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Why are diesel engines generally heavier and more expensive than gasoline engines of the same horsepower?

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diesel engine and precombustion chamber — diesel engine Diesel engine equipped with a precombustion chamber.

Diesel engines are generally heavier and more expensive than gasoline engines of the same horsepower primarily due to their structural requirements for handling high-pressure combustion.

Because diesel engines operate as compression-ignition systems rather than using a spark-ignition system, they require significantly higher compression ratios—typically ranging from 14:1 to 22:1—to heat the air sufficiently for fuel auto-ignition. To withstand the intense mechanical stresses and high pressures generated by these ratios, the engine components must be built with greater structural strength and durability, which increases both the overall weight and the manufacturing costs.12

Despite these factors, diesel engines are often preferred for certain applications because they offer a longer operational life and lower fuel costs per horsepower-hour compared to gasoline engines.2