EngineLabs: What are the pros and cons of using tool steel for retainers?
Urritia: We started our tool steel retainer program three years ago and have had nothing but great success because of two main points: We are designing the tool steel retainers to be within 3-4 grams of weight difference compared to titanium retainers; and the tool retainers also last five times longer than the titanium retainers in most applications. If everything is working properly in the valvetrain, you can reuse them with newer valve springs.
Urritia: Pro Stock valvetrain has been always a challenge with controlling harmonics on a valve spring or controlling deflection on the valves. We have been able to continue to redesigned the valve and lighten up the weight for increase control. To compete in Pro Stock today you must run a hollow-stem titanium valve on the intake side. This allows you to address the large issue of deflection and keep the valvetrain harmonics controlled.
EngineLabs: Please explain the benefits of sodium-filled valves and what are their best applications? Also, any downsides to using sodium-filled valves?
Urritia: Sodium-based valves were manufactured in the ’60s when then aerospace industry had piston-driven engines and needed to find a way to cool down the exhaust valves. They were eventually manufactured for the OE automotive industry and are still used today. They work well in controlled environments where the temperature change is not drastic. If you installed sodium-filled valves in an racing engine, you will find issues with the sodium not working properly to cool the bottom area of the stem of the valve. The sodium would stop working and create a possible failure where the valve is now hollow in that area.
EngineLabs: What new finishing procedures and coatings should racers be aware of, and what are their benefits?
Urritia: This all depends on the material of each valve. If we are talking about stainless-steel exotic alloys, we still use avionics-quality hard chrome stems. Some engine builders will apply different coating on the seat and profile of the stainless steel valves, but with our valves it is not needed. On titanium valves we use CrN (Chrome Nitride) through the entire valve. We have tested several coatings that are available in the market and we feel that the way this type of coating applies on our titanium material is best.
EngineLabs: Titanium seems to be on everyone’s wish list, but what are the best applications for titanium valves?
Urritia: Titanium has been placed in many industries as a name brand. The automotive manufactures have started placing titanium valves in OEM engines. The OEM manufactures have found particular coatings that apply themselves well and help through the stress factor of a factory engine. One coating is CrN, like I mention in the prior question this is a great coating when applied thicker throughout the valve for OE engines. In the performance and racing industry we see environments that are very drastic in each engine build. We do not recommend to engine builders to install titanium valves if the engine is a gas powered supercharged or turbocharged engine, due to the excessive amount of heat fluctuation. We do recommend titanium valves when the overall weight of the valve train becomes unstable due to the excessive amount of rpm and camshaft lifts.