Valve Coatings
There are 2 types of hi-tech coatings presently available that offers advantages compared to that of convential chrome coating. They are as follows:
Black Nitride - This is a hardening treatment that has several benefits and is becoming very popular. The microhardness (800HV) is higher than the stainless steel base material that keeps good ductility beneath the hard nitrided layer. A surface finish utilizing a Black Nitride coating is smoother than chromed valve stems resutling in less friction between the valve stem and the guide.
A valve's head seat surface is harder with the nitrided layer thus lasting longer with lead free fuels, alcohol and nitro and a Black Nitride valve will match any kind of seats such as nodular iron seats, steel powder metal seats, or beryllium copper seats.
High rpm's engines benefit from Black Nitrided valve, the higher an engine's RPM the greater the power loss due to internal engine friction. The Black Nitride layer reduces the power loss due to less valve-guide friction.
The Black Nitrided layer is adhered to a Valve's base material at a microscopic level, so it can not flake or brake off when a valve bends due to comming in contact with a piston. The Black Nitride coating is applied to the whole valve while the use of a traditional chrome coating is only applied to the stem
Yellow Titanium Nitride (TiN) - Coating also covers the whole valve. This coating is much harder ( 85Rc) than a Molybdenum coating and is a solution to many problems of valve wear on the seat area.
The application of this coating is by PVD (Physical Vapor Deposition) providing the valve with a very hard, frictionless protective coating, and is used by many knowledgeable Race Engine Builders.
This type coating works very well with the Manganese Bronze valve guides and for engines with bucket type tappets there is no need for a valve to have a welded or pressed tip, thus eliminating the risk of breakage.