FD3Smaniac

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i just recently purchased my first rx7 and have not really seen premixing before lately, and i was wondering what are the advantages in premix?

Turbo II Rotor

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Search.

Turbo II Rotor

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https://www.rx7club.com/2nd-gen-archive-72/omp-pre-mix-mod-write-up-436722/page4/

read this from start to finish.

Aaron Cake

iTrader: (1)

Advantages:
-some say it lubricates better. There's no direct evidence of this, only anecdotal evidence. Also kind of pointless to suddenly switch to premix on an old engine that has spent it's entire life running with the metering oil pump

-cheap alternative if metering oil pump fails

Disadvantages:
-might not lubricate any better
-pain in the ***
-adds to cost of fillup
-could have trouble passing emissions if premixing
-must mod the engine to support premix (removed and block off stock metering oil stuff)

NZConvertible

This point needs to be made more often. The supposed benefits of pre-mixing would only apply to new or recently rebuilt engines. The number of people pointlessly converting old engines baffles me.

Rx7TyreBurna

iTrader: (1)

Heh, I am premixing now.

It is different.... I got a rubbermaid drink holder, and it is 16 oz. It has markings for 12 oz, and other measurements, but I fill it up to the 12 and keep it in the car for when I am going to fill.

I only carry 12 because I usually only put 11-12 gallons of gas.

Advantages would be... for me, my vacuum spider was broken, and the air bleed lines going to the oil injectors. Also, my oil lines were looking really bad.

So, instead of spending a ton of money to fix all that, I just bought a block off for the OMP and some bolts to cover the oil injector holes, and then some 2 cycle oil from walmart for super cheap.

I have heard that one advantage of premix is that the 2 cycle oil contains less ash? Not 100% sure about that though.

I could see one disadvantage. One being that you are adding oil to your gas. This oil is running through your filter and then through your injectors. I know that oil is thicker then the fuel, so I am not sure how well the injectors will handle it. I am still waiting to see if it makes my filter, pump or injectors fail earlier.

GL!

antnicuk

what about if you are running double the power than the stock car, can the stock omp keep up?

the theory overhere in the uk at the moment is that if you have a big power engine, then premix is the way forward for longer life

NZConvertible

The vac spider is ~US40 from Mazdatrix, and the oil lines can be replaced with small engine fuel line for ~$10. You will quickly go past that $50 with the increased cost of premixing. So not good economics really.

That's a complete non-issue. The mixture is so weak it would make absolutely no difference to the filters, pump or injectors.

KNONFS

iTrader: (14)

Less carbon buildup?

Aaron Cake

iTrader: (1)

The only premixed engines I've torn down have been low mileage engines that failed some other way. I've seen no difference at that point between premix and metering oil engines of the same mileage.

In my opinion (based on experience) carbon buildup is more a function of how the car is driven then premix vs. metering oil pump. Others will undoubtedly disagree.

Rx7TyreBurna

iTrader: (1)

I agree, premix is going to cost more in the end. I am sure that the $5 i spend to buy the gallon is going to cost more after a while. But, other factors I guess I didn't mention.

One being that I considered that with the OMP, it injects oil into the engine over time, and therefore I am going to have to put at most 1/2 a quart before my next change. That isn't a lot, considering a quart of oil is $3.40 for some valvoline 20/50. But, it is still costing me a little, must keep checking the oil every time I fill the car with gas and make sure oil level is still good. I do this with most cars anyways, I think it is good practice.

Another reason I switched to premix was the addition of S5 IIM and UIM. I know it wouldn't have taken much to bend the rod around the manifold, but I decided I didn't want to. I also wanted to clean the engine bay up a little, which is why I removed my "emissions". Not for power, or efficiency, but cleaner engine bay.

I think if your OMP stuff is all working just fine, there is no point in removing it. Or if you aren't sure if you should remove it or not. Just keep it.

NZConvertible

IIRC, premixing uses about twice the volume of oil the OMP does, plus the oil itself is more expensive than regular oil.

Personally I don't get this. I drive my car a lot more than I look at the engine, so functionality is more important. But that's just me...

hondahater

iTrader: (2)

this is interesting and some how I never really looked at it that way. What do you guys think about this (nzconvertable and aaron cake). The mop while being tested and designed for x amound of horsepower has never really been tested (in a mazda facility) for anything much over stock I'm sure. I know the mop works off of rpm only but couldn't the added friction, heat and, pressure (if turbo charged) of the added horsepower warrant a need for more lubrication? Just a thought.

