A lot of guys, me included, are switching our older gasoline engine cars to CI-4 oils because the new SH oil has a less robust additive package, especially the ZDDP anti-wear additive than prior spec spark ignition oil, SL being the immediate predessor.

New engines don't need as much ZDDP because most have "roller everything". The reason for ZDDP reduction is because the phosphorous-based combustion by products of ZDDP are believed to contribute to catalyst degradation, however, if your car has relatively low oil consumption, it will probably not be an issue, and if you keep it "forever" it's cheaper to replace the catalyst than rebuild the engine.

If you look at a typical bottle of CI-4 oil you will probably find SL, too, but not SH because the SH spec limits phosphorous content (ZDDP) to lower levels than required to meet current HD diesel engine wear test requirements.

Duke