Which oil do you use

[Paul Workman]

Interesting stuff.

As I read the article, I get the "drift" it is fundamentally applicable to pushrod applications (i.e., references to spring tension and lift heights, etc). What I read does not directly addressed is the pressures on cam and lifter contact surfaces as a function of inertia, i.e., speed of rotation.

My point is, whereas the issues with spring tension and valve lift are directly applicable to metal to metal pressure between friction surfaces, the rate or speed of lifting the valve creates considerable forces required to overcome the inertia dynamic. And, it is that dynamic in conjunction with static force that sets the stage for oil performance.

Although the article touches on the fact that ZDDP of API 'SN' is around 800 (I've seen reference to 700 ppm ZDDP for API SN) in order to meet EPA requirements pertaining to catalytic converter life, it doesn't mention that at the same time roller tappets became the norm (primarily in pushrod applications where those necessarily enormous spring tensions and lifts are encountered).

When considering the combination of static and dynamic forces, there's a big difference between 7000+ rpm and 5500 rpm*. So, omitting or failing to acknowledge the differences in RPM and the affect on the dynamic forces speed introduces, I believe there is significant risk the article could leave the impression that oil requirements for relatively low rpm pushrod applications are also directly applicable to higher rpm DOHC applications...but are they????

*The increase of force to accelerate a mass increases at the square of the rate of change.

And, what IS "Mobil-1" anyway? 10W-30 in 1990 isn't the same formulation as it is today. ZDDP is considerably less now than when our beloved motors were designed and built. It may interest some to know that there are perhaps over 50 different oil compilations, all wearing the "Mobil-1" moniker.

There IS a Mobil-1 that has the ZDDP levels recommended by Lotus in 1990, but you won't likely see it on your speedy-mart shelves! I suppose (rather) the safer recommendation would be to grab the HIGH MILEAGE (e.g., 15W-50) stuff instead of the common "SN" 10W-30 with its ZDDP of 700-800 ppm. (However, you "cats" might not like it, which is important if you live where emissions standards are strict.)

Decisions, decisions.... And so it goes.