piston

An engine dyno simulator in C++17. Four-stroke spark-ignition
engines and basic compression-ignition, from the command line,
with an optional ImGui front end.

Status    Early alpha (v0.1.0-alpha), as of 2026-09-30. It is not
          validated for engineering use. Do not rely on its numbers.

Accuracy  22 engines in the validation set, wide open throttle, SAE
          J1349 corrected. Mean absolute error across the set is 8.2
          percent on peak power and 5.0 percent on torque. Worst
          peak-power cases: Ford Flathead V8 +30.2, 2JZ-GTE -16.9,
          Honda F20C +15.5 percent. Only 3 engines are compared
          against a measured dyno curve; the rest use spec-sheet
          peaks. There is no blind predict-then-dyno test yet, and
          part throttle is not checked against anything.

Models    Otto and detailed cycles (Wiebe combustion, Woschni heat
          transfer), slider-crank with Chen-Flynn friction, a 1D
          intake with cam phasing and VTEC lobes, knock retard,
          residual gas, turbo power balance. Two-zone combustion,
          the parts database and forced induction are partial.

Build     CMake, Ninja and MinGW-w64 GCC 13. No installer yet, and
          release binaries will be unsigned.

Usage     piston simulate -c engine.json -o out.csv
          piston report -c engine.json -o report.html
          piston --help

License   Source is proprietary. Release binaries are free to use
          under an EULA.