What is the Difference Between a Four-Cylinder and a Three-Cylinder Engine?
3 Answers
The differences between a four-cylinder and a three-cylinder engine are as follows: Structural design: The three-cylinder engine has a simple structure, small size, light weight, and is easy to arrange. The four-cylinder engine has a relatively complex structure and one more cylinder. In terms of structural design, the three-cylinder engine has one less cylinder than the four-cylinder engine, and the corresponding camshaft has fewer attachments. Fuel consumption: The three-cylinder engine has less pumping loss. With one less cylinder, the three-cylinder engine theoretically has less resistance, and the resistance loss caused by mechanical friction is smaller than that of the four-cylinder engine. Fuel consumption will be slightly lower. Torque: The three-cylinder engine has greater low-speed torque output but smaller high-speed torque, with more significant power attenuation. The three-cylinder engine has a smaller bore and a longer piston stroke. This design is beneficial for the engine's low-speed torque. Therefore, the low torque of the three-cylinder engine is better than that of the four-cylinder engine. However, the corresponding power attenuation and responsiveness will change in the high-speed range. Differences.
I've owned a three-cylinder car and also driven four-cylinder ones. The biggest differences are vibration and noise. With one less cylinder, the three-cylinder engine has uneven power distribution during operation, causing noticeable buzzing vibrations in the steering wheel at idle and low speeds, especially when the AC is turned up high. At highway speeds when the engine RPM increases, it becomes less noticeable, but the engine sound during hard acceleration sounds rougher. Four-cylinder engines have two cylinders on each side that cancel out vibrations, making the cabin noticeably quieter and more stable. However, newer three-cylinder models now come with balance shafts and hydraulic engine mounts, which are much better than when I bought my car years ago. In terms of fuel consumption, three-cylinder engines have an advantage due to their smaller displacement and lighter weight, saving about half a liter per 100km in city driving. If comfort is a top priority, I'd still recommend choosing a four-cylinder car.
From a mechanical perspective, the differences between these two engine types are quite fascinating. A three-cylinder engine fires its three cylinders in sequence, with each ignition occurring at 240 degrees of crankshaft rotation, resulting in longer intervals between power pulses compared to a four-cylinder engine's tighter 180-degree intervals that deliver smoother power delivery. By eliminating one cylinder, the three-cylinder design sheds over ten kilograms in weight and achieves a more compact layout, freeing up additional space in the front compartment for batteries and electric motors. However, the missing cylinder creates rotational imbalance, requiring counterweights or balance shafts to mitigate vibrations—a more technically challenging solution than the four-cylinder's inherently balanced symmetrical design that delivers inherently smoother power output. Additionally, at high RPMs each cylinder in a three-cylinder engine bears greater individual load, which theoretically could impact longevity, though modern material advancements have largely addressed this concern.
