Use unleaded fuel with confidence, and reduce the weight of your engine while increasing its efficiency and performance with one of these aluminum alloy cylinder heads. (The 6-cylinder head weighs approximately 51 lbs. less than the original head it replaces!) While these heads look like the originals externally, thin weak areas of the originals have been beefed up for long-lasting reliability. Ports and combustion chambers are polished and balanced, and special 'figure eight' stainless steel valve seat inserts are used to give these heads distinct advantages over the stock cast iron heads. Valve guides are installed, and heads are supplied with valves, springs and retainers, studs, etc. We strongly suggest using the ARP Performance Fastener Set # 328-876 for 6-cylinder applications.