STP & Dilution Math
To address the issues raised to date:
Crane Cams lube:
From the looks of both the document title and the format of the page, it looks like the analysis that you linked to was performed at Blackstone. For testing oils with elemental concentrations in the range of normal oils, Blackstone is a reliable and inexpensive lab to use. We use them often for this reason, however like all other "consumer" oil analysis laboratories, their procedures are designed for oils whose elemental makeup is in the normal range for oils.
A giveaway that the test may be in error is the fact that the phosphorus reading is higher than the zinc, with the P to Zn ratio of 1.03:1. In most ZDDP molecules, the ratio of P to Zn is around 0.9:1. Some ZDDPs are processed with an excess of zinc compounds, which makes the ratio even lower, with most commercial preparations in the 0.7:1 to 0.8:1 range, as are both GM EOS and ZDDPlus.
Our tests of the Crane product at SRI (Soutwest Research Institute) showed numbers considerably lower than those given by your link to the Bob the Oil Guy website.
When testing concentrates, special dilutions must be done before testing to bring these elemental concentrations down into the range of the equipment. We have worked closely with Blackstone in the last few months to perfect a procedure specifically for ZDDPlus and other concentrates after initially getting erroneous reports from them. We knew the initial reports were in were in error, because when we first qualify a lab, we send samples both to the prospective lab and to a well-established petrochemical industrial lab such as SRI, which gave us a different analysis.
Unfortunately ASTM analyses such as those done at SRI are costly, and can be hundreds of dollars per test for a single element.
After working with Ryan at Blackstone on this issue for a few months, we now feel that if someone sends a concentrate sample and specifically tells them that it needs to have an up-front 40:1 dilution using white oil before testing, they should be able to get reliable results.
BTW, this subject is covered in greater detail in our ZPlus Tech Brief #7, available at
ZDDPlus™ - ZDDP Additive for Classic Cars - Agricultural Equipment & More
STP Dosing:
OK, since you obviously have a handle on the math, I would say then the issue here is one of what is considered a significant change. We would consider that spending the money for a bottle of STP and diluting over 8% of your oil with an unknown gooey oil to merely get an 8.2% increase in P or Zn level not the choice that an engineer would make. Since most SM oils average around 600 ppm of P and 800 ppm of Zn, a single bottle of STP does little to address the issue. It was this exact situation that led us to make ZDDPlus.
Research clearly indicates that adequate protection for solid lifter cams in high-performance engines requires ZDDP resulting in a phosphorus level well in excess of 1000 ppm. Since you are good with math, you should be able to see that a bottle of STP does little when added to 5 quarts of API SM oil. If you factor in depletion of ZDDP over the life of the oil change, it is wise to start with a level considerably higher than 1000 ppm.
For more information on depletion, see ZDDPlus Tech Brief #8, available at
ZDDPlus™ - ZDDP Additive for Classic Cars - Agricultural Equipment & More
One bottle of ZDDPlus will increase the Zn and P levels ten times that of the bottle of STP, making it a better buy on an ounce for ounce basis, and you do not end up diluting your oil with an unknown oil.
