Reducing the diameter of the valve stem is very effective because it cuts weight on the short side of the rocker arm in the valvetrain. And a fraction of an ounce cut from the rocker pivot to the seat of the valve is more valuable from the rocker pivot to the lifter. To that end, most Nationwide engines are now using titanium valves with 6mm stems. To deal with unleaded race fuel-which will also include 15 percent ethanol next season-engine builders are also going with coated valves. Viccaro says that three coatings that are currently working best are titanium nitride, chromium nitride, and DLC, or "Diamond Like Carbon." These two valves are both coated, but you can only see the DLC coating on the exhaust valve on the left.