Stroke ratio
mechanics term
Stroke ratio, today often defined as bore/stroke ratio, is a term to describe the ratio between cylinder bore diameter and piston stroke length in a reciprocating piston engine. This can be used for either an internal combustion engine, where the fuel is burned within the cylinders of the engine, or external combustion engine, such as a steam engine, where the combustion of the fuel takes place outside the working cylinders of the engine.
Conventions
The usual way to describe the stroke ratio of a piston engine‘s cylinders is its bore/stroke ratio. The diameter of the cylinder bore is divided by the length of the piston stroke to give the ratio.
Stroke/bore ratio is an less popular expression, dating from the early days of internal combustion engine development.
Square, oversquare and undersquare engines
The following terms are used to label bore/stroke ratio:
Square engine
A square engine has equal bore and stroke dimensions, giving a bore/stroke value of exactly 1:1.
Square engine examples
1953 – Ferrari 250 Europa had Lampredi V12 with 68.0 mm × 68.0 mm (2.7 in × 2.7 in) bore and stroke.
1967 – FIAT 125, 124Sport engine 125A000, 125B000, 125BC000, 1608 ccm, DOHC, 80.0 mm × 80.0 mm (3.15 in × 3.15 in) bore and stroke.
1970 – Ford 400 had a 101.6 mm × 101.6 mm (4.00 in × 4.00 in) bore and stroke.
1973 – Kawasaki Z1 and KZ(Z)900 had a 66.0 mm × 66.0 mm (2.60 in × 2.60 in) bore and stroke.
“Stroke ratio” enters the record as mechanics term. Crown Archives preserves that source wording while asking what Stroke, ratio and mechanics can confirm, complicate or overturn.
Why this record matters
“Stroke ratio” is worth following because a concise public description often conceals a longer documentary argument. Here, Stroke, ratio and mechanics provides the most credible route into that argument.
Named sources, stable identifiers and responsible institutions provide the strongest route from overview to verifiable evidence. The source revision retrieved here is dated Sep 19, 2026. The linked authority identifier is Q844463. None of the 0 selected statements returned an explicit reference. The first chronological checks are 1953, 1967, 1608 and 1970.
A concise general-reference account can conceal disagreements about scope, terminology or the weight assigned to individual sources. The lead is largely declarative, so disagreement and counter-evidence require a deliberate search beyond the opening account. Authority statements aid reconciliation but still require their own references, qualifiers and ranks to be checked.
How to read it
Use the entry as an orientation point, then follow its citations and revision history. Names, dates and institutional relationships should be checked against the original record.
- Subject orientation
- Search vocabulary
- Locating named sources
The closest primary source, responsible institution and strongest cited specialist reference.
Three-step research path
- Establish the record: confirm the title “Stroke ratio”, its source revision and the description used here.
- Expand the search: follow Stroke ratio primary sources, Stroke ratio archive and Stroke research across catalogues and specialist indexes.
- Test the account: compare the strongest cited source with the responsible institution’s current record and note any disagreement.
Questions for further research
- Which source most directly establishes the central claim about “Stroke ratio”?
- Which cited source is closest to the event, object or claim?
- Which institution is responsible for the underlying evidence?
Search terms from this dossier
This entry incorporates text from “Stroke ratio” on English Wikipedia. Contributors are listed in the page history. Text is available under the Creative Commons Attribution-ShareAlike 4.0 License. Selected authority identifiers and statements are retrieved from Wikidata under CC0; their references and qualifiers remain part of the verification path.