How well it works
How Motor Forge works
Engine: the size (displacement) comes from the bore, stroke and number of cylinders. Torque is the size times a typical cylinder pressure (BMEP) for that kind of engine — about 12–13 bar for a petrol engine without a turbo, and roughly double with boost. Higher compression burns the fuel more efficiently. The cam profile shapes where the engine breathes best, and friction grows with piston speed. Power is torque × revs.
Performance: a simulation steps through a full-throttle run a hundredth of a second at a time. At each moment it picks the best gear, works out the pushing force at the wheels, limits it by tyre grip (with weight moving backwards as you accelerate, and wheelies on a motorcycle), and subtracts air drag (½·ρ·Cd·A·v²) and rolling resistance. Braking is limited by grip, and on a motorcycle by the rear wheel lifting. Fuel use comes from the power needed at a steady 100 km/h and how efficient the engine is at that light load.
These are estimates for learning and comparing designs, usually within 10–20% of real vehicles. Real cars and motorcycles also need crash safety, cooling, emissions and road approval.