13b N/a ?....

[Dominic]

Not sure whether I agree with the statement that pre-mix runs the correct ratio 100% of the time, in fact I think there are cases where this could be the opposite. E.g. for your example.... If you blast the car then drop down off the revs approaching lights, as the car is decelerating, with pre-mix, very little oil will be entering the chambers as the throttle will be almost closed....... combustion in the chambers will still be occurring however, therefore during the slow down/coast period, the engine wont be getting much oil. With OMP, as the car comes down off the throttle, even though the throttle is closed the OMP will still inject oil into the chambers because the OMP pump is governed by rpm not throttle position, therefore the engine’s lubricating demands are still met during this period

if combustion still occurrs...there must be fuel.....if theres fuel theres oil. there is also residual oil from previous induced strokes.  The retardation of ignition timing increases unburned fuels, thus, \'unused\' oil. I think in reality there is very little practical difference in this scenario

Steve

Probably should re-word the bit I wrote about combustion occuring on overrun when the throttle is closed as its not really relevent and may not even be the case on injected cars. The point of the fact is the rotors are still spinning on overrun, therefore wear is occurring and as metalhead pointed out, only a very small amount of fuel will be entering the rotor chambers on a carbed car and even less/none on a fuel injected car so surely then an OMP system offers better lubrication in this scenario.

At the end of the day its all gonna boil down to personal preference, experience, and the motor in question. Interseting discussion though and I\'m still unclear as to which oil set-ups are \'best\' for different applications :chat

Here\'s a couple more things to throw in the pot:

Did the 787b run pre-mix or OMP?
Or how about the Daytona/IMSA rotaries in the USA?
I\'ve seen pics of IDA fed race rotaries running the OMP, e.g. TWR rx7\'s.

Have to agree with metalhead at the moment, for street car, OMP seems to offer more advantages.

[mullins]

Here\'s something else to throw in the pot:

Some of the drag cars in Oz run no oil injection at all.

[Mike]

Nice thread guys - shame I didn\'t stumble across it before.

My 2p, (4c - given today exchage rate!) worth is...

Not wanting to repeat any of the above, and agreeing with a lot of what has been said, for me I now feel I have the best setup - on a car that doesn\'t get used everyday and was built for good mid-range power and drivability not getting thrashed round a circuit - I have the omp with remote 2-stroke supply and semi-synth in the sump.

I must admit however to using (very roughly measured) premix during the break in period.

I think its the usual \'horses for courses\' - for a standard car, keep things standard, if its tuned and you have the desire to switch to 2-stroke use the OMP and a 2-stroke supply. If its a fire-breathing race car (or you just abuse it) then run premix. All have their advantages and pitfalls.

Mike.

[BlitzBoy]

Probably should re-word the bit I wrote about combustion occuring on overrun when the throttle is closed as its not really relevent and may not even be the case on injected cars. The point of the fact is the rotors are still spinning on overrun, therefore wear is occurring and as metalhead pointed out, only a very small amount of fuel will be entering the rotor chambers on a carbed car and even less/none on a fuel injected car so surely then an OMP system offers better lubrication in this scenario.

not strictly correct

On the Apexi ECU when on the overun, it still uses part of map therefore petrol is still being injected in small amounts, Ive seen it on the ghost trace on the datalogit. Also when using synth two stroke premix it leaves a small coating on housings and seals, so if there was no oil in the mix on the overun the seals are still protected for that short peroid of time on decel, as the 2 stroke residue would take time to fully burn up. Mr 88GTR can explain it better then me.
Ive seen certain drag cars use no Premix or OMP on mapping sessions

[BlitzBoy]

But I think we are all agreed that 2 stroke oil is better then dirty sump oil to lub up the seals

[oldone]

Nice thread guys - shame I didn\'t stumble across it before.

My 2p, (4c - given today exchage rate!) worth is...

Not wanting to repeat any of the above, and agreeing with a lot of what has been said, for me I now feel I have the best setup - on a car that doesn\'t get used everyday and was built for good mid-range power and drivability not getting thrashed round a circuit - I have the omp with remote 2-stroke supply and semi-synth in the sump.

I must admit however to using (very roughly measured) premix during the break in period.

I think its the usual \'horses for courses\' - for a standard car, keep things standard, if its tuned and you have the desire to switch to 2-stroke use the OMP and a 2-stroke supply. If its a fire-breathing race car (or you just abuse it) then run premix. All have their advantages and pitfalls.

Mike.

Bog standard motor..I would not bother with premix,....:chat  however the minute you build a motor to \'give it death\' then you have to take all precautions to protect it and make it perform properly.
Running a full blown race motor down the strip,....\'it might be beneficial\' to run withut ANY oil in the fuel.You can extrude every ounce of power from the fuel....albeit for a very short time,cos the motor will be rebuilt after a few hours of running anyway.Oil in the fuel may lead to \'detonation\' as it does not burn \'equal\' to the fuel.Cant give you tech specs only experience from running with and without.........:cool

[metalhead]

Just a note on the references to drag cars - just remember that for most drag cars engine longevity is not a major issue, oil in the combustion chamber lowers the effective octane rating of the fuel, the cars are only designed to run flat out for a few seconds at a time, rebuilds are expected relatively regularly and power is the ultimate aim above all else.  It makes sense not to have oil injection with these things considered.  Doesn\'t mean it\'s a good idea not to run it if you want a good life out of your street or circuit engine though.

