The difference between premix and OMP is the two stroke oil you would use in premix. The OMP is using motor oil with all the disadvantages it has when it gets into the combustion chamber. Also, you can not use synsetic oil in the engine when using the OMP.
There is a lot more info available in rotary engine related discussions on the internet.
fwiw.
Richard.
From: "Mark McClure mark.mcclure.m3@gmail.com" <flyrotary@lancaironline.net>
To: "Rotary motors in aircraft" <flyrotary@lancaironline.net>
Sent: Sunday, February 26, 2023 8:01:41 AM
Subject: [FlyRotary] Premix vs OMP
I now have 2 engine cores. One is set up for premix and one is set up for OMP. (I of course just purchased a set of SS braided OMP lines before acquiring this 2nd engine)
My search of the listserv (2006-2010 results) shows that overall premix yields a better distribution (at least for the RX-7 engines with 2 OMP lines).
Is the general consensus still that premix is a better distribution? Still recommending .7oz to 1 US Gal?
Thanks,
Mark