It's All About the Zinc – High Stress Wear Resistance with Penrite Oil!
We get a lot of oils and lubricants to evaluate at the MotoIQ office and for the most part we have had good results with the latest high quality synthetic motorsports oils that come across our desks and into the crankcases of our various race and project cars. When it comes to quality oils we get pretty uniform results, clean burning, low deposits and good wear of the engine's internal components.
However, when the wick is turned up, not all oils perform alike, especially today. Today we are seeing more lubrication related failure of valvetrain components and bearings than in the past. Some of it is because technology learned over the past few years has allowed us to make more power than ever before. The perfect example of this is when we are pushing the limits of the stock factory wet sump system when racing, as an example, a powerful forced induction engine or a high RPM naturally aspirated engine spinning at much higher revs than stock on a road course.
Under these conditions, even with coolers, good windage trays, crank scrapers and bigger sump oil pans, there is quite a bit of aeration of the oil and localized heating. It is common for the oil to contain over 40% entrapped air by volume. When this frothy and hot oil gets sucked up by the oil pump, this much compromised for lubrication oil, is getting circulated right back into the engine.
Even if you are getting decent oil pressure, with whipped oil, your engine's bearings and valvetrain will be fighting for survival. What we are saying is that race engines really need the cool, constant pressure and de aerated oil supply that dry sump systems provide but dry sumps are beyond the budgets of most of us.
Another thing that has happened lately is that engine oils, even well known “good” brands of synthetic aren't what they used to be. This is largely because the amount of zinc-di-thiophosphate or ZDTP for short has been declining in modern oils. ZDTP is one of the best anti wear additives available for an oild package, being highly effective in reducing metal to metal contact inside an engine. It is also highly soluble in oil.
The reason why the ZDTP content has been slowly reduced from engine oil is that the phosphorus in it is a powerful poison to catalytic converters and oxygen sensors. It literally gives the catalytic matrix a phosphate coating over time blocking it from working. As emission laws have gotten tighter the amounts of ZDTP ?allowed in oil have also been reduced, beginning in 1994.
When the API SH oil rating was introduced in 1994, a limit of 1200 ppm for ZDTP was set. Now to meet the current API SN rating, many manufacturers have lowered their ZDTP limit to 800 ppm. So in many ways the oils you were running a few short years ago have more protection than what you have now.
The area of the engine where the effect of lower ZDTP will first be noticed, particularly on a street car, is going to be the valvetrain. A car's valvetrain is the part of the engine that has the highest contact stress and unlike the other parts of the engine, the contact stress is actually worse at low rpm!
Most modern engines have roller cam followers in order to reduce friction. Roller cams don't need as much anti wear additive to survive. Many high performance engines still have sliding finger followers, flat tappet lifters or shim and bucket direct acting valvetrains that depend on a high strength film of lubrication to survive. When stock, these engines may still be adequately lubricated with current API spec oil but when modified with higher spring pressures and more aggressive cam ramps, lubrication can be pushed beyond the oil's limits.
Many engine builders, ourselves included, have started to notice accelerated valvetrain wear since the introduction of SM and tighter standards. There is a direct correlation between an increase in valvetrain wear related failure and the amount of ZDTP in oil going down below 1200 ppm. This has been particularly disastrous for push rod V8 engines with radical cams, high valve spring tension and flat tappet lifters. We have also noticed more wear in finger follower valvetrain engines like the Nissan SR20DE in racing use particularly on the nose of the cams.