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OMP mod/improvement Idea

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Old 03-17-17, 04:43 PM
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OMP mod/improvement Idea

Hey, sorry if this has been covered, I searched but obviously there are a ton of OMP threads.

Anyone ever thought of switching to an S4 13B 4-line OMP on an 13B-REW? Or better yet, drilling and tapping the REW OMP for 2 extra lines? (Which it appears it may have been designed for initially? I don't have one in front of me to take apart and confirm, unfortunately).

Now you are probably saying, okay... but what will you do with the extra injectors? Well, a 4-port LIM like the one from Xcessive -- provided you have retained the factory dual fuel rail setup -- leaves you with two empty ports to the primary runners. A little fabrication and these ports could easily accommodate oil injectors. Best of all, on the S4 13B, the 2 additional oil injectors are placed in almost the same place.

Reasonable questions to ask:

-Would the pump be able to supply the extra 2 lines?
Not sure... PFC or other EMS may be needed to have it functioning optimally. (This is assuming the 13b-REW pump could be modified)

-Why were the extra lines removed from the 13B-REW to begin with?
No idea... the Renesis went back to 4 lines but all 4 went to the apex seals, as many of you know.

-Wouldn't one set of side seals/one side of the housing get more lubrication than the other by using only the primaries?
Yes, but would would you rather both sides receive nothing, or one side receive something? Also, this *was* a factory implemented system at one point, so it can't be that bad, right?


The mod would be used in conjunction with a separate 2-stroke oil feed. Not sure if I would premix but a pretty minimal ratio would probably suffice with this setup, which would make the fuel injectors happy.

Disclaimer: I don't actually have an FD lol. I'm just a guy that likes rotaries and loves theorizing with like minded folks. Sorry for wasting your time if y'all have been down this road already.

I'm eager to hear your insights, thanks.

Last edited by Oggy; 03-17-17 at 04:46 PM. Reason: clarity
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Old 03-17-17, 06:11 PM
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The mounting faces of the S4 and FD OMP are totally different. There really is no benefit to all this work when you can just premix. I know that people want to retain OMP in some cases, but I prefer to run synthetic oil in the crankcase. Synthetic oil doesn't burn, so premix it is for me.

Also, the ports on the xcessive unit are similar, they are not the same as an S4 LIM. The OMP openings are tiny and you would probably need to machine or weld up something for the banjo bolts to thread into. Why you would spend all that money on an xcessive just to run OMP is beyond me.
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Old 03-17-17, 07:06 PM
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Not everyone likes premixing, I know I don't. What your saying has been done before. I have a s4 mop to do this in the future when I get off my...Anyhow I'll link the build thread.
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Old 03-17-17, 07:10 PM
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https://www.rx7club.com/build-threads-292/93-vr-bw475-1036950/page7/
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Old 03-17-17, 07:18 PM
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Quote:
Originally Posted by ACR_RX-7 View Post
The mounting faces of the S4 and FD OMP are totally different. There really is no benefit to all this work when you can just premix. I know that people want to retain OMP in some cases, but I prefer to run synthetic oil in the crankcase. Synthetic oil doesn't burn, so premix it is for me.

Also, the ports on the xcessive unit are similar, they are not the same as an S4 LIM. The OMP openings are tiny and you would probably need to machine or weld up something for the banjo bolts to thread into. Why you would spend all that money on an xcessive just to run OMP is beyond me.
Thanks for the reply!

Okay so S4 OMP is out, but the possibility of modify the FD OMP remains. If you look at the image I linked it looks like it may be as simple as drilling and tapping two new holes. (Here is again, and one without the illustration.)

Agreed it's not worth getting the Xcessive just for this mod... absurd actually. So lets just assume you already have one, and choose to retain your separate primary fuel rail. The unused injector ports must be plugged anyway, why not have a machinist turn plugs on a lath that are drilled and tapped for the OMP banjos? Seems like a great way to make use of something that would otherwise be useless, no?

