engine room

noun7

1. •
   A compartment on a ship in which the engine machinery is located.
2. •
   The engine compartment of a diesel locomotive.

   • For rigidity, two bulkheads are provided which are welded to the sides and underframe and which separate the cabs from the engine room. — 1958
3. •
   The source of power in a team or other group.
4. •
   (figurative) The midfield.

   • When I look at what is going wrong for Liverpool at the moment, a lot of it stems from the engine room of the team - the midfield. — 2017
5. •
   (figurative) The pair of locks in a team.
6. •
   (figurative) The front row.
7. •
   (figurative) The rhythm section of a steel band.

   • And no steel band would be complete without its rhythm section or engine room, as the percussion section is known. — 2018