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.