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Following on from some on-line chatter regarding which oil viscosity best suited a particular engine in relation to power, we were curious too so decided to undertake some testing in order to have certainty on this matter.

The test results certainly surprised us and dispelled some myths and assumptions.

The test method used our Rototest chassis dyno which is accurate to <1%, measurement repeatability to <0.05%, zero tyre/grip/camber/toe interference, correcting to DIN 70 020 making the data sets entirely representative.

We wanted to ensure testing parity between the oils so endeavored to equalise the oil temperature to an operating window of 75-76 degrees, engine coolant temperature window of 90-95 degrees, taking 6 test runs then taking the average power (not peak power) of the runs in order to gather accurate and representative data.

Note that we were exclusively looking for the impact on engine output, not engine life/wear or temperatures etc, and that the testing is confined to HKS, Millers, Joe Gibbs and a cheap “off the shelf” Carlube oils. There are many other brands of oils that may perform better, worse or similarly.

Out of interest we also tested ZX1 oil additive which claims to be the ultimate friction eliminator, to assess it’s impact on performance.

The methods and results are shown on the linked attachment. Oil Testing – Analysis


  1. Whilst it may seem intuitive to assume that higher viscosity oils will reduce engine output due to higher parasitic losses, that actually isn’t the case among the oils tested.
  2. Price isn’t always the determinant of performance among the oils tested, although it may have other beneficial attributes.
  3. There is a significant variation on cooling effectiveness between the oils.
  4. ZX1 is effective by yielding approximately 2% more power.