As with all parts of a hot rod or specially constructed muscle car, the oil used as the life blood of the engine has to be custom fit to provide the best performance. A special additive known as zinc dialkyldithiophosphate (ZDDP) is used as an anti-wear agent and is integral to the proper functioning of these flat tappet engines. There are several recommended motor oils with ZDDP additives that car lovers should look out for.
Amsoil's 10W-40 blend of high zinc and phosphorus levels is a highly recommended motor oil to maximize flat tappet and camshaft life in high performance vehicles, according to Rancho Power. They are specially formulated for use in late-model cars and hot rods that need that extra care and protection. According to Rancho Power, Amsoil's oil is also great for newly designed diesel engines because of its ability to handle the stresses associated with high soot and acid generation.
Precision Engine Tech contributor Mike Mavrigian recommends several high performance motor oils for use in flat tappet engines, such as Castrol Syntec 20W-50. Introduced in 2009, this motor oil is purposely made with increased zinc levels that reduce wear and tear. Mavrigian provides only one caveat for this oil; he feels it is fine for day-to-day use, but since it is a synthetic oil, should not be used to break in a new engine. Mavrigian states that synthetic oils are not recommended for breaking in the ring seatings and lifter rotation of a flat tappet engine.
Mavrigian also points out Brad Penn racing oils as an ideal motor oil for flat tappet engines. These racing oils, made by American Refining Group, are purported to never have a reduced zinc level, which falls in line with the desired ZDDP levels flat tappet engine owners need. According to Mavrigian, Penn Grade 1 is a motor oil that American Refining Group developed specifically as a break-in oil for flat tappet engines. Mavrigian states that this oil is used to ensure proper piston ring seating during break-in. According to Brad Penn Racing, Penn Grade 1 is known as "the green oil" because of its signature green color.
