Hi Ken/All,

I teach in an engineering dept. here, and supervised a project that
involved ceramic coating on piston, valves and head.  Exhaust valve
coating 'wore' off during use, others showed no signs of wear.  Silicon
nitride drops heat conduction coefficient to 1/6th of that of steel, and
boosts combustion chamber temps hence efficiency. Better coating is
zirconia type, drops to <1/25th. 

Coating was applied by Adiabatics Inc. of Columbus, Indiana, coating
LT-450, a ceramic metal, cermet, type (of 70% cubic zirconia)

  There are reported power gains( GM 2.5l engine) of 18% at low-mid
RPMs, 10% at mid-upper, but also of fall-off by 8% at higher RPMs due to
lubrication problems.  The engine we did, a Briggs and Stratton 2HP
destined for Shells SuperMileage Competition, showed 7% increase in
torque that dropped off to 1.3% at higher RPMs.  Best part was the 15%
reduction in fuel consumption at mid RPM.  Bottom line was fairly
consistent 2% increase in combustion efficiency.

Can't remember pricing at all, rest I'm reading from the report. 
Remember, YMMV, and it will!  :)   Since Todd Francis has posted about
having badly pitted heads fixed up with ceramics, it is a small step
further to get the heads completely sprayed.  Maybe a nice option for
someones next wasserpisser rebuild.  bye, Tim