according to this article - you are supposed to spend half a day addressing the effects of the sand-casting process:
http://www.hondatuningmagazine.com/t...t/viewall.html
LW: Honda blocks are die cast, whereas Dart blocks are sand-cast. Look at a Honda block and you'll notice how smooth it is relative to an aftermarket version. Internally and externally the Dart block is much rougher, which is why we spend about a half-day going through it to get rid of the coarseness and porosity. This helps oil drain back to the pan faster. We also open up all those passages and polish them for even greater efficiency. Honda heads need lots of oil to ensure valvetrain longevity, so we want to get the oil back to the pan fast to get it circulating.
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