Enter your engine's Bore Diameter and Stroke Length into the Stroke/Bore Ratio Calculator, choose your Unit System, and instantly find your Stroke/Bore Ratio, Engine Type (undersquare, square, or oversquare), and detailed Engine Characteristics that explain how your cylinder geometry shapes power delivery and rev range.
Stroke/Bore Ratio
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Engine Type
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Bore/Stroke Ratio
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Engine Characteristics
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Stroke-to-bore ratio is the relationship between the piston stroke length and cylinder bore diameter. This ratio affects engine performance characteristics like torque delivery, RPM capability, and combustion efficiency.
A high stroke-to-bore ratio (typically over 1.0) indicates a long-stroke engine design. These engines typically produce more torque at lower RPMs and are often more fuel efficient but may have lower maximum RPM capabilities.
A low stroke-to-bore ratio (under 1.0) indicates an oversquare or short-stroke engine. These engines can typically rev higher, produce more horsepower at high RPMs, and have better breathing characteristics for performance applications.
There's no universal ideal ratio as it depends on the engine's intended use. Performance engines often use ratios of 0.8-0.95, while torque-focused engines may use ratios of 1.0-1.2 or higher.
Both bore and stroke contribute to engine displacement. A larger bore increases displacement more efficiently than a longer stroke, which is why high-performance engines often favor larger bores with shorter strokes.
Yes, but it requires significant engine modifications. You can change the stroke with a different crankshaft or bore the cylinders larger, though both modifications require careful consideration of other engine components.
Oversquare engines have a bore diameter larger than the stroke length (ratio < 1.0), while undersquare engines have a stroke length greater than the bore diameter (ratio > 1.0). Square engines have equal bore and stroke (ratio = 1.0).