Thought I'd share an article I ran across in another board. Specfically, on Oil API ratings. Other interesting info inside as well.

API SN. Intended for 2007+ gasoline direct injection cars with ceramic catalytic converters instead of metallic cats. As large amounts of zinc and phosphate (ZDDP) and carbon ash (SAPS) are harmful to the ceramic material, they have been replaced with other additives. More detergents have been added to prevent carbon and sludge build-up (see the section below on Direct Injection engines). This is not bad oil for these engines and if you still have factory cats this is the oil rating you should be using. Bonus points if the bottle carries a Mercedes 229.5 (MB229.5) approval as Mercedes standards are among the highest of OE manufacturers. If you need extra protection for track use or aggressive driving, switch to a thicker viscosity.
API SM. 2005-2010 models but this doesn't really apply to BMW. Use an SN oil for a car that retains all of its factory equipment.
API SL. 2005 or older. Many people consider SL to be the last "good oil" before ZDDP levels were reduced. We recommend an SL oil for pretty much all cars built before the E90 generation: E85, E83, E63, E60, E53, E46, E39, E38, Z3, E36, E34, and E32. It can be used in E30 and older models too but only in thicker viscosity. These cars can use an SN oil but SL is much more appropriate. It can also be used in newer cars (E9X, F3X, etc) that have had cats removed (such as race cars) or street cars converted to metallic cats. The higher ZDDP levels will be advantageous in aggressive driving.
API SJ. 2001 and older. The original formula for cars built in the 1990s or older but you're not likely to find it anymore. See API SL above.

https://www.bimmerworld.com/BMW-Engine-Oil/

 

I'm going to show my ignorance about catalytic converter history here, but I thought early cars used a bed of pellets coated in platinum (and other precious metals), then in the early '80s the technology changed to a ceramic brick or honeycomb coated in the same precious metals. Or in other words, for all years of BMW sited in that article, they would all have a "ceramic" converter (core). I'm not aware of any that use a metal core.

I thought the zinc and other additives destroyed (coated) the precious metals....not that they attacked the ceramic.

Someone with more knowledge please....

 

I don't know. I drive a Firebird. I put oil in the top, it blows out the tail pipes and run out on the ground underneath. I suppose all that would matter if I drove some Cadillac Converta.

 

I don't know a thing about them either, but this website covers a lot of issues

https://www.catalyticconverters.com/construction/

 

There is a lot of debate about ZDDP levels and the effect on engines. It is true that ZDDP levels are lower than years ago, but it isn't gone. The effect of phosphorus in particular degrades the catalyst. The degradation is related to the active material (precious metals) in the catalyst and it's effectiveness. It doesn't matter what the substrate is--ceramic, metallic, pellet, brick. So, as you burn oil or it leaks past the rings, the additives flow down the pipe and damage the catalyst coating.
Now, lower ZDDP level isn't necessarily a panic level issue. The newer oils have other chemistry to maintain or even improve performance. While some of the test engines have changed over the years (no one builds 1980's flat tappet engines in production any more), you can go look up the API test specifications and current test engines. They still test with flat tappet engines. The newer oil formulations must pass tests with equal or less cam and lifter wear than the old high ZDDP oils. In extreme cases, you can use racing oil, ZDDP additives for initial break in or what ever you like, but don't fear the new oils for most applications.

 

Tell that to all the guys whose flat tappet engines suffered premature cam wipeout, doe to low ZDPP levels.

 

The challenge is understanding how you can know that the problem was caused by reduced ZDDP and not some other fault. Many times the true root cause is unknown, because the evidence is lost when the cam lobe or lifter breaks down. This usually means that the finger is pointed at the first suspect, in this case ZDDP. So, "ZDDP concentration went from 1100 ppm to 800 ppm, that's why my engine failed". It is quite possible that if someone is running a flat tappet cam with 50% higher spring force than stock, it falls in the "extreme" category as I referenced above. Maybe more ZDDP would help, maybe not. There is also a very large effect of the base stock and the rest of the additive package in an oil. It's just not as simple as pointing at a single factor. There are other additives that can be used to improve wear resistance in the oil.
Examples:

• My father-in-law lost a cam in a 1978 305 Chevy at about 30,000 miles using 70's Mobil oil - certainly plenty of ZDDP there. Rumor back in the day was that Chevy had a batch of cams with improper heat treat.
• I just wiped 6 lobes off of a new cam in my 305 on break-in with high ZDDP VR1 oil. Guess what- I found that the engine builder missed a fine crack in the block and it was leaking coolant into the oil.
• On the other hand, I've been running my 428 Cobra Jet Mustang for nearly 40 years on the latest "low ZDDP" oils off the shelf (Valvoline and Mobil 1 10W-30) - the cam is still working fine.

My point is that there are many variables and you need to look at the physics of the application. My preference for a normal street engine is to find a high quality oil that meets the latest specs, API and ISLAC, and not worry about it. If you're pushing the envelope significantly beyond where the original design engineers intended (contact pressure and velocity), then consider additives or special oil. But, be careful--too much ZDDP can be as bad as too little.

 

I've been running Valvoline VR1 Racing Oil 10W30 in my flat tappet 327 with zero cam issues so far. The engine was built in 2011. Was running 20W50 until I found out they also had a thinner 10W30, just no one around here carries it. I order a case online when I need it.

 

I'm not saying all cam failures are ZDPP related. Chevrolet certainly had a lot of improperly hardened cams, in the 70's. But lots of properly built /re-manufactured engines and older engines suddenly switched to low ZDPP oils, suffered traumatic cam failure.

I ensure my older cars have proper ZDPP levels, others can take a chance, if they wish.