Supertech Inconel Exhaust Valve Kit Fits Nissan Skyline R33 RB25DET - Head 30.65mm (+1mm) Length 89mm x12

Made as a one piece forged valve for higher strength and reliability, Supertech use mostly EV8 (21-4N) for Intake and Exhaust valves but there are other alloys that we use along with different heat treatments to manufacture valves for different applications.

Black Nitriding:

This is a hardening treatment that even though it is not widely used as the chrome coating, it has several benefits and is becoming very popular, mainly for European and Japanese applications.
The microhardness is higher than the stainless steel base material, keeping good ductility beneath the hard nitrided layer (microhardness is 800HV minimum). Surface finish is smoother than with chromed stems, having less friction between stem and guide.
Valve seat surface is harder with the nitrided layer, lasting longer with lead free fuels, alcohols, nitro or other "explosive" mixes. Matches any kind of seats (nodular iron seats, steel powder metal seats, hard aluminum-copper seats or beryllium copper seats).