Gas/Oil Premix Thread
07-22-2008, 02:20 AM
#1353
Super Moderator
Fine if you are "racing" or 'track' your RX-8?..NO..
I suggest halve that amount for 'normal' use...
I suggest halve that amount for 'normal' use...
07-26-2008, 07:44 PM
#1354
Another thought I was having about premix .
In the stock setup oil seeps onto the housing rather than being injected into the chamber to mix with the fuel .
Premix oil is designed to mix with fuel and privide lubrication to the combustion chamber via the fuel .
This begs the question :
Does premix oil (using sohn adaptor) work as well as engine oil when applied the way it is ?
07-27-2008, 05:23 AM
#1357
Registered
That is not how the oil is distributed in the chamber from premix.
The atomized oil and fuel is mostly in the air, with just a little hitting the combustion chamber (and other) surfaces until the explosion of combustion - at that time all the oil particles, because they are heavier and do not burn as fast a fuel, are literally thrown to all the edges and cover everything until they get hot enough to eventually burn (which takes much longer, relatively speaking, than the fuel)- think of it as a splatter effect like you put a firecracker in the middle of a water balloon.
Thus, premixing will always put usable oil in the combustion chamber, independent of if it is direct injection or port injection.
The atomized oil and fuel is mostly in the air, with just a little hitting the combustion chamber (and other) surfaces until the explosion of combustion - at that time all the oil particles, because they are heavier and do not burn as fast a fuel, are literally thrown to all the edges and cover everything until they get hot enough to eventually burn (which takes much longer, relatively speaking, than the fuel)- think of it as a splatter effect like you put a firecracker in the middle of a water balloon.
Thus, premixing will always put usable oil in the combustion chamber, independent of if it is direct injection or port injection.
07-27-2008, 08:53 AM
#1358
Registered
A little math (please pardon the mix of units):
Assume 1 liter of oil is consumed per 3000 miles of normal highway driving, and that at 60 mph the engine speed is 3000 rpm. Then the total revolutions for 3000 miles = (3000/60)(60)(3000) = 9,000,000.
Under these conditions only the small pistons in the MOP are active, so an oil injection is provided every 22 revolutions of the eccentric (output) shaft. Therefore there are 9000000/22 = 409,091 injections. The volume of each injection will then be 1000/409,091 = 0.00244 cc = 2.44 cubic mm.
Each of these MOP injections actually feeds two combustion chamber injectors, so each of the latter will see half of the above, i.e. 1.22 cubic mm.
Now the period over which this volume is delivered to any particular combustion chamber injector is the time it takes for 11 shaft revolutions (no delivery to that injector during the next 11 revolutions), which in this case equals (60/3000)(11) = 0.22 seconds. Therefore the average flow rate during injection is 1.22/0.22 = 5.56 cubic mm per second.
I do not know what the diameter of the oil injection holes are, but say they are 1/16 inch, or about 1.5 mm. Then the cross-sectional area of each hole would be (pi/4)(1.5)(1.5) = 1.77 square mm. The average flow velocity would then be 5.56/1.77 = 3.14 mm per second, i.e. it would take about 8 seconds for the 'stream' to travel about 1 inch.
By 'quite a spurt', one might reasonably expect a minimum flow velocity of say, 1 m/s (1000 mm/s). Therefore, given that the above calculations and assumptions are close to being correct, perhaps the nature of the injection is better viewed as 'dribbling'.
Assume 1 liter of oil is consumed per 3000 miles of normal highway driving, and that at 60 mph the engine speed is 3000 rpm. Then the total revolutions for 3000 miles = (3000/60)(60)(3000) = 9,000,000.
Under these conditions only the small pistons in the MOP are active, so an oil injection is provided every 22 revolutions of the eccentric (output) shaft. Therefore there are 9000000/22 = 409,091 injections. The volume of each injection will then be 1000/409,091 = 0.00244 cc = 2.44 cubic mm.
Each of these MOP injections actually feeds two combustion chamber injectors, so each of the latter will see half of the above, i.e. 1.22 cubic mm.
Now the period over which this volume is delivered to any particular combustion chamber injector is the time it takes for 11 shaft revolutions (no delivery to that injector during the next 11 revolutions), which in this case equals (60/3000)(11) = 0.22 seconds. Therefore the average flow rate during injection is 1.22/0.22 = 5.56 cubic mm per second.
I do not know what the diameter of the oil injection holes are, but say they are 1/16 inch, or about 1.5 mm. Then the cross-sectional area of each hole would be (pi/4)(1.5)(1.5) = 1.77 square mm. The average flow velocity would then be 5.56/1.77 = 3.14 mm per second, i.e. it would take about 8 seconds for the 'stream' to travel about 1 inch.
By 'quite a spurt', one might reasonably expect a minimum flow velocity of say, 1 m/s (1000 mm/s). Therefore, given that the above calculations and assumptions are close to being correct, perhaps the nature of the injection is better viewed as 'dribbling'.
07-27-2008, 07:33 PM
#1359
Got Another Rotary
2-cycle oils do not have to worry about lasting, so they have no use for antioxidants and many other ingredients that a 4-cycle oil needs (around 30% of a 4-cycle oils total package) to have a long service life because the 2-cycle's service life is a few milli-seconds - so all the ingredients can focus on it's mission of a clean burning lubrication of a very short duration.
MM - I saw your post that you started mixing 2 and 4 cycle 50/50 in your tank - rather than that, you would be better off increasing you OMP rates with pure 2-cycle if you have reservations (via your COBB). 4-cycle oils really do gums things up inside a combustion chamber pretty bad and since you went to the trouble of adding the Sohn, hate to see you not get the full benefit.
07-27-2008, 07:36 PM
#1360
Got Another Rotary
A little math (please pardon the mix of units):
Assume 1 liter of oil is consumed per 3000 miles of normal highway driving, and that at 60 mph the engine speed is 3000 rpm. Then the total revolutions for 3000 miles = (3000/60)(60)(3000) = 9,000,000.
Under these conditions only the small pistons in the MOP are active, so an oil injection is provided every 22 revolutions of the eccentric (output) shaft. Therefore there are 9000000/22 = 409,091 injections. The volume of each injection will then be 1000/409,091 = 0.00244 cc = 2.44 cubic mm.
Each of these MOP injections actually feeds two combustion chamber injectors, so each of the latter will see half of the above, i.e. 1.22 cