Extreme Engine Tech: Building a BMW S52 – Part 2: The Cylinder Head
If the engine as a whole is the heart of a car the cylinder head would be all the supporting parts that make the heart pump. Without the opening and closing of certain valves the heart wouldn't be able to get blood to flow into the atriums and out the ventricles. Just like the heart, a cylinder head has multiple valves, that need to open and close at specific times, to get air in to, and exhaust out of, the combustion chambers to keep the engine pumping.
In order to keep Project E36 323is’ high compression bottom end from cardiac arrest we need to make sure the cylinder head matched the needs of the bottom end. If you remember from part 1 of our S52 build the only cylinder head parts we had from our original purchase of a used S52 were the cams and cam trays, due to a crack in the original S52 head we returned it with the valvetrain to the original owner, this quite literally left a few holes to plug. With the help of Supertech, Pelican Parts and Pure Performance we’ve managed to build a head with a lightweight valvetrain while maintaining OEM reliability.
The first step into building our head was to plug the holes, specifically the 24 holes left vacant from the lack of valves, for this we turned to Supertech.
For the exhaust side of things we went with Supertech Inconel valves. Supertech exhaust valves are made of heat resisting one piece inconel forgings. Many valves use two piece spin welded construction. Two piece valves tend to loose their heads under pressure so a once piece valve is the only way to go for a performance application.
The benefit of Inconel exhaust valves is their resistance to high temperatures. Inconel is an aerospace alloy developed specifically for operation in extreme high temperatures and pressures. Inconel is an alloy primarily composed of nickel and chromium. The exhaust valves are not cooled by the intake charge on every cycle like the intake valves are. High performance engines run hotter on the exhaust side as well so inconel is the wise choice for materials here.
For the best heat transfer and strength at high temperatures the exhaust valve stem is only minimally reduced near the valve head. The valve heads have a tulip shape for best exhaust flow.
For our intake side we chose Supertech standard Black Nitride valves. The intake valves are made from stainless steel. Like the exhaust valves, the intake valves are made from one piece forgings. it is common for valves to have the shafts spin welded to the heads which is inherently weak. Forging ensures proper grain flow and a homogenous super strong valve.