When you click on links to various merchants on this site and make a purchase, this can result in this site earning a commission. Affiliate programs and affiliations include, but are not limited to, the eBay Partner Network.
I have a simple question that may require complex answers!
So i was sitting at home pondering about making my new 13b reliable, thinking wether i should do an OMP delete and have to premix 24/7 or keep burning oil from my oil pan getting that nice carbon buildup (also since i didnt even delete my egr yet and my stock twins are going out...)
Thats when i thought, isn't there another solution to this seemingly everlasting dilemma?
An idea popped into my head about keeping the factory OMP installed but instead of injecting that oil that may or may not be synthetic, it would feed of a simple set of lines that would run to a seperate resevoir that inject low amounts of pure roatry premix directly onto those apex seals.
Seemingly this is something that hasnt been done before, hence me asking if this is even possible,
I mean it should be better since the premix would be much purer/thicker since it isnt really 100% mixed with the fuel at time of injection.
It could technically also be better to the carbon deposite since premix is meant to be burned, especially if you use non-Synthetic premix.
but then again i could be doing more harm than good to the longevity of the engine?
Would this be as easy as hooking the resevoir up or would one have to get an entire retune, and mess with the entire OMP system to decrease/increase the amount injected?
I doubt anyone has experience with this but this could potentially be semi groundbreaking for the future of rotaries, or i could just be yapping. XD
Yep, something we've been doing here in the states for many many years. I'm not sure why, but the Aussies have always seemed to scoff at the idea. Hence why it may seem like this is a new idea. Add in an ECU with the ability to control the omp, and you have the perfect solution for virtually any driving condition and/or apex seal choice.
I've been doing this for years now, since around 2005 on my S5T2 FC, and more recently on my FD. Using the Rotary Aviation / Sohn adapter on both, and a separate pre-mix lube tank plumbed to it. Absolutely love it, as I never have to mess with adding pre-mix to the gas, just need to top off my OMP tank (easy & clean). I typically top off the OMP tank at every fill-up, but I don't need to - tanks are large enough to let me cover roughly 400+ mile trips before I HAVE to top them off.
^That's cool, didn't know anyone else besides RA made a version of the Sohn adapter. FWIW, the actual RA Sohn "electronic MOP adapter" that they market for the S5 FCs & FDs will not fit a turbo S5 FC without having to modify the OEM turbo's oil drain plumbing. Same is *probably* true for the FD version - at least it was with my single turbo FD, I had to re-route my oil drain slightly. Not sure how it fits with OEM twins. Basically adding the RA adapter displaces the stock MOP about 1/2 inch outward from the engine, so it will interfere with anything else that's occupying that space.
^^On my S1 RX8, the Sohn adapter displaced it about 3/4-1". No interference on the 8 but it does make the OMP lines touch some hard metal engine parts vs the non-displaced routing so a potential failure point to watch for. I should go back and try to pad that section to decrease the risk of line failure... someday...
I have a simple question that may require complex answers!
Cleanly packaging an appropriate size reservoir with the stock twins always seemed like it would be a bit of a hurdle. And you better not let it leak or otherwise run dry. Fitting the adapter with the engine in the car wouldn’t be that fun either. And I bet you’ll still be dealing with some carbon, even with the expensive designer “rotary” premix oils. The Sohn adapter was a clever option, but there are others these days. IMO there is no perfect answer or an absolute right choice. Everything comes with advantages and baggage. The “complex answer” is deciding what will work for your car, its use, its state of modification, your wrenching abilities, and your budget. You owe yourself a little research here on the form before making a choice…
*Functioning OMP
*OMP delete and premix
*Sohn adapter and reservoir
*Functioning OMP with WI
*Functioning OMP and reduced premix with WI
^^On my S1 RX8, the Sohn adapter displaced it about 3/4-1". No interference on the 8 but it does make the OMP lines touch some hard metal engine parts vs the non-displaced routing so a potential failure point to watch for. I should go back and try to pad that section to decrease the risk of line failure... someday...
Now that I'm looking at mine again, you're right - the displacement is more than 1/2 inch, that thing is closer to 1" thick. Never had problems plumbing the RA adapter with the stock OMP lines lines on my FC or FD though, there was enough slack in the lines where I was able to route them without any interference/rubbing issues. I purchased new OEM lines when I did my installs, so the new lines were probably a lot more pliable than an old set of lines with lots of miles on them.
unfortunately the oil injector placement in the engine still doesn't lubricate the seals all the way across during engine operation, premixing is still the most reliable method of lubricating your side and apex seals.
this is a better alternative to crankcase oil though.
Don't forget when you a deaccelerating, you are no longer utilizing the fuel injector or spraying premix the whole time you are off the throttle; neither is perfect.
Don't forget when you a deaccelerating, you are no longer utilizing the fuel injector or spraying premix the whole time you are off the throttle; neither is perfect.
i've heard this brought up many times, you gotta keep in mind that premix doesn't burn off readily and should still lubricate for a period of deceleration. i've had apart many premixed engines that had minor wear after many many miles.
I've heard people claim that the deceleration after a dyno pull might be a long enough time that apex seals can get damaged if there is no premix injected because of decel fuel cutoff. If that's accurate, then coasting down a mountain might be long enough time to do damage. I think I've seen some tuners or builders recommend to disable decel cut on cars that have the OMP disabled and rely on premix.
if someone is claiming an engine was damaged on the dyno due to the fuel cut and premix, they're blaming their own tuning inabilities on anything they can grasp at.
if a person is really that worried, do both, premix and run the OMP. can't go wrong that way. i however would follow this thread and use an external 2 stroke oil injection through the OMP rather than the crankcase oil which actually wears the seals rather than save them, you can see this on 100K+ mile rotor housings by following the wear groove from the oil injection port.
as an aside, at about 75k miles when i was getting ready to do an engine rebuild i ran the car with no premix at all for 2 full tanks of fuel. the engine ran fine with zero apex seal lubrication at all and still made it to 90k miles before eventually losing enough compression to warrant the rebuild. it was already getting rather low at 75k even before i put it through that. doesn't sound like a lot but it's a fair amount on a modded rotary. the rotor housings were still usable with minor reconditioning work, it's not a promotion to do such a thing but i like to experiment.
Last edited by notanymore; Aug 7, 2025 at 09:34 AM.
I use an earlier version of https://www.rotaryaviation.com/store..._Adapters.html which uses a large O ring for sealing.
It gets it Idemitsu Premix Oil from a pint container near where the fan relays were located.
Then I also mix 1/2 oz of it with every gallon of gas in the tank.
Feeding Premix INTO the OMP!
