OVERKILL
$100 Site Donor 2021
Yes, that's correct. The engine is developed and then testing is undertaken to confirm that the oil that may have been assumed to be appropriate, is. Sometimes this can change in service if the oil is deemed inadequate or the OEM, working with the oil company, decides that something is better. This was kind of along the lines of what happened with GM and M1 5w-30, which they spec'd forever, and then their transition to M1 ESP 0w-40.Someone please explain this to me... I always thought the oil is specified to the engine's design, engineering and application, not the other way around.
Sometimes it goes the other way though too. M1 0w-40 (a full-SAPS euro oil) was the original oil spec'd for SRT engines. When SOPUS took over, an SRT-specific 0w-40 was developed, which has no Euro approvals and a pretty vanilla SN/GF-5 additive package; it basically looks like somebody turned your basic EC 5w-30 into a 0w-40. Yet, FCA determined that this was more than sufficient for these engines, none of which have turbos to share the engine oil with.
Ford transitioned a huge list of engines that spec'd 5w-30 to 5w-20 after internal testing confirmed that it was safe to do so. BMW switched between 10w-60 and LL-01 oils for at least one M-car engine (S62). Ford also spec'd 5w-20 and 5w-50 simultaneously for the same engine depending on how the car was configured.
Going back to its most elementary, in the cradle of SBC hotrodding, the "10psi per 1,000RPM" rule came about as the result of engines being built loose for more power and trying to determine what viscosity should be run in them. This was what ended up being sufficient per "back of the napkin", so if you had really opened things up but 20w-50 got you there, well, you were OK.