A smaller diameter crank pulley is a requirement on our NC swap, but also a recommended upgrade for all other swaps. This is the pulley from the 2002-2006 RSX Type S.

A smaller crank pulley under drives the accessories and increases alternator life. And for the NC, it keeps the NC power steering pump from overspinning and cavitating. 

For an even more robust option, an ATI damper or Fluidampr can also be used, as they are both K20 sized.