INTAKE & EXHAUST VALVE THERMAL COATINGS

Distortion of the intake and exhaust seats is just one of many problems caused by heat. Because intake valves don't have to pass copious quantities of high temperature gases, it is often assumed they run relatively cool. But remember, the intake valve has a larger area than the exhaust valve and is subjected to virtually the same combustion temperatures. It doesn't get hot because it conveys much of its contained heat into the last place it is needed - the intake charge. As a result, charge density drops. Any time the conduction of heat to the intake charge by means of intake valve can be reduced, an increase in power will be seen. Since the intake valve presents the hottest surface in the entire induction system, it makes sense to focus some attention on it. Applying thermal coatings to the combustion chamber safe of the intake valve can add torque to the engines output through rpm range. It's only a small amount, but every little bit adds up. A fair estimate would be one, at most two percent gain.

Rather than worry about dumping heat through the seats or stem, a better approach is to look for a way to prevent heat from getting into the valve in the first place. This is yet another instance where thermal barrier coating can pay off. By coating the face of the valve, as suggested for the inlet, and the underhead area, you ensure that the valve becomes substantially insulated from the hot exhaust while retaining an unimpaired ability to dump heat through the stem and seat. The net result here is that the valve temperature can be significantly reduced. A 100 degree Fahrenheit drop in temperature on a 21-4N steel exhaust valve can make a difference in the tensile strength of 20,000 lb/sq in letter.

[BACK]