CUTAWAY

Boxer engine

Turn the crank and watch the opposed pistons. Both move inward together, then outward together, on separate crankpins.

Boxer engine · 4 cylinders · separate opposed crankpinsBoxer engine: 4 cylinders · separate opposed crankpins. Cutaway shows pistons, connecting rods, crankshaft and cylinder walls.MIT License Copyright (c) 2026 Abhay Kumar Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions: The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software. THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE. MIT License Copyright (c) 2026 Ryan Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions: The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software. THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE. FLAT-FOUR / BOXER CRANK
Piston travel 18% inwardLeft and right travel matchSlow-motion playback

Drag the crank angle or use the arrow keys on the slider. Escape pauses playback.

About this model

This is a generic 4-cylinder boxer layout. Each opposing piston has its own crankpin, 180° from the other. The cylinders are staggered along the shaft so the connecting rods can reach those separate pins.

The separate crankpins make this a boxer; other flat engines can use different crank arrangements. This cutaway removes parts of the heads and liners and omits the valve train, cooling, and lubrication systems.

Piston motion uses a rod-to-crank-radius ratio of 3.5. Dimensions are illustrative and don’t correspond to a specific Subaru or Porsche engine.

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