I totally rip'd this off from another forum... but i figured more information is probably better... so here it is... delete it if you dont want it here.
This guy wrote to Royal Purple regarding exactly this topic.
Here is their reply posted only 2 weeks ago.
Good Morning Mr. Guignard,
What you have read and/or heard about the zinc and phosphorus (ZDDP, the industry standard anti-wear additive) content of motor oils is not completely accurate. The API SM/ILSAC GF-4 motor oil ratings that became effective in ~2004 required a reduction in the maximum allowable amount of phosphorus in an engine oil. This is a de facto restriction on ZDDP anti-wear additive. There is no elimination of this additive, but a reduction of 20% – 35% in 0W-20, 0W-30, 5W-20, 5W-30, and 10W-30 multi-viscosity motor oils. This restriction was introduced under the premise that phosphorus content in motor oil directly affected the useful life of catalytic converters, and OEM’s are now required to warranty their vehicle’s emission system separately from the power train. Since great majority of automobiles produced in the past decade are equipped with roller cam followers (tappets), the OEM’s were not that concerned with flat tappet wear. API SM/ILSAC GF-4 oils are marginal for stock flat tappet cams, at best. If an engine uses a ‘larger’, more aggressive flat tappet camshaft and stiffer valve springs, premature cam and lifter wear is likely.
We at Royal Purple have chosen to hold most of our API rated oils back to API SL/ILSAC GF-3 precisely because of the potential for increased engine wear. Furthermore, in a properly functioning engine, oil consumption is minimal and highly unlikely to prematurely degrade the catalytic converter. For stock build valve trains in the Jeep 4-cylinder and I-6 engines, our 10W-30 (API SL) would work very well. If the camshaft and lifters have been replaced with a more aggressive profile and stiffer valve springs, our 10W-40 would be an outstanding choice (more robust formulation with higher ZDDP content).
One thing to note, though, is that the biggest advantage of using Royal Purple oils is our Synerlec additive. Synerlec creates a high lubricant film strength and thickness, regardless of viscosity. This further reduces the chances of metal-to-metal contact in the engine (reducing wear), increases piston ring seal (more efficient operation), and greatly reduces friction (lowering operating temperatures). All of this contributes to a more allow your engine to run cooler and more efficiently, with less wear, and increases the life of your engine. Another benefit is the increased resistance to oxidation, thereby increasing the life of the oil, and therefore allowing longer oil change intervals.
- Royal Purple SAE 10W-30 (part #01130, quart bottle)
- Royal Purple SAE 10W-40 (part #01140, quart bottle)
Thank you for inquiring about Royal Purple. If you have any further questions, please let us know.
Best Regards,
Christopher Barker
Tech Services
Royal Purple, Inc.
1 Royal Purple Ln.
Porter, TX 77365