For a tank, the engine needs to be powerful, reliable, and also durable, not lightweight. Regardless, the main reason why German tanks broke down wasn't the engine, it was the transmission and final drive. read more
Which is why gun and armor upgrades to existing tanks during WWII were fairly limited, and why really significant increases in gun caliber and armor were generally done with entirely new tank designs with better suspensions, more powerful engines, and sturdier transmissions. read more