I premix and always will because I like the consistancy of lubrication (more gas needed more lubrication available) and after my tear down I was supprised to see how clean it was in there compared to what it should have looked like.

edit: maybe something we should look at is what mazda does with thier race engines. Do they keep the mop or do they toss it in favor of premix?

NZConvertible

Interesting point, but (tentatively) I don't think so. Friction is a result of the engine speed, so unless you're increasing redline (not always necessary on a turbo'd engine), friction should be the same. Increased heat may well negatively affect the injected oil, but I can't see increased chamber pressure having any effect.

What "should" it have looked like? The problem with the whole debate is that rarely do you ever see two engines, one with the OMP and one always pre-mixed, that have been torn down after enduring similar conditions. Like Aaron said, the evidence is anecdotal only.

Racecars will rightly use premix purely for simplicity and reliability. Road cars are very different, so the comparison isn't necessarily valid. Race use doesn't always imply "better", just different requirements.

I've got a photo of an R26B out of the 1990 787 (the predecessor to the 1991 787B). It has what looks exactly like an OMP and oil lines bolted to the side of it. It might be something completely different, but the resemblance is hard to miss. It also looks like the fuel rail had an OEM-style PD on the end of it, but that's another debate...

hondahater

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Thanks for the reply and your input. I was going to say this in my last post but desided not to. I'm building my car for a 1/4 mile dragster so when I think in terms of anything rotary now I'm thinking what is best suited for 500+ rwhp. This is why I was wondering what mazda did with thier race engines (and absolutely you are correct that race use does not imply better, but if they use it then it must work). I don't really agree with ripping out the perfectly good mop if someone is stock just because the debatable point of a cleaner motor. I've always thought the mop was a bit archaic and crude. I'm not saying it doesn't work as very obviously it has and for a long time as there are still stock n/a's out there with the original motor in them witch has to say something however I just don't think I trust it with high horsepower applications. when you can have such an even mixture of lubrication in your gas as compared to little oil droplets on the face of a rotor it just kind of makes sence if you think about it.

The reason I thought my motor was cleaner than what it should on breakdown is because I had just cleaned everything and rebuilt that motor 3 or 4k miles before I had to rerebuild the motor due to a side seal issue that caused lots of blow by. Maybe it was to soon to draw any conclusions but the rotor faces where very clean and had no signs of starting any carbon build up where you usually find it the most with mop equiped cars.

I just have a tendency to think that mazda didn't test the car on 30psi of boost (of course not the stock turbo charged rotary only saw between 5-8psi, they really have no reason to test over that). That being said I feel a less crude way of lubricating your rotors needs to be done for reliability.

deadRX7Conv

The issue I have is that noone knows how well their oil injectors are working. Anyone ever take them out and test 'em?

Premix doesn't cost anymore then burning oil. It all depends on how much and what brand that you use. Gallon jug of 2-cycle costs the same as gallon jug of motor oil around here.

I think that Mazda's OMP is a compromise at best. What makes anyone think that their oil injector rates are for maximum power or engine longevity?
Emissions and consumer ease of ownership are taken into consideration. I think the RX8 engine longevity snafu is proof of that.
There are just too many sacrifices or compromises made on the OEM level.

Also, IMO, most of the carbon issues in the rotary isn't from the oil. Its from running rich because of poor tuning. I doubt anyone will argue that you can't beat OEM FI tuning. So, what makes you think that you can't beat the OEM oil injection, or OEM turbo, or OEM brake,s or OEM exhaust, or OEM HP or............?

I guess that ever mod done can seem anecdotal to someone.

SirCygnus

iTrader: (1)

i woudl say its personal taste.

NZConvertible

Premixing has been around for far longer than the OMP system (think 2-strokes), so by definition it's far more archaic. It's also cruder in the sense that you have to use more oil to compensate for the fact that not all of the premixed oil provides lubrication. So whatever your opinion of it, you certainly can't describe the OMP as archaic and crude when comparing it to premixing.

