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Automotive tool
Calculate engine displacement, overbore gain, compression ratio, and piston speed
Enter bore, stroke, and cylinder count for the main result, then add optional build details for quick what-if checks.
Calculator inputs
The main result uses (pi / 4) x bore^2 x stroke x cylinders. Overbore, compression ratio, and piston speed sections are optional.
Main geometry
Optional overbore and RPM
Optional compression ratio inputs
Inputs can mix inches and millimeters. Leave optional fields blank if you only want the displacement result.
Solved results
Cubic centimeters for the full engine.
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Bore-to-stroke ratio will appear here.
Enter an overbore amount to compare displacement gain.
Enter chamber, gasket, and deck inputs to estimate compression.
Enter RPM to calculate mean piston speed.
Notes
Use this space for project notes before saving as PDF.
Disclaimer: Use calculations at your own risk. For critical applications, verify results against your governing standards/specifications.
Show the math
1. Normalize the inputs
Enter bore, stroke, and cylinder count to see the normalized values.
2. Find cylinder area
We will calculate cylinder area with (pi / 4) x bore^2.
3. Solve one cylinder
That bore area gets multiplied by stroke to find one cylinder's volume.
4. Multiply by cylinder count
Then we multiply one-cylinder volume by the number of cylinders.
5. Convert to cc and liters
Finally, cubic inches are converted to cubic centimeters and liters.
Optional checks
Overbore, compression ratio, and mean piston speed appear here when their optional inputs are filled in.
Examples and future add-ons
Example combinations
4.000 in x 3.480 in x 8= about349.848 cu in=5.733 L.94 mm x 86 mm x 4= about145.539 cu in=2.385 L.4.030 in x 3.480 in x 8= about355.115 cu in=5.819 L.
Future add-ons
- Bring back a multi-scenario comparison board once the single-calculator flow feels right.
- Add common preset engines as optional quick-fill buttons rather than a full library workspace.
- Add rod ratio and rod-length based reference outputs.
FAQ
Why use pi / 4 in the formula?
The cylinder bore is a circle, so its area is pi x radius^2. Rewriting radius as bore / 2 gives (pi / 4) x bore^2.
Can I mix inches and millimeters?
Yes. Bore, stroke, overbore, gasket bore, gasket thickness, and deck clearance each support inch or millimeter entry.
How should piston volume be entered?
Use a positive number for dish or valve-relief volume that adds to clearance. Use a negative number for a dome that removes clearance volume.
References
- Displacement:
(pi / 4) x bore^2 x stroke x cylinders. - Static compression ratio:
(swept volume + clearance volume) / clearance volume. - Mean piston speed:
2 x stroke x rpm. - Conversion used:
1 cu in = 16.387064 cc, and1000 cc = 1 L.