I too would want to run synthetic in the engine so the OMP would be fed from a separate tank of 2 stroke oil. I have my reasons for keeping it... but I understand the OMP vs. premix debate has been beat to death so lets not take this thread there.
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Old 03-17-17, 07:38 PM
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Quote:
Originally Posted by silverTRD View Post
https://www.rx7club.com/build-threads-292/93-vr-bw475-1036950/page7/
Just read through the thread, great link!

Wish the pictures still worked but still a great discussion. Someone in the thread brought up an interesting point about the FD electrical pump allowing for the OMP to be controlled by manifold pressure and RPM instead of throttle position like the S4 mechanical pump. Another reason to modify the FD pump, if it can be done.

However, it seems that most people's reasoning for adapting the S4 pump if for mechanical reliability, not for the additional injectors. Interested to hear some people's thoughts on this.
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Old 03-17-17, 07:46 PM
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Some use the s4 because they don't have inputs on the Ecu for the mop. The mechanical mop solves that problem. If I remember correctly Chris added injectors to the secondaries in the lim.

If if you were to use different lines than OEM couldn't you just put a Y in each line to have 4 injectors for the FD?
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Old 03-17-17, 08:12 PM
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Originally Posted by silverTRD View Post
Some use the s4 because they don't have inputs on the Ecu for the mop. The mechanical mop solves that problem. If I remember correctly Chris added injectors to the secondaries in the lim.

If if you were to use different lines than OEM couldn't you just put a Y in each line to have 4 injectors for the FD?
Did he? I thought he might have but couldn't tell for sure without the photos.

Yes do I suppose you could just add a Y in each line, lol. Probably the simplest solution, and that's usually the best one. That would also let you use the 'better' Mikuni pump as well.

I'm still looking for pictures of the Denso FD OMP disassembled just to see if modification is possible. Just out of curiosity really... the only benefit is it would look super OEM.
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Old 03-17-17, 09:58 PM
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For anyone following, it appears the FD Denso OMP could be modified for additional lines.

I found a photo of the 20b OMP, it appears externally identical to that of the FD. The only difference being that the 20b pump has the additional ports opened up already. I can not know for sure if they are the same on the inside as well, but I think it's plausible.

I guess the only remaining question would be in regards to the potential effectiveness of the two additional injectors in the LIM. Any opinions/insight would be appreciated.
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Old 03-17-17, 10:17 PM
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what makes you think 4 injectors are better than 2? the FD rotor housings generally last the longest of all rotary engines, mainly due to how they are hardened.

most FD's die not because of natural low compression, but from other rather unnatural causes.
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Old 03-17-17, 10:37 PM
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Quote:
Originally Posted by RotaryEvolution View Post
what makes you think 4 injectors are better than 2? the FD rotor housings generally last the longest of all rotary engines, mainly due to how they are hardened.

most FD's die not because of natural low compression, but from other rather unnatural causes.
It's not that I think more injectors are inherently better, but that I think putting additional injectors in a different location could be beneficial. Putting injectors in the LIM would allow to oil to 'touch' more parts of the engine (which from what I understand seems to be one of the main arguments for premixing over OMP).
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Old 03-17-17, 10:53 PM
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that is partly true, but mostly for the early engines that had more localized wear.
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Old 03-18-17, 12:03 PM
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Quote:
Originally Posted by RotaryEvolution View Post
what makes you think 4 injectors are better than 2? the FD rotor housings generally last the longest of all rotary engines, mainly due to how they are hardened.

most FD's die not because of natural low compression, but from other rather unnatural causes.
RX8s have 2 oil injectors per rotor housing, then 3 in the series ll cars, and still suffer one of the worst chrome flaking on the housings of any rotary engine. The FD housings seem the most resilient. I recommend to leave the pump alone and supplement with premix.
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Old 03-18-17, 05:14 PM
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RX8s have 2 oil injectors per rotor housing, then 3 in the series ll cars, and still suffer one of the worst chrome flaking on the housings of any rotary engine. The FD housings seem the most resilient. I recommend to leave the pump alone and supplement with premix.
the RX8 engine has other inherent issues, the heat generated from the side port exhaust causes the side seals to wear exponentially, as well as transmit some of that wear to the edges of the apex seals that dig into the extremeties of the housings. the oil injectors using crankcase oil also ADD to localized wear, this can be seen in 2nd and 3rd gen engines by the wear line leading directly from the oil injection port on high mile engines. the use of 5W20 oil exacerbates that issue, as does not changing oil often enough.

