Many mechanics and machinists will remove forged pistons from the box and install them. There is are gains to be made in properly deburring the crowns before installation. This article describes some work performed while building a 2.0l Honda B-Series engine (B18C overbored to 84mm).
The sharp edges from the CnC milling at the factory can be seen clearly above.
These JE pistons have sharp edges around the valve pockets which can remain hotter than the piston crown and encourage detonation. While testing a similar engine before and after dyno sheets were compared and a few extra degrees of timing were possible after deburring the piston crowns. This translated into some torque gains where the engine had been reaching peak cylinder pressure.
The deburring was performed using 1000grit sandpaper (wetsanding paper from a body shop supply store). There are a number of other abrasives, such as 3M scrub pads which also work but we have found this method to give the most consistant and accurate results.
This is the same piston pictured above after the sharp edges have been removed.
It may be a good idea to break the job down into single operations and perform them consecutively on every piston to achieve the most consistant results. Careful comparison is necessary to ensure cylinder to cylinder differences are not introduced. The amount of material removed is generally quite minimal and re-balancing is generally not necessary. The volume of material removed is also small enough that it should not affect the compression ratio.
Here you can see 2 of the pistons compared as they sit in the sleeved block. The piston on the left has been deburred and the one on the right is fresh out of the box.
The heat and flame during combustion does not reach the extreme edges of the piston so it is important not to round the outer edges of the piston. In fact, doing so may contribute to the amount of combustion byproducts being caught by the top piston ring. The 4 pistons for this engine were completed and ready for installation after an hour of work. While this was one of the many tricks employed on this engine it did go home with the customer producing 481whp and 296tq at 8500rpm and 19.5 PSI of boost.