Finally, once broken in, the engine receives a final balance. This is done with the engine fully assembled and filled with oil and at operating temperature. Balance is measured at each end of the crankshaft, and perfect balance is achieved through the use of specially weighted flywheel bolts.

This new generation Acura NSX engine is an amazing piece of engineering, making 143 horsepower-per-liter out of the gate, with the ability to hold its own in an international racing class like GT3, while also handling the day-to-day rigors of rush-hour traffic in the middle of summer. This engine truly is an engineering marvel.
The final engine balance is done with the engine fully assembled and broken in, through the use of these weighted flywheel bolts.

Article Sources

Acura
https://www.acura.com/