low speed pre-ignition

I had many cars that backfired when I used some oils. I knew it had to do with something about the oils I kind of knew what it was. My dad was a oil engineer and way back he had a 1982 volkswagen rabbit diesel. He would look for oil that had high levels of Molybdenum. I remember he said something about the Calcium clumping together holding in heat causing a pre-ignition in the cylinder. 

In engines today it is true Molybdenum does help against LSPI. "Molybdenum compounds, for example, not only provide frictional benefits, but also have been shown to decrease LSPI when used at high levels." But Molybdenum also has sulfur in the mix and with a hot engine tends to make sulfuric acid so with that the Calcium is needed to keep it away. Also with the modern engines they have small bearings so because of that there is damage to the bearings at idle if there is a backfire with a 20W oil. The oil does not have enough cushion being the oil is like water at low speeds so if there is a jolt to the bearings with weak oil at low RPM!

So you can see the mess in oils in newer cars but it's being worked on! I am not pushing any brand just pointing to the effort to fix things. VALVOLINE has oil battle ready against LSPI so it's being fixed!
https://www.imoa.info/molybdenum-uses/molybdenum-chemistry-uses/lubricants.php
http://www.pqiamerica.com
https://www.valvoline.com/our-products/motor-oil/modern-engine-full-synthetic-motor-oil

~~~~~low speed pre-ignition shedding light on LSPI
Turbocharged, direct-injected (DI) gasoline engines are rapidly growing in use because their design provides improved fuel efficiency when compared with other gasoline engine designs. In particular, there can be significant efficiency benefits achieved when a smaller, turbocharged DI engine is used to replace a larger, conventional engine of the same power. However, the higher power density of these engines makes them prone to a phenomenon called low speed pre-ignition (LSPI). LSPI is an abnormal combustion event in which the fuel-air mixture ignites before intended, causing excessive pressures inside the engine's cylinders. In mild cases, this can cause engine noise, but when severe enough, LSPI can cause engine damage. There are several factors that contribute to LSPI, of which lubricating oil has been observed to be one.
https://www.oronite.com/about/news/low-speed-pre-ignition.aspx