Premix 101: How it works
 

I have read dozens of premix threads over the years here at the club, and probably another 100 all over the net. one simple question that has never been asked (that i know of) is "How the fuck does it work". For me, I have the yearning to know how everything works. When I was a child, I was always in trouble because I'd take things apart to figure them out. If you, are like me, this little article is for you...

Gasoline is volatile, Oil is not. This little tidbit of info is important, and you'll read why.

Premix, as a concept is very simple, whether it be in our wankels or 2 stroke piston engines.

When gasoline vaporizes, the oil in it separates since the oil is not volatile like the gasoline. So, injector shoots fuel, fuel vaporizes and the oil seperates from the gasoline it was mixed with.

What happens to it and where does it go?

The oil then forms a mist of droplets, which gets flung around by the flow of air in the engine. This means this mist coats everything with a fine layer of oil. This is great for our engines, as the piddly drippings of the oil metering pump are relying on the apex seals to drag oil around the housing. Ever taken apart a motor that has never been premixed? If you have, you should have noticed where the oil was going and where it wasn't. You'll notice a nice smooth line emitting from the oil injector port area, and it expands toward the combustion side of the housing. Everywhere else is all worn. That shiny line that magically expands toward the combustion side of the housing is the path of the injected oil being dragged by the apex seal. Obviously, this not ideal, the whole surface needs to be as wear free as possible!

This is where premix is desireable. OMP or no OMP, you want that oil in every nook and cranny of the housings surface and seals. This is why premix is far superior to an oil injection system. The mist of oil gets tossed onto everything as it fall out of suspension from the gasoline, whereas the OMP drips oil and needs the apex seal to drag it across the housings surface.

It is my belief, although many will debate this, that a working OMP and premix is the best of both worlds. A)You have some redundancy in lubrication and B) You are still lubricated by the OMP during engine braking when the injectors are off.

I hope this little article explains exactly how premix works, and why it's such a great thing. Attached are photos of a 160k rotor housing that never saw premix in its life, that demonstrates what I was talking about with the OMP and its ineffectiveness.

Using the omp you're using oil that gets dirtier over time, which is bad.

The injectors are always on pushing out fuel, the car can't run without gas it just uses much less during idle.

Please don't muck this informative thread with misinformation like that.

And it is also apparent that you didnt comprehend part of it as well.

What I'd like to see in this thread is tear down photos of a fully premixed engine, as all I have is no premix, OMP damaged housings.

Just stop posting.

Nice! Good stuff! Never really pondered into the... chemical dynamics? Of it. That's really interesting.

And I, too, take many things apart solely for the knowledge ;)

How about you all stop acting like you know everything when you know nothing and obviously are the ones with mis information.

1) its simple a car uses gas when it idles, it doesn't run on only air its not a human being its a machine.

2) oil that's circulated throughout the engine is getting older over time, pre mix goes in clean and is never old oil that's been run through the engine.

3) when you downshift and the rpms rise no you aren't using anymore gas , isn't that common sense since you aren't hitting the gas pedal... This isn't rocket science

4) stop talking to me in threads if its only to act like this is high school, I'm 30 years old and I'm here for knowledge not drama.

No one mentioned idle. He mentioned deceleration.. at which in alot of situations there is no fuel being injected.

Even on deceleration the air/fuel mixture goes rich, therefore there is unburnt gas still in the chamber. This is what causes backfire

What!?

When engine braking above say 2,000 rpm the ECU injects NO fuel at all when your foot is off the throttle.

So you assume there's no gas still going through the engine.

How do you think it stays running?

By the momentum of the car rotating the wheels, diff, transmission and the engine.


Edit: I have a wideband that confirms this, when I am coasting down a hill while in gear it reads full lean.

Premix is always lubing the engine. On decel, you know how the engine braps out a lot? That's called excess fuel pushing through the engine igniting without load, hense the fireballs and flames.

Therefore gas is still going through the engine.

Upon deceleration, the supply of air to the engine is reduced (due to the throttle plates closing). If the fuel supply was to remain unchanged, the air fuel mixture would become rich. This is not desired since a rich fuel mixture increases gas consumption and harmful emissions. It also causes backfiring in the exhaust because not all the fuel is burnt in the engine, as it should be in normal conditions

Type in "lean deceleration" into google.

Most if not all Fuel injected cars go into fuel cut on deceleration until they reach idling RPM to save on gas and cut down on emissions.

O......M......F......G...... WTF is he babbling about?

Misinformation is the most dangerous kind of information! "Someone" needs to just toss a scan tool on any newer car and watch injector PW, or put an Oscilloscope on an injector driver...hell even a Duty Cycle % setting on a typical multimeter will show it...but virtually everything, since electronic fuel injection, has <b> ALL </b> fuel shut off under decel until a preset minimum RPM threshold for idle maps to kick in. Therefore...as said before, when under deceleration and using only premix, no oil will be injected as the fuel injectors will be inactive

I just build shit and drive it.(screw the graphs,etc!).Slap shit on and go.
..But I understand the No fuel on Decel.I actually read that a couple times in Various thread,so No Argument from me about that!

I just wanted to toss this out for pondering.

My 2 cents is:If you are using Premix,that momentary length of time Decelerating should NOT have anything to do with any EXCESSIVE wear,as it is Momentary and If the car is properly Premixed then it should have enough Lubrication to keep it lubed until it gets Premixed fuel when you hit the Throttle again.

May not have anything to do with pics of housings but from a "simpler" point of view,it seems about right..doesn't it?

Since this is the "Premix 101" thread, it would be nice if it included some ratios and types of premix oil to use. I'm not going to clutter it in case I have some misinformation.

Agreed

I personally use Amsoil Saber outboard 2 stroke premix by itself... no OMP operating. Depending on what im doing, I mix a ratio between 1-1.5oz oil/gallon on gas

:Kill2:Why the fuck...


are PEOPLE MAD?!

wthdidusay82, you have no idea what your talking about.

I think he does lol. I don't cut fuel on decel my wideband reads full rich on decel.

Yea, you can do that on a standalone but stock ECU cuts off injectors on decel.
If you're worried about injectors cutting off, put in neutral when coming to a stop or coasting down.

wthdidusay82 : Dude...you are over thinking things.

Don't worry about what brand or whether to keep the OMP with premix.
Just disable the thing and run TCW3 .

You are right though, clean oil is important but if you are using OMP and premix, you are still getting carbon buildup . The whole purpose is to rid of carbon on rotors and clean housings.

Never seen a non functional OMP damage but I would think it would be severe.
OMP only housing looks like that in the photos. You see the clean streak where the oil seeps out. Or several clean streaks . The premix only housing after 60,000 miles were clean, no streaks no wear...just clean.

One engine was using synthetic with OMP. That made a mess since it didn't burn completely off.
The engine using Mobil1 0/40 from rebuild and 1oz/ gal premix showed no wear, no streaks..nothing. All the components lubed by oil were very clean.

Some of you can say what you want but from 2 different engine break downs, it was a difference.

Exactly

I got a TII on premix with a T04 and 1000/2000.
I have been using about 12 oz per tank,which is less than the "normal" 1oz to One Gallon of gas.
Now this is on Haltech.
I had it on the RTEK 2.1 and tuned and it fouled the trailings.Maybe over-premixed.
(got Trailing coil error)Hence going Haltech.
I just had enough of the stock wiring and crap associated with 20 year plus old stuff.
..
JJ..not mad...heh,heh..but I am a little "coo-coo for cocoa puffs" at times!

A stock fc ecu reading an sensors that are properly set (ie, 1k ohm tps at idle, etc) goes FULL LEAN on decel. So there's zero lube on decel from a premix engine aside from residual oil, and an omp engine is seeing idle condition oil injection as it reads the throttle position not engine speed (s4 ref.)

There may not be decel fuel cut if your conditions vary from this any (different, aftermarket ecu and not using decel fuel cut, or a stock computer w sensors not set to fsm specs.)

Every day is April 20. :weedpoke:

If the lemans 787b ran with only premixfor 24 hours straight its a testament showing only premix and no omp is perfectly fine. Lots of rx7 owners pre mix without the omp and never have problems.

I don't smoke that stuff, quit a long time ago.

Running 1:1 Premix. No OMP. Motor Has 2000 miles on it. So it will be awhile before I
take it apart. But she runs great.

I can see how you'd form a hypothesis from this but really, two engine teardowns is hardly enough data to come to a conclusion.

I didn't post ratio's because that has been beaten to death already, and I didn't want this thread to decend into a debate.

Alas, not only did it decend into debate, first reply is loaded with misinformation.

Sorry man.

I admit there are some valid points that you've contributed, there is no right or wrong, and no matter where you go people will argue their point of view.

That said do what you're most comfortable with, we all know using only the omp and no pre mix at all is the worst option.

I didn't suggest just running the OMP by itself, this thread was intended to...

A)Explain exactly HOW premix lubricates and the science behind it and...

B)How awful it is to just run with the OMP without premix.

Those housings pictured are my own housings from when I rebuild a 160k mile engine that never saw premix. That engine was original when I took it apart, it even had asbestos gaskets in it!

