From http://world.honda.com/NSX/technology/t5.html
Blueprinting and balancing of the crankcase assembly for engine feel and response that will set your heart pounding
The engine employs the same kind of high precision dynamic balanced clutch cover, fly wheel, and pulley assembly as is used in racing engines. Highly qualified veteran technicians check each assembly with a balancer, pruning away tiny specks of metal with their high precision drill. Rotating weight tolerance is reduced to below 1/10 that of the base NSX, to correspond to the same exacting standards used in racing.
To obtain the maximum effect of this high-precision balancing, weight tolerances of the piston and connecting rod pairs are controlled to within about half that of the base model, just as in the original NSX-R. Crankcase-side and engine block-side main journal diameters are measured, and those having the same bearing metal thickness are combined to increase metal clearance precision and reduce friction. The adoption of these and other time-consuming methods normally unheard of in mass-production imbue the New NSX-R's engine with breathtaking response and feel.