ZDDP isn't being phased out. Actually, the phosphorus is the component of ZDDP that provides the anti-wear capability of an engine oil and phosphorus is what has been reduced to a maximum of 800 ppm in the latest
API Starburst OIls (see
ILSAC GF-4).
Everyone seems to be focusing on ZDDP content as if it is the only criteria of a good engine oil. While the anti-wear capability of an oil is important, the ability to fight sludge and other deposits is also important. Having very high amounts of ZDDP are only really important to flat tappet engines with aggressive aftermarket valve trains but excessive amounts can lead to camshaft spalling and engine deposits.
Esso's Flat Tappet Engine Wear Bulletin suggests that 300-500 ppm of phosphorus is sufficient to protect flat tappet engines. Rather than using Starburst oils in older engines, I think we should be using Heavy Duty Engine Oils (HDEOs) instead. The
Corvair Flat Tappet Engine Oil Article recommends that a CI-4/SL rated HDEO has sufficient ZDDP to protect any flat tappet valve train. It explains that a good CI-4 HDEO has 1000-1200 ppm of phosphorus. Even for the latest CJ-4 engine oil, the maximum limit is for phosphorus is 1200 ppm.
Rather than looking for the Zinc of Phosphorus contents of engine oils, you should be looking for the API certification. Any oil that has met the PERFORMANCE requirements of a CI-4/SL or CJ-4/SM oil should easily be able to protect the older flat tappet gasoline engines. There is no need to use a 40-weight oil (10W-40, 15W-40, etc) in an good-running engine that originally called for a 30-weight oil (30, 10W-30, etc). If you want to stick with a dino-oil,
Shell Rotella T 10W-30 (CI-4/SL) and
Brad Penn HDEO 10W-30 (CJ-4/SM) are readily available. Synthetic 30-weight HDEOs are available too but are available as 0W-30 and 5W-30 because they flow so well in cold temperatures by their nature.
Engine Oil Article