Really? What use is oil sitting on the face of the rotor? Let's remember one important fact: oil suspended in the air/fuel mix isn't lubricating anything. You're relying entirely on enough of the mixture hitting the chamber walls to provide sufficient lubrication. Oil that lands on the rotor face or goes straight out the exhaust without hitting anything is completely wasted. On the other hand all of the oil applied directly to the moving surfaces is used for lubrication. Think about it this way. If you were going to lubricate (say) a door hinge, would you spray a fine mist of oil all over the hinge and part of the door and frame, or would you apply a few drops of oil directly to where the moving surfaces rub over each other?

Look at the progress of Mazda's OMP designs. First oil was injected directly into the intake airstream at the carb (1st Gen). Then they moved to a system where some oil is injected into the intake and some is applied directly to the apex seals (FC). Then they removed the intake nozzles and applied all of the oil directly to the apex seals (FD). Then they added a second nozzle to apply oil to the apex seals (RX-8), presumably to distribute the oil more evenly over the length of the seal. So Mazda's method of getting oil into the chambers has steadily moved from a premix-like method to direct application. I think that if introducing the oil with the air/fuel mix was the best method, Mazda would have stuck with that method and advanced the design rather than abandoning it.

Not that I'm saying that premix had anything to do with this, but I seem to hear about premixed engines being torn down early (hence the clean engine comments), and yet engine longevity is the main advantage claimed. Just an observation. Where are the 100,000+mile premixed engines? That would be a much better comparison.

You're right, it was far too soon to draw any meaningful conclusion or make any claims of superiority. It's not a valid comparison at all.

This is a very good point. Apart from the FSM test, the only way to know if it's working is to monitor oil consumption.

I don't know what you're using, but the quality synthetic 2-stroke oils everyone harps on about cost a lot more than the Castrol GTX Protec I use...

What makes you think they aren't? The SAE paper I referred to shows that minimum wear at full load was exactly what the system was designed for.

Do the RX-8's problems have anything to do with the OMP system? I don't keep up with RX-8 stuff. If they do, what's the issue? If not, they shouldn't really be part of this discussion.

I totally agree that the fuel probably plays a far greater part in the carbon build-up than the oil does, but it's not "poor" tuning. It's tuning appropriate to the manufacturers need's and is typical given the technology of the time. The amount if time even the best aftermarket tuners would spend tuning one car would only be a tiny fraction of the man-hours a manufacturer would spend on tuning one production model's EFI.

I don't believe I've ever heard someone say that. Manufacturers have a totally different set of requirements they have to meet compared to the average car modifier, not least of which is keeping the engine alive under wildly varying and completely unpredictable conditions. Until recently, stock mixtures in any car tended to be very rich because that keeps abused engines going. These days they tend to use the electronic throttle and/or lots of ignition retard to do the same thing.

Go look up anecdotal in the dictionary. It doesn't mean what you think it does.

RotaMan99

Just my opinion,

2 stroke overall has a lower flash point the motor oil. So the 2 stroke would burn off before the motor oil would. Some 2 stroke oils have additives which make them, so called, ashless. Im guessing this would let them burn cleaner then motor oil which is not designed to burn clean and has a higher flash point which I would think would leave more carbon deposits? Also, since motor oil doesn't burn as quickly, it could possibly lubricate better, which would mean you could use less then the amount of 2 stroke you would need to do the same job? Now, by the time the combustion temps get high enough to burn off the oil, that face would be only milliseconds away from being lubricated again.

Remember, just my opinion, if wrong let me know, same as below.

When your dripping oil with the OMP, its not just landing on the rotor face or just the apex seals or anything else. Its being atomized by the intake air and possibly the heat in the engine which will allow the oil to go all over everything. Same goes for 2 stroke in the fuel.

imloggedin

i got my car about a month ago and was removing emissions last night and one of the oil lines was disconnected for one of the injectors. all of them were very brittle. i opted to replace the lines and clean it all up instead of premixing because of the pain it would be to premix every tank. but i cant say ive had much luck with the whole OMP setup in the past. like previous posts said. how do you really know if its working or not unless its not using oil (and when is it too late)?

ericgrau

iTrader: (1)

I'm going to get the adaptor from Rotary Aviation that lets you keep the OMP, yet while feeding it 2-stroke oil from a seperate tank instead of using motor oil. ~$80, I think. I don't have the link at the moment, try googling it or searching these forums.

I might also mix just a little bit into the gasoline on top of that, or I might get lazy.