A few years ago when I was trying to decide what oil to run in my Vette on the track, I looked into Royal Purple in detail and was really turned off by what I found. Royal Purple did not perform well in the used oil analysis reports I reviewed at the time. Royal Purple's website, http://www.royalpurple.com/
, does not provide a lot of information on their products, nor do they indicate what type of synthetic basestock they use.
What most people don't realize is that "synthetic" as a term has not been defined by the API. There are synthetics, and there are synthetics.
Redline comes right out and says that their oils are ester based synthetics:
The API classifies ester based synthetics as a Group V synthetic.
AMSOIL comes right out and states that they use a PAO based synthetic:
AMSOIL Corporate Homepage
(try typing in PAO in the search box and see how many pages come up)
The API classifies PAO based synthetics as a Group IV synthetic. (Mobil 1 uses a PAO basestock as well)
Royal Purple doesn't say what their basestock is which really turned me off when I was trying to decide what oil to use in my Corvette. Is it a Group III, or highly refined petroleum oil, the lowest performing of the "synthetic" groups (and least costly meaning higher profits for the company), or is it a Group IV or Group V? Why don't they say?
Redline, Mobil 1, AMSOIL all list data on their oils including such key performance ratings such as High Temp High Shear ratings. Royal Purple doesn't share this info.
Even a check of Royal Purple's MSDS shows a hesitancy to share info:
"The precise composition of this oil is proprietary. A more complete disclosure will be provided to a physician or nurse in the event of a medical emergency."
In my opinion, Redline is superior to Royal Purple if for no other reason than it is a known quantity. Royal Purple has a really good rep on the forum, mostly because guys switch to it, find it is better than the stock non-synthetic fluid and report how much better it feels, thus a legend is born. In my opinion, any good synthetic will feel better than the stock fluid.