Idemitsu Rotary Engine Oil
 

As always, I check the forum for older threads that cover the topic of engine oil, since it is a common subject. This time, I could not find anything on Idemitsu Racing Rotary Engine Oil. I am curious about this product because it is a full synthetic oil, I have been using it in my 1990 RX-7 since purchasing it in 2016, and it has come to my attention that Mazda does not recommend using it. I need to know the truth about running this oil in my stock engine with the factory OMP. Will this oil cause problems with carbon deposit buildup? Since it is intended for racing, is this oil meant to be used in the oil pan only, and the fuel pre-mixed with the proper lubricant? I bought the car with something like 128,350 miles in 2016, and it now has 133,560 miles on it. As soon as I acquired it, I ran two cans of "Sea Foam" through the engine to remove as much carbon as possible. After 5200 miles, I can't imagine much buildup of carbon from using Idemitsu if it indeed does not burn cleanly and should not be used with the factory OMP.

While you may not find much about Idemitsu. Do a search about synthetic oil in rotary engines, you will find all the information that you will need. As a general rule of thumb, synthetic oil is not recommended for rotary engines with and OMP that uses engine oil.

It's weird they don't specifically say it's applicable to OMP equipped engines like Royal Purple does.
Closest they come to saying it from the product page:
Their flyer says the oil formula is based on what was used in the 787B which used an OMP.
I still wouldn't be sure unless they explicitly say so.

Update on Idemitsu Rotary Engine Oil
 

As advised, I spent some time doing research regarding the performance of Idemitsu Rotary Engine Oil. Mazdatrix has an article reviewing and offering their opinion on this product. According to Mazdatrix, Idemitsu is the only synthetic oil that they would recommend for use in any rotary engine utilizing a functioning OMP. This oil is designed to burn cleanly without leaving carbon deposits behind, unlike other synthetics. Now this matches the claim from Idemitsu that their rotary engine oil "able to minimize deposits on your apex seals". This can infer that the claim is valid with use of the factory OMP. Otherwise, I don't know and don't think that engine oil from the sump can or could make it's way to the apex seals without an OMP.

Other research that I conducted found that the OMP system of FC S5's injects about 25% of the oil an OMP from the S4's as a result of Mazda's struggle to control emissions. With this in mind, not only am I glad to be using Idemitsu in my current engine, but am thinking and planning of using some Idemitsu pre-mix in the future once I go to the Racing Beat header and presilencer combo. This is assuming that even Idemitsu synthetic pre-mix will clog up my catalytic converters in the current factory exhaust setup. I certainly want to use both this particular engine oil,(10W-30), and the premix with the new engine I am building given how miserly the factory OMP is. Of course, I will use a quality conventional mineral-based oil along with pre-mix during the break-in period.

I must have tore down at least 10 rotary engines in wrecking yards since 2010, and in every case, I find deep, long gouges in the chrome wear surface of the rotor housings of these engines. I can't help but think that this kind of drastic wear is attributable to the lack of adequate lubrication of the apex seals from the factory OMP. Considering the exorbitant cost of rotor housings these days, it pays to make sure that there is more than enough lubrication to obtain the maximum amount of life and performance from them.