It’s All About the Zinc – High Stress Wear Resistance with Penrite Oil!


It's All About the Zinc – High Stress Wear Resistance with Penrite Oil!

by Mike Kojima

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.


Production based race engines are particularly hard on their oil.  Project G20 is a prime example, stock oil pump, turbo engine with an oiling system not originally designed for a turbo.  Driven on a road course in wheel to wheel racing means the car sees a lot of wide open throttle for extended times under gruelling conditions.

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.


Turbo engines like the one in our LSR S13 are particularly hard on oil.  Turbos depend on the oil for cooling and lubrication.  Sometimes spinning to over 100,000 rpm in the proximity of 1400 degree heat, a turbo really puts the hurt on oil through aeration and heat related break down. If there is a Motorsports venue harder on oil than Land Speed Racing, we don't know of it.  The engine is at full throttle at maximum rpm and boost for several minutes at a time.  Our LSR car does not have a dry sump and will be pushing the oiling system right to the edge.  We have had bearing issues in the car before. High viscosity synthetic racing oils with a full zinc additive package like Penrite can really save the day here and you can bet that we will be running it.

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.


High ZDTP synthetics like Penite are particularly useful for improving engine life in racing engines with a small sump capacity like the Nissan SR20.  Anti wear additives help eliminate the chance of metal to metal wear when the oil is hot and aerated which happens quickly in small sumps. 

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. 

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