This is the answer I got from Shell, when I asked about the new formulation. I use it in my older muscle car engines, and recommend it to my customers engines.

Hi Jim,

Our CK-4 formulation still has about 1200 ppm of zinc and 1100 ppm of phosphorus, and should still be able to provide adequate protection for flat tappet engines. I’ve attached a brochure that goes over the chemical changes in detail.

I hope this helps.

Best regards,

Aly
Shell Technical Information
1-800-237-8645 (Option 3, 1)

Safety and technical data sheets for active Shell products can be found at www.epc.shell.com.