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