Automobile manufactures have lobbied (and governments have mandated) to reduce the levels of zinc dithiophosphate and phosphorus in motor oils to increase the service life of catalytic converters.

They are highly effective as an extreme pressure anti-wear additive. However, it's probably not overly critical on our SOHC motors as they are equipped with roller-tipped rocker arms, where most wear from the lower ZDDP concentrations manifests itself.

Current Mobil 1 specifications and approvals:
http://www.mobiloil.com/USA-English/...duct_Guide.pdf