Caterpillar 621K vs Caterpillar 637K

	Caterpillar Caterpillar 621K	Caterpillar Caterpillar 637K
Operating weight	—	—
Engine power	—	—
Heaped capacity	≈18 m³ (24 yd³)	≈26 m³ (34 yd³)
Rated load	≈22,000 kg (48,500 lb)	—
Engine	Cat C13	—
Configuration	Single engine, open bowl	Twin engine, push-pull capable
Strengths	+ Versatile mid-size capacity + Lower cost than twin-engine models + Cat dealer support	+ Excellent traction + Push-pull loading
Watch-outs	− Needs a push dozer to load fully	− High running cost
	Full 621K review	Full 637K review

Specifications are typical figures for standard configurations and may be measured differently by each manufacturer (for example net vs gross power). Always confirm with the manufacturer or dealer. Build another comparison.