The cylinder heads are machined from aluminum billets. As such, they, too, lack water jackets and rely entirely on the incoming air/fuel mixture and lubricating oil for their cooling. The original Chrysler design of two large valves per cylinder is used. The intake valve is made from solid titanium and the exhaust from solid Nimonic 80A or similar. Seats are of ductile iron. Beryllium-copper has been tried but its use is limited due to its toxicity. Valve sizes are around for the intake and for the exhaust. In the ports there are integral tubes for the push rods. The heads are sealed to the block by copper gaskets and stainless steel o-rings. Securing the heads to the block is done with aircraft-rated steel studs and stud nuts.