed from all leakage paths.


2. Fill the chamber with a known liquid (commonly water) using a calibrated container until the space is fully occupied, recording the added volume as the CHV.


3. Correct for any residual volumes in plug ports or gasket cavities if necessary, then report the CHV in cubic centimeters.


4. Cross-check with factory specifications, service manuals, or established measurement procedures to verify accuracy.

Measuring CHV requires precision and appropriate safety precautions. It is best performed by qualified technicians using certified methods and data from the engine’s original or rebuilt specifications.

Impact on design and tuning

Cylinder head volume is a fundamental lever in engine design. By adjusting CHV, engineers can tailor compression ratio to match fuel quality, boosting needs, and emission targets. Common approaches include selecting pistons with specific dish or dome shapes, altering head gasket thickness, and shaping the combustion chamber during head machining.

• Lower CHV to raise compression for improved efficiency and power in naturally aspirated engines


• Increase CHV to lower compression for boosted or high-tolerance fueling scenarios


• Balance CHV with ignition timing, fuel octane, turbocharger design, and cooling strategies to manage knock and heat

In practice, CHV is one element of a holistic design process that aligns combustion chamber geometry with fueling, intake/exhaust tuning, and thermal management to achieve the desired performance envelope.

Summary

cylinder head volume is the fixed clearance volume above the piston at TDC inside the combustion chamber. It works in concert with the swept volume to establish compression ratio, influencing efficiency, power, and fuel requirements. Accurate measurement and thoughtful adjustment of CHV are central to engine design, rebuilds, and performance tuning, always executed with precision and consideration of overall engine system goals.

What is meant by volume of cylinder?

The volume of a cylinder is the amount of space it occupies, calculated by multiplying the area of its circular base by its height. The formula for the volume (Vcap V𝑉) is V=πr2hcap V equals pi r squared h𝑉=𝜋𝑟2ℎ, where 'rr𝑟' is the radius of the base and 'hhℎ' is the height of the cylinder.
 

• Definition: The volume represents the total capacity of the cylinder, measured in cubic units. 
• Calculation:
  • First, find the area of the circular base using the formula for the area of a circle, which is A=πr2cap A equals pi r squared𝐴=𝜋𝑟2. 
  • Then, multiply this base area by the cylinder's height (hhℎ) to get the volume. 
• Formula: The complete formula is V=πr2hcap V equals pi r squared h𝑉=𝜋𝑟2ℎ. 
• Units: The final volume will be in cubic units (e.g., cubic inches, cubic meters, cubic feet). 

What is head volume?

The volume of an adult human head is approximately 0.005 m30.005 m cubed0.005 m3 (5,000 cm35 comma 000 cm cubed5,000 cm3) or around 1,450 cm31 comma 450 cm cubed1,450 cm3. A precise measurement is difficult due to the irregular shape of the head, but it is roughly comparable to the volume of a gallon, as a gallon is about 3,785 cm33 comma 785 cm cubed3,785 cm3. The average adult head volume can range from about 1,2001 comma 2001,200 to 1,500 cm31 comma 500 cm cubed1,500 cm3 and varies based on individual factors. 

• Approximate volume: Approximately 0.005 m30.005 m cubed0.005 m3 or 5,000 cm35 comma 000 cm cubed5,000 cm3. 
• Average adult volume: Around 1,450 cm31 comma 450 cm cubed1,450 cm3. 
• Average adult brain volume: Around 1,450 cm31 comma 450 cm cubed1,450 cm3. 
• Variation: The volume can range from about 1,2001 comma 2001,200 to 1,500 cm31 comma 500 cm cubed1,500 cm3. 
• Measurement: It is challenging to get an exact measurement due to the head's irregular shape, but it can be estimated using formulas that approximate the head as an ellipsoid. 

How to find cylinder head volume?

To measure cylinder head volume, use a burette and a sealing plate to accurately measure the combustion chamber's volume (CC). After installing the spark plug and valves, seal the head and fill the chamber with a liquid like water or alcohol, noting the amount used to fill the chamber completely.
 
This video demonstrates how to measure the combustion chamber volume of a cylinder head: 58sKartFabYouTube · May 25, 2019
Materials needed

• A cylinder head with valves installed
• A sealing plate, often acrylic, with a fill port
• A burette (100ml is common), ideally a glass one
• A burette stand
• A non-reusable spark plug
• A liquid (e.g., water or isopropyl alcohol)
• Grease or Vaseline to create a seal
• A funnel and a beaker for filling the burette 

Step-by-step guide

1. Prepare the cylinder head: Ensure the cylinder head is clean and level. Install the intake and exhaust valves for the specific cylinder you're measuring. 
2. Install the spark plug: Screw the old spark plug into its hole to seal it. 
3. Seal the combustion chamber: Apply a thick bead of grease or Vaseline around the entire perimeter of the combustion chamber on the head's face. Place the acrylic sealing plate over the head, ensuring the fill port is over the chamber. The grease will create a watertight seal. You can use weight to hold the plate down. 
4. Prepare the burette: Fill the burette with the liquid to the 0 or 100 ml mark. Make sure the bottom of the liquid's meniscus is exactly on the zero line and there are no air bubbles. 
5. Fill the combustion chamber: Slowly open the valve on the burette and allow the liquid to flow into the combustion chamber through the fill port. You may need to tilt the head slightly to help any air bubbles escape. 
6. Final measurement: Once the chamber is completely full with no air bubbles, close the burette's valve and read the final volume of the liquid remaining in the burette at the bottom of the meniscus. The difference between your starting volume and final volume is the combustion chamber's volume in cubic centimeters (cc). 

You can also watch this video to learn how to measure cylinder head volume: 59sBriGuyGarageYouTube · Apr 23, 2025

Is it worth fixing a cylinder head?

In many cases, a cracked cylinder head can be repaired rather than replaced, depending on the location and extent of the damage. This is beneficial, as it's generally more expensive to replace a cylinder head than to repair one.