FC_fan

iTrader: (2)

Car: 1986 NA base model I guess (no stickers but has no rear wiper, 4 pot front brakes, 5 lug, no sunroof and black "lip" spoiler).
Car is daily driven and drifted every now and then (getting into that more)

So I was reading through some threads about OMP's and premix but they mostly refer to S5's and S6's. I think S4 OMP is mechanical instead of electrical like S5 and up right? Is that a better system less prone to failing?

another question, is it alright to premix in addition to the OMP? if so, would it be the same 1/2 oz daily driving, 1 oz spirited/racing per gallon of gas?

I searched this site for 30 min AND google searched this site but didn't find specific answers for S4's. thanks, I'm getting ready to start upgrading and rebuilding an S4 t2 hybrid, doing some homework. will be full premix when I get the t2 in and have EMS but until then I want to make this motor last as long as I can.

Ioncannon

They are both can fail however the mechanical one will wear down a slowly fail, giving you warning when to replace/repair/premix. The electric one can suddenly stop working, which could kill your engine.

FC_fan

iTrader: (2)

ok, so I'm in a better place with the S4 OMP. if it starts failing, would it be noticable on my oil pressure gauge? its the stock gauge.

and, can I just start premixing a little bit now with the OMP still operating? from what I have read on premixing, it oils the rotors better. my motor has 145k and I know while I have owned it, its been beat on quite a bit. I have only put on the last 15k miles. the car is all stock btw. thanks.

Napsterfreak15

The OMP is just as efficient as premixing.

The harder your are on a rotory engine the longer it will last because getting into the higher rpms helps reduce carbon build up.

https://www.rx7club.com/showthread.p...r+mazda&page=3

from aaron \/

What I am worried about is that the disadvantages of this mod don't seem to be mentioned. We have a lot of people going "premix" without knowing the consequences of doing so. I just want to clear things up.

What is wrong with the premix theories is that there doesn't seem to be any conclusive scientific proof that it is any better then the stock metering oil system. And by scientific I mean results that can be trusted. Not something like "I've been premixing for the past 30,000 and my engine looks new inside". I mean someone taking 6 engines, running each on a dyno under changing loads and temperatures, using pump gas. In other words, exactly the same use you would see on the street. 3 of these engines would use the stock MOP system, 3 would premix. This would go on for the equivelant of 150,000 miles. Each one would then be disassembled and examined. Then we can deal with facts.

Speaking of facts, I learned some interesting things talking to the owner of Atkin's Rotary (25+ years of experience...) in April:

Fact: the carbon on the rotors that most people attribute to the metering oil system is actually caused by bad gas, short starts, etc. Makes perfect sense to me. Now, you're going to wonder why there is a clean spot where the oil nozzle is. Simple really: that's where a drop of oil lands. The oil slickness prevents carbon from sticking.

Fact: most people don't understand the stock metering oil system. They are under the false impression that it is supposed to inject oil under pressure. This is exactly opposite of how it is designed. The system is designed for form a drop of oil at the injection hole. As the apex seal sweaps around, it catches the drop which then flattens out along the seal. Thus, the apex seal is lubricated throughout it's travel. Oil is applied exactly where it is needed...Which brings us to:

Fact: premix lubricates the face of the rotor. This is wonderful, but what we really need is an oil film on the housings...Why doesn't this form with premix? Well, because it is designed to burn. It is, after all, meant to be used in two cycle engines. In the 2 stroke, the surfaces the oil is lubricating are not exposed to combustion. In a rotary, the exact opposite is true. The premix very easily burns off the housing. This, no firm forms. Since standard crankcase oil is higher in viscosity and much harder to burn, the apex seal leaves a nice slick film on the housings, exactly where it is needed.

Fact: Premix will more quickly clog injectors and foul plugs then the stock metering system. This is probably not a big deal for most of us here. Also, to much will clog exhausts, smell bad, cause smoking, etc. Again, probably not a concern here. Just something to be aware of.

Question: If premix is so good, why did Mazda not design the metering oil system to inject directly into the fuel line before the injector?

Premix is great when used in racing engines that are constantly >8000 RPM where the stock system cannot cope, but for street driven cars, it is my opinion that the stock system is more then adaquate.
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Napsterfreak15

That is false. Even if the electric one fails it will still work at 20% efficiency due to suction.

I ran my 7 for a year with out an omp/not premixing and i still have good compression. not having a working omp just wears out your engine faster but I highly doubt it will kill your engine right away.

FC_fan

iTrader: (2)

wtf? how did I not get that thread come up in my searches napster!

thats some good info there but I think (after reading some more threads) that premixing AND using the pump is the best of both worlds since 2 stroke is designed to be burned up. someone stated that it does oil up the surface of the rotor as well which helps carbon to not stick as easily. it looks like the OMP is only concentrating on oiling the apex seal and outside of the housing. I know oil gets into the rotor too but the sides of the rotor don't seem to be getting oiled as well and hence you get carbon build up on them a little bit.

I don't really see the harm in using both methods since the 2 stroke burns anyway a little. does that make sense? just basing this off a few threads I read on premixing. given that my engine (as far as I know) has 145k and never been rebuilt, the carbon is probably already there but my engines running fine so adding premix would be preventative maintenance. thats assuming the things I read were true (there were people with 25+ years rotary experience posting so....). thanks for the help, the search feature on the site isn't great, but I can't believe that my google search of the site didn't bring up some better threads.

EDIT: actually, if running both OMP and premix, would it be too much oil and run any different???

Napsterfreak15

Just also add Aaron cake to the "search by user name" field