i'm sure there is other underlying factors at play there too, perhaps the additional processes in treating the early MSP housings were abandoned due to saving costs, once they realized the mistake they may have brought it back along with the addition of 2 more injectors. at any rate the wear i describe can be found on most any rotary engine naturally but it takes a bit longer to develop on the FD housings.

in a nutshell, the RX8 example doesn't really compare. i also do not know why they place any injectors inside the engine, it seems counterproductive to placing them in the intake manifold where the oil definitely would lubricate the side seals. pre-1986 engines(exc GSL-SE) injected oil into the intake and those engines were some of the longest lasting, regardless of their heavy, chrome stripping 3mm seals.

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Old 03-19-17, 12:27 AM
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in a nutshell, the RX8 example doesn't really compare. i also do not know why they place any injectors inside the engine, it seems counterproductive to placing them in the intake manifold where the oil definitely would lubricate the side seals. pre-1986 engines(exc GSL-SE) injected oil into the intake and those engines were some of the longest lasting, regardless of their heavy, chrome stripping 3mm seals.
Yes! This is the exact reason I began considering additional OMP lines to the manifold in the first place!

It's reasonable to bring up the RX-8, but as RotaryEvolution said, the RX-8 oil injectors are highly localized in their distribution (just like on the FD), dripping oil directly onto the apex seals, regardless of if there are 2 or 3 injectors per housing.

I've been trying to think of why the oil injectors were pulled from the manifold on the FD in the first place... Could it have been emissions related? Or to meet some other goal valued above pure longevity? Thoughts on this?
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Old 03-19-17, 07:29 AM
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If you look at the literature on the OMP, Mazda thinks about it in terms of oil consumed vs apex seal temperature. I am inferring that Injecting directly on the housing has a better relationship of oil consumption vs Apex seal temperature.

I have diagrams of this, I'm just on an iPad right now and can't really pull them up.

The other main source of oil consumption in the rotary is oil leaking past the oil control rings and past the gas seals, because it is an old *** engine from the 60s with poor manufacturing and housings that tend to slightly warp. Mazda published papers on this recently based on an analysis of the 2009+ renesis engine.
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Old 03-19-17, 09:11 AM
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Quote:
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...I recommend to leave the pump alone and supplement with premix.
^This...even with synthetic engine oil.

Last edited by Sgtblue; 03-19-17 at 09:15 AM.
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Old 03-19-17, 11:43 AM
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If you look at the literature on the OMP, Mazda thinks about it in terms of oil consumed vs apex seal temperature. I am inferring that Injecting directly on the housing has a better relationship of oil consumption vs Apex seal temperature.

I have diagrams of this, I'm just on an iPad right now and can't really pull them up.
This is good info. It makes sense that injecting directly into the housings was best at accomplishing Mazda's singular goal of managing apex seal temps while minimizing oil consumption. The thing is, as end users we no longer have to compromise like an OEM. We can add an RA adaptor and independent oil feed, making oil consumption a non-issue. What would Mazda have done with the OMP if oil consumption no longer had to be considered?

PS I'd love to see that literature if you make it to a computer and it's are not too much trouble to pull up.


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^This...even with synthetic engine oil.
I think you are missing the point... My thought process is this: with premix, you are mixing oil with the fuel so the oil is ultimately injected into the engine through the LIM. In mixing directly with the fuel, you must also settle for 2 stroke oil getting a lot of places it doesn't need to be (i.e. the fuel tank, fuel lines, and fuel injectors, namely.) If you can introduce the oil in virtually the same location (LIM) and remove the fuel system from the equation, that seems like a worthy pursuit.

