API-SM rating means your oil has 30% to 40% less anti-wear chemistry compared to earlier ratings. For modern automobiles, you cannot just add a Zinc additive because it may harm the catalytic converter. It is not necessarily the Zinc that is damaging to the catalytic converter.
It is actually the Phosphorus that has to accompany the Zinc to make it work properly as an anti-wear agent. The Phosphorus is the heat seeking agent that over time can react with the precious metals (Platinum, Palladium and Rhodium) within the catalytic converter and damage it to the point of improper operation. Current automobiles need a Catalytic Converter Safe additive that will, most importantly, increase wear-protection without harming emission equipment that is very costly to replace. SR-1 Oil Treatment not only increases wear-protection but, will also increase fuel mileage with additional proprietary friction fighting components.
Features & Benefits
Use ZEP if you don't have catalytic converters