ZDDP stands for Zinc Dialkyldithiophosphate — it's an anti-wear additive in engine oil that is critical for protecting flat tappet camshafts and lifters. If your engine has a flat tappet camshaft, choosing the wrong oil can destroy the cam within minutes of first start-up.
WHY ZDDP MATTERS: Flat tappet lifters slide directly against the cam lobe with significant contact pressure. ZDDP creates a sacrificial protective layer on these metal surfaces, preventing the cam lobe and lifter from direct metal-to-metal contact during high-pressure sliding.
Roller camshaft lifters use a rolling wheel on the cam lobe — much less sliding friction — so they don't require high ZDDP levels.
THE MODERN OIL PROBLEM: Starting in the 1990s and accelerating through the 2000s, the American Petroleum Institute (API) progressively reduced the allowable ZDDP levels in engine oils. The reason: high levels of zinc and phosphorus can poison catalytic converters over time.
Modern API SN and SP rated oils typically contain 800 ppm or less of zinc — below what flat tappet camshafts require for adequate protection.
WHAT YOUR ENGINE NEEDS: If your engine has a flat tappet camshaft — this includes most engines built before the mid-1980s, plus many remanufactured rebuilds — use an oil with at least 1,200 ppm zinc.
Options include: • Classic/muscle car specific oils labeled for flat tappet engines (e.g., Valvoline VR1, Brad Penn, Joe Gibbs Driven) • Racing oils that have not reduced ZDDP levels • Adding a ZDDP supplement to conventional oil
ALSO CRITICAL DURING BREAK-IN: ZDDP is especially important during cam break-in. See article SR-04707 for the full flat tappet break-in procedure. Our pre-installation checklist specifies the correct oil type for your engine.
Questions? Call 1-844-XPARTS-1 or email support@expediaparts.com.