What are the core parameters of the engine: displacement, power, torque, and power per liter?

Displacement is the Basis

First of all, the displacement of the engine, which is generally measured in L, represents the size of the sum of the cylinder volumes of all the cylinders of the engine. The larger the cylinder volume, the more mixed gas can be inhaled at one time, and the combustion work can generate more energy. Displacement is the basis of all power parameters of the engine. If you want to increase the engine displacement, you can either expand the volume of a single cylinder or increase the number of cylinders. However, with the continuous tightening of emission policies, large-displacement engines have become less and less. Most OEMs still hope to increase the output power of the engine while ensuring that the displacement remains unchanged, so there are various technologies such as turbocharging, variable valve timing, dual injection, and dual cycle.

Power and Torque

Power is a physical quantity that describes the speed of work. The power of the engine is the amount of work done by the engine per unit time. Maximum power refers to the peak power of the engine under extreme conditions. Four-stroke engines generally use piston reciprocating motion to do work. After the piston does work, it will transfer energy to the crankshaft to form a torque. This torque is the torque of the engine.

The Relationship between Power and Torque

To understand the relationship between power and torque, we can imagine torque as the amount of oil and gas inhaled by the cylinder in one breath. This intake volume will gradually increase with the increase of the throttle opening and the increase of speed. However, torque cannot increase all the time. When the throttle is opened and the speed reaches a certain value, it can no longer increase, which is what we often call the maximum torque. Power = speed * torque, which can be imagined as the amount of oil and gas that the engine can inhale per unit time. Therefore, when the engine speed gradually increases and slowly reaches the maximum torque, the intake volume per unit time is also gradually increasing. When the speed exceeds the tolerance range of the maximum torque, although the torque is decreasing, the increase in speed can still increase the intake volume.

Engine Power Per Liter

The engine power per liter means that the effective power output per unit engine displacement is actually power/displacement, which is the power that can be brought by each 1L cylinder. Liter power can well reflect the advancement of an engine. Without good technology, it is not difficult to increase horsepower by simply stacking cylinders, but when the displacement is fixed, doing everything possible to improve the work efficiency of each cylinder is hard power.

In general, there is a strong correlation between the engine's displacement, power, torque, and liter power. Displacement and power are the basis, torque is the intuitive expression, and liter power is a technical indicator.