only race type oils have high zinc levels [but they are not street legal]because zinc some how destroys the longevity of catalytic converters, so hence to be compliant with au rules zinc levels are lowered.Not good news for flat tappet motors
I even emailed Nulon about their race oils and zinc , they gave me a round about answer 2 weeks later that said yes zinc is lower now[but did not tell me their content] and check with the engine builder and parts supplier to see if their race 15/50 would be suitable for my pre 80 model chev.I thought they might have said something along the lines of yes zinc is low but instead we have?
Amsoil for me