The SpaceX Merlin 1D engine, the more powerful, more robust and less expensive
follow on to the operational 1C, has been certified for flight.

This is the family, an interesting thing about the Heavy is the plan to have the strap-ons share fuel with the core, consequently when they separate the core is still fully fueled, a big performance increase.

The engines have been run far harder than standard rating regimes require, 1) to solidify their ‘man rating’ for future crew lofting flights, 2) because SpaceX wants to reuse them, 3) because SpaceX wants top line insurance rates for their customers even while brining new approaches to the party.

Rocket engines, so ugly you just know they’re powerful!