[oldone]

Just a note on the references to drag cars - just remember that for most drag cars engine longevity is not a major issue, oil in the combustion chamber lowers the effective octane rating of the fuel, the cars are only designed to run flat out for a few seconds at a time, rebuilds are expected relatively regularly and power is the ultimate aim above all else.  It makes sense not to have oil injection with these things considered.  Doesn\'t mean it\'s a good idea not to run it if you want a good life out of your street or circuit engine though.

Are we twins ...............:evillaugh :cool

[metalhead]

Running a full blown race motor down the strip,....\'it might be beneficial\' to run withut ANY oil in the fuel.You can extrude every ounce of power from the fuel....albeit for a very short time,cos the motor will be rebuilt after a few hours of running anyway.Oil in the fuel may lead to \'detonation\' as it does not burn \'equal\' to the fuel.Cant give you tech specs only experience from running with and without.........:cool

Haha, beat me to it.

[BlitzBoy]

some Synth 2 stroke will not lower Octane levels, some actually increase AFRs John 88GTR has found some top notch stuff

[Dominic]

Guess the issue now is when does pre-mix become preferable to running the OMP. From the various posts in this thread this would appear not to be a specific rpm/engine type/fuelling type/or bhp but a rather hazy \'area\' which seems to be dependent on a a combination of these factors and others. I will do my best to summarise the info gathered from the folks who have contributed to this discussion and put down a few more things that I\'ve just thought of. Please add, amend, or make comment if I have misinterpreted:

Choice of Pre-mix - OMP - or both, dependent on:

1: The kind of driving/thrashing that the motor is going to have to put up with. A thrash motor/flame throwing race car prob better off on pre-mix whereas a stock or fast road car better off on OMP for reasons such as reduced oil consumption, less smell (not that that\'s a bad thing :Giggle ), less hassle with measuring cans.

2: Not really discussed in depth, but a higher revving motor may also be better suited to pre-mix due to the massive heat being produced in the engine and especially, the rotor tips. Reading on the other pre-mix thread http://www.mazdarotaryclub.com/forums/showthread.php?t=33006 BlitzBoy and Grizzly mentioned that tip warping can take place on high power OMP oiled rotors due to the temp difference between the injected oil and the tips (I assume they are referring to motors where the oil is injected directly through the housings rather than through the carb/injectors with the fuel and air). Presumably this applies to both turbo cars (on high boost) and high power N/A cars (high rpms). Pre-mix provides a more homogenous charge air/fuel/oil mix therefore elimating cool spots in the moving chambers and rotor tips (unless OMP is delivering oil to carb/injectors only).

3. Ultimate performance - Ultra high power cars ditching the oiling system in the quest for BIG hp but forking out to rebuild the block every week.

4. Less importantly but maybe still relevant - Whether the engine is Carb or EFI, and if EFI the specific map for the engine could dictate whether pre-mix or OMP is a better option. With a carb engine, the extent of porting could also be a factor, for example a big bridge port will reduce the vacuum in the carb considerably at low rpms and therefore less oil will be drawn into the engine when compared to a stock port motor at low revs.

5. Amount of usage - If a car is running pre-mix and is used very infrequently, oil separation may occur in the tank. This could cause insufficient lubrication to the engine on start up/first few minutes of driving due to the pre-mix oil sitting at the top of the tank.

6. This space reserved for oilman if he\'s reading this  I\'m sure he\'d have some comments....

Would be interesting to know how many 2nd and 3rd gen rx7 owners are out there running in excess of 400-500hp with the stock OMP and no pre-mix.

Regardless of the above, if running the OMP, the use of a standalone oil tank holding good clean 2 stroke oil from which the OMP draws from has got to be an improvement over the current system of drawing hot, dirty sump oil.

[BlitzBoy]

5. Amount of usage - If a car is running pre-mix and is used very infrequently, oil separation may occur in the tank. This could cause insufficient lubrication to the engine on start up/first few minutes of driving due to the pre-mix oil sitting at the top of the tank.

Synth two stroke mixes quite well with petrol from speaking to various people is does not seperate, so the seperation is bit of a myth.

[yoeddynz]

wow! longest thread I\'ve ever started...
I\'ve read all this now with two pints in me (discovered free broadband at my local pub but only 200m away from my garage) - I\'m going to go with premix for the following reasons....

1. I like the idea that once up and running my chevette can be taken on a long trip and so long as I premix I know i\'ll be covered on that front. I would hate to be driving along in the middle of france etc and wondering if the OMP is still working fine(sods law dictates..).    I rather just be worried about how much fuel I\'m using...

2. My car will be NA and with that I\'m going for the clean tidy engine bay look and the OMP with its pipes seems like just extra clutter.

3. I like the idea of using good quality synthetic oil for the sump and burning 2 stroke oil for premix.

4. The Idea of having a seperate bottle of oil which you have to check along with the associated extra gubbins sounds like just as much, if not more hassle then just premixing?

i\'ll just have to put a note on the fuel cap for others....