Sponsored Links (Register now to hide all advertisements)
The ZDDP was not completely removed. It was just reduced. The higher performance engines of the late 50s through the early 70s needed 1200 PPM of ZDDP for better longevity of flat tappet valve train components. The first reduction brought the levels down to 1000 PPM and further reductions reduced it to 800 PPM so it's still in there but at a reduced amount.