Shell.ca was very open and forthcoming.
SHELL REPLY:
As I explained to you over the phone Phosphorus and Zinc content is not a criteria to be used in selecting the right oil for an engine. Rotella T 15W-40 meets API CJ-4, and supersedes CI-4 and previous specs. Maximum allowable Phosphorus content for API CJ-4 specified oils is 1200ppm. Phosphorus (S) and Zinc (Zn) comes from ZDDP additives used in the oil.
Although, S and Zn content of Rotella T 15W-40 was slightly lowered to meet CJ-4 specification, the performance of the oil has not been compromised compared to previous Rotella T with CI-4 spec. In fact, new Rotella T 15W-40 shows better wear resistance, deposit control and reduced emissions. This was achieved by the improvements in additive technologies and Shell's advanced oil formulation techniques.
However, if a customer is still insisting on a product with CI-4 spec then our Rimula Premium 15W-40 can be offered.
Technical Representative Lubes & Fuels
Shell Canada Products
CASTROL REPLY:
Unfortunately Castrol's oils formulations are proprietary information and are not released to the general public.
However, we can tell you that the ZDDP levels have been reduced.
We DO NOT recommend any of our GTX Dino oils for flat-tappet engines; we recommend Syntec for older cars.
Castrol Consumer Relations.
I called Castrol to confirm this.
They do not recommend any of their Dino oils (Including 20W50 and 15W40 Diesel) for our air-cooled engines (Or any engine with flat tappets)
So, forget about 20W50 GTX for track days.
For me, Castrol is out; Shell is in.
I like Diesel oil and plan to use either Rotella-T 15W40 with GM-EOS or Rimula 15W40 for the 911.
(The reason why I like Diesel oil is experience: Numerous high-mileage vehicles like my present old Volvo 240 with 300.000 km, original engine on 15W40 Diesel oil without EOS)
Any thoughts?