In concept alone, it seems to me that additional oil injectors placed in the LIM would be 'better' than stock, for the same reason [premix + stock OMP] is better than stock. The question then becomes: is [premix + stock OMP] better than the additional injectors? As with anything, there are pros and cons to each. With premix you would get better oil distribution, since the oil is atomized by the fuel injectors and injected in both the primary and secondary ports (this particular benefit being limited to when the secondary fuel injectors are operating, however). With the modded OMP, RA adaptor (and a good EMS) you would get much more accuracy and control over the oil injectors, and as a bonus you get much simpler operation, since you would just need to make sure a tank stays filled, not worry about mix ratios.
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Old 03-19-17, 12:18 PM
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Give me a few days for when I get back from travel. I emailed the author of the Renesis study and he sent me animations that show how the oil control rings have a natural gap with the housings (along the Z axis, think 3 dimensionally) where the oil escapes due to warpage in the irons. That's a main source of oil consumption, along with the seal gaps.

Then I have diagrams of the stock OMP control maps on the 2nd gen and oil consumption charts which I feel imply that the stock system is more than adequate for protection for most applications.

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Old 03-19-17, 06:09 PM
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Packaging, at least on the FD, is always a concern unless you're in love with removing stuff like PS, AC etc. and is especially true if you want or need to keep the stock stuff like intake, air pump etc. So while the RA adapter is a great idea, in practice it can be problematic for many.
AFAIK, in amounts considered reasonable two-cycle oil historically hasn't been a problem for pumps, filters and injectors. Unless that's not accurate, what your proposing by adding additional injectors in the LIM is fixing something that isn't broken.
The S6 OMP is, IIRC, RPM and load dependent. Not sure how adding additional injectors would effect that. Will it cause smoking under low load or idle?
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Old 03-19-17, 06:51 PM
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Old 03-19-17, 08:41 PM
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the oil is actually more beneficial to the fuel system than a hinderance. stuck injectors from sitting for prolonged periods or seized pumps is less likely, as well as rust inside the system.
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Old 03-20-17, 06:08 PM
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^This...even with synthetic engine oil.
We run Idemitsu or Rotella 15w40 which is a blend. Never had an issue with excessive wear or carbon and been doing this for 2 decades+
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Old 03-20-17, 07:35 PM
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Mercury injected oil in their high HP outboard motors.

continuousWave: Whaler: Reference: Mercury Oil Injection

I owned one on a bass boat and was going about 55 when the system failed. Ended up with 6 melted pistons.

It's a lot safer to just pre-mix. If you want added piece of mind, keep your OMP.
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Old 03-20-17, 11:49 PM
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Okay, I have repeatedly asked for this thread not to turn into another premix vs. OMP battle royale, yet that is exactly what it has become. I will accept blame for ever suggesting this modification could hold any benefit over the 'gold standard' premix... lesson learned.

If you are someone who does not mind premixing, that's great. But please understand I am not you, there are different things that matter to me.

I drive often, mostly the street. I don't always fill my tank, and I don't always run it to empty. I have no desire to make calculations while filling up.
I drive in New Jersey were gas stations are full serve by law. I do not enjoy awkward 'just squeeze this bottle in there' conversations with attendants.
I let other people drive my car and don't want a lesson in premix to be necessary beforehand.
I have space for a significant 2-stroke oil tank allowing at least 500 miles between filling.
I appreciate the security of having a low oil warning light, and the painlessness of topping off the tank in the garage when I get a chance.
I prefer to keep major engine systems separate so they can be controlled independently.

All of that, however, is completely irrelevant to this thread, so please do not comment on it.

I am trying to investigate an alternative to premix. For those of us wish do not want to premix, yet still want to improve lubrication. A separate 2 stroke oil feed is a good first step. What I have suggested is a potential step two. This is what I would like to discuss. Thanks.

Last edited by Oggy; 03-20-17 at 11:59 PM.
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