How the evolution of valvetrains redefined the limits of engine performance
From the simplicity of the flathead to the precision of overhead cams, the way an engine breathes has changed everything. But the real story lies in the microscopic battle between metal and oil, where a single missing film of lubricant can lead to catastrophic engine failure.
The history of the internal combustion engine is a progression of valvetrain architectures: the flathead, the overhead valve (OHV), and the overhead cam (OHC). While older vehicles frequently rely on flathead or OHV designs, the modern automotive landscape is dominated by OHC configurations. A defining characteristic of these older engine generations is the use of flat tappets to actuate the valves, a mechanism that creates an incredibly demanding environment for engine lubricants.
The primary challenge in a flat tappet system is the intense physical stress placed on the interface between components. This specific area of the engine experiences high heat, high pressure, and high shear stress. Because the camshaft moves rapidly against a relatively stationary tappet, the lack of a continuous oil film would result in metal-on-metal contact, causing rapid and severe wear. To mitigate this risk, engineers and enthusiasts have historically relied on specialized oil additives.
One such additive is ZDDP, which functions by creating a sacrificial layer that wears away instead of the camshaft or tappet. This necessity is why certain oils, such as Mobil 1 Classic—specifically formulated for vehicles produced between 1951 and 1996—contain higher concentrations of ZDDP than contemporary engine oils. In contrast, modern engines have transitioned toward roller tappets. These rollers significantly reduce friction, allowing for more aggressive cam profiles and reducing the engine's dependency on high levels of ZDDP to prevent wear.
Source: This Tiny Engine Part Changed Everything - Flathead vs OHV vs OHC!