Working OMP or not, premix your engine, it'll love you for it

As mistery stated, not all of the premix burns off, so you'll have some left during decel. I just personally prefer having the OMP still for that situation. The reason i know this is because I rebuilt a homelite leaf blower last month for my mom, and when i crank it up and tested it, a little oil would make it out of the exhaust port.

I know you didn't say to use it by itself , I was just stating that as general knowledge.

I never pre mixed my first rx7, now I've realized how much I was missing out on.

Before I was all paranoid thinking it'd clog my fuel pump, injectors, and fuel filter.

Now after seeing how many people do it with positive results I have no reason not to do it.

You know, intellectually I can buy into this proposition without qualm but then I'm left contemplating my (nearly) 250k bone stock engine that has somehow managed to survive 24 years on "the worst option".
Is my experience the outlier here?

I doubt your engine has never been rebuilt or replaced. I'm saying 99% chance it has been rebuilt/replaced.

That said, the stock omp works yes it does but there are better options.

https://upload.wikimedia.org/wikiped...Engine_ani.gif

The fuel/air charge in a 2 stroke engine lubricates the crank case as well as the cylinder and in most cases are mixed at around 40:1 (3.2 oz per gal) which is relatively high compared to what most will run in their rotary at about 100:1 (1 oz per gal).

FC3S Pro v2.0:&nbsp FAQ - Pre-mix

^ a good read.

Idemitsu Lube Spec sheet
http://www.ilacorp.com/images/web_premix.pdf

Idk why they fail to say use .5 oz/gallon if you have a working omp and 1oz/gallon without

Good stuff, thanks for the info. I run premix with no OMP and was always a little worried about the premix.

Yea ... but shows what omp and premix does to internals.
Not scientific , but enough .

You'll be fine, many of the hardcore rotary enthusiasts premix with no omp.

Just one thing I've read/heard but didn't see mentioned in here, fuel cuts on decel, but two cycle oil is designed to 1) burn off cleaner and easier that four cycle oil(less gunk) and 2) leaves behind a "dry residue coating" that lubes between/during cycles.

Being that rotaries are known for running rich I would assume more "dry residue" is left behind than needed, that leftover would lube your engine on decel. Again assuming your on the gas more than not(which you should be if your piloting an rx7 anyway ; ] ).

Stupid question, but I want to ask anyway. You can start using premix anytime right? Like there's nothing wrong with my 112,000km stock engine going from never using premix to using it suddenly. The wear that's already on the housings will always be there, but it'll help with wear from this point on, correct?

Do you guys measure how much you're putting in and how do you put it into the tank after you've measured? I still have my OMP and I'm Canadian so I'd estimate one oz/30ml every 4 liters of gas (a little over 1 gallon). This seems like a PITA since I always put in different amounts, I almost never fill up, 20$ here, 10$ here, etc. Would it still be worth it even if I plan on swapping the engine once I have the money(probably next summer)

That is why I carry the small bottles.(approx 3oz).
Each bottle does about 20 buck in gas.(Canadian)
If you want to stick with the ONE to ONE ration then use your noodle..Get the math book out Schroeder and convert it!...(chuckle..youngsters..lol!)
I'm stickin with my bottles per 1/4's..(that is about 12 oz per tank on an s4).
It beats having to look at a big bottle and go Pour..nope,not enough,glug..nope..GLUG..ah shit!

I don't think it can be too late to start premixing. It can only help unless you over mix or something.
I usually look at how much I have in the bottle and guess how much gas I'll need...pour in 10oz of idemitsu and then fill up about 10gal of gas that's good enough for me...

Be careful to use only premix oils of the twc3 type as they are the ones we would use. Or unless it says for rotary use (like idemitsu)

@ryan hey bro 100:1 without an omp so thatd be 100mm for every 10litres. I'm assuming the 2stroke 1litre bottles will be marked in 100mm increments up the side of the bottle like ours are so pour and check like mysterstyx says. I carry a funnel and rag in the back.So you just have to work out how much every 10litres of fuel costs and ask for gas in strange dollar amounts. It really weirds out the gas station attendants :) Can't remember the with omp ratio. 400:1

Sent from my GT-I9100 using RX7Club

Doing it without it pre measured is like mixing lets say vodka with orange juice, there's a 1/3 chance of getting the correct ratio.

Sometimes it'll come out strong and you'll have to add more orange juice, sometimes it'll come out weak and youll need to add more vodka, then sometimes it will come out perfect. When making drinks you can drink it to see if its right or not, obviously there's no way to test your gas after pre mixing and pumping in your gas (that I know of).

this is the factory metering pump test data, and the S4 vs S5 metering pump maps.

reading this thread is gonna make me add more Vodka..to anything..