Piston Compression Height Calculator
Required Piston Compression Height:
0.0000
What is Piston Compression Height?
Compression height (also known as compression distance) is the measurement from the center of the piston pin (wrist pin) to the flat top surface of the piston crown. This measurement is critical for engine builders because it determines where the piston sits in the cylinder at Top Dead Center (TDC).
Getting this measurement correct ensures that your compression ratio is accurate and, more importantly, that your pistons do not strike the cylinder head or valves during operation.
Understanding the Variables
- Block Deck Height: The distance from the center of the crankshaft main bearing bore to the top surface of the engine block deck.
- Connecting Rod Length: The distance between the center of the big-end bore and the center of the small-end bore.
- Crankshaft Stroke: The total distance the piston travels from TDC to BDC. We divide this by 2 (the crank throw radius) for the formula.
- Deck Clearance: How far below the deck the piston sits at TDC. A positive number means the piston is "in the hole."
Example Calculation
Imagine you are building a Small Block Chevy 350. Your block has been milled to a 9.000″ deck height. You are using 5.700″ rods and a standard 3.480″ stroke crankshaft. You want the piston to sit 0.015″ below the deck.
1. Half the stroke: 3.480 / 2 = 1.740″
2. Sum of components: 5.700 + 1.740 + 0.015 = 7.455″
3. Subtract from Deck: 9.000 – 7.455 = 1.545″
Your required piston compression height would be 1.545 inches.
Why Precision Matters
In high-performance engines, even 0.005″ can significantly impact the quench area and static compression ratio. If the compression height is too tall, the piston will protrude from the block, potentially hitting the head. If it is too short, you will lose compression and efficiency due to a poor quench effect.