Ok, so I have caught the 'bug' so to say, and bought my buddy's '87 n/a RX7. He has been explaining the workings and maintenance to me. He explained that it burns oil, but never mentioned anything about adding 2-cycle oil to the gas as I'm seeing a lot of members on here doing. Am I missing something, or should I be doing that? What kind do you use, how much, and why? I'm new at this whole thing and would appreciate the insight. Thanks in advance.

 

Welcome aboard.

You have an S4 model that has a pretty reliable mechanical oil metering pump (OMP)...
Later models have a potentially failure prone electronic OMP.

Both systems feed oil from your sump (Your regular engine oil) into the combustion chamber.

Typical engine oil isn't the cleanest burning stuff and leaves a bit of carbon. Some people like that the 2-stroke oil burns cleaner.

Some people remove the OMP and block off the hole it leaves, they run ONLY 2-stroke. (Not sure if this has been done on your car.)



It adds a little extra lubrication to the apex seals and promotes longevity. However it's not 100% necessary if your car has a functioning OMP.

 

thats a debate here but i wouldnt recommend it. ive seen some injectors clog because of over premixing. i guess the whole premixing thing comes from people taking apart their engines and seeing the clean point left in the rotor face apart from all the other carbon buildup. still on a stock n/a i wouldnt recommend it
fixed

 

Welcome! I hope you enjoy "the bug".

I drove my car for a couple years with the omp and it wasn't half bad. It definitely works well when it's hooked up properly. I had a friend that had a 84 GSL-SE, and I bought his engine from him and ended up putting it in my car.

I always wondered why his car never really burned hardly any oil. During the partial disassembly of his engine, I found out that the vacuum line that went to the oil injectors was disconnected from the intake manifold all together.

I have a vague understanding as to how the oil injectors work, but I know exactly how fuel injectors work. To me, knowing that every time my fuel injectors open, they are dumping in the proper amount of fuel and oil is somewhat comforting. This basically means that whenever my engine is running, I know for a fact that it's gas seals are being properly oiled.

But to answer your question, you don't have to run premix in a car with a functional oil metering/oil injection system.

 

Premix is not what everyone makes it out to be. For one it’s a pain in the ***. Second, you DO NOT get the consistency the OMP gives you. Another down side is that the 2 stroke oil you would use in the tank can clog up your fuel system ( Injectors, filter).

I would not recommend Premixing with an OMP (too much oil) OR without one. I would suggest that you keep it in (in case you were thinking of ditching it for pre mixing)

I’m sure this will cause a debate that many people will get pissed off about, but that’s my opinion and why I trust the OMP over pre mixing
.

 

You make a compelling argument. I've actually considered rebuilding my OMP and going back to it, but for now I'm content with putting 2 stroke oil (I actually use TCW3) in the gas.

It's really a matter of personal preference. I liked having the functional OMP, but I didn't like having to open the hood and add oil so often. (In all fairness that old engine probably had bad oil seals though.)

Have you ever tried using two stroke oil though? It's not that much of a pain in the ***... Just put oil in before you fill up. Sure you have to do a bit of calculation, but that's good for your brain. (The smoke probably isn't though)

About consistency. This is where the debate comes in. I wish someone would fix this, so please correct me if I'm wrong. I was under the impression that 1.28 ounces to 1 gallon of fuel was the ratio that would exceed the minimum/maximum of oil that the stock (unmodified) OMP puts in the engine. In other words, I was told that using two stroke oil in the gas was considered "safe," regardless of any consistency issues.

I'm not ******* on you, or disagreeing with you. I just want to get it straight, so again, correct me if I'm wrong.

Logic tells me that like you said, the OMP would be more consistent.

 

the OMP might deliver it more consistently, but that isn't where it falls short, it falls short in uniform delivery. don't confuse the two. that's where having it injected with the fuel is particularly advantageous because it goes everywhere the intake charge goes, which is figuratively splattered all over the insides of the motor. the other issue is that injecting dirty motor oil is, well, dirty.

 

If its a stock engine I wouldn't mess with the oil system as it works fine.
I think there are some advantages on premixing though, for one, you can use an oil which is better suitable for this kind of lubrication (2 cycle oil is different from regular motor oil), so it should lubricate better and burn cleaner. The oil is also a lot cleaner, because it's never been used before. As for clogging up I don't think this is a problem, a lot of 2stroke bikes and snowmobiles premix their gasoline, with a mixture of as much as 1 : 25, and don't have problems with clogging up. But it is less convenient, and not needed on a stock engine.

 

I have been running a 128:1 ratio for years. How could it not be as consistent as the OMP? When I fill up I do a little math and I make it come out to the same premix ratio every time, one ounce oil to one gal gas. The more gas I use means the more 2 stroke oil I use. Do you know exactly how much you OMP is adding? I went through two oil metering pumps before I learned how much more consistent premixing is, and I had to wait for rtek to come out so I could get away from the s5 OMP.

 

hers some basics about oil and gasoline
gasoline dilutes oil making its lubrication properties inadequet for proper lubrication
oils lublicates best when hot
so assuming that 2 cycle oil has these similar properties when its premixed its diluted and comes in cold so it wont provide maximum lubrication (correct me if im wrong)
this is my theory and why i dont recommend premixing
oil pumps are designed to work with the engines they are placed in (but thats my opinion i just believe that engineers made the system work the way it does for a reason)
and clogging is usually the result of too much oil in the fuel system.
just like when gasoline sits out too long it creates a oily substance that can clog the f/p injectors and even fuel rail oh and the fuel filter.

 

Check the 2nd gen Archives for a long discussion on premix from years and years ago, where this has all been hashed out before.

 

Aaron Cake is right, that is a good read. I’m shocked on the amount of openness of this debate, no bashing and just conversation, this is how we better ourselves with knowledge.

I did forget another option, OMP adapter, that is what I will be running along with an S4 mechanical pump / front cover. This will let you keep the stock S4 pump and put clean two stroke oil into your motor. I’m currently working on a kit, I hope I will be able to offer it on this site soon.

 

https://www.rx7club.com/showthread.p...&highlight=OMP

 

I apreceate all the info and am loading the link as i type this and will be doing alot of reading about this tonight thanks everyone

 

The thing to remember though is that the only one who has done actual scientific testing is Mazda. We all speak, but it is just anecdotal.

 

^

Keep in mind, Mazda also had to deal with the average Joe who didn't know what was under the hood and only cared if it came in pretty colors...

Mazda had to deal with the EPA, DOT, and other government oversight organizations...

 

Early rotary engines (carbed models) injected engine oil into the fuel mixture at the carb, thus feeding the engine a fuel oil mixture. The reason for the OMP was to meter the oil more precisely to the engine needs and to reduce overall consumption. Beginning with the fuel injected engines, it became necessary to devise a new way to add oil to the combustion chamber. Since the gas was injected there was no carb for the oil and gas to mix before it was drawn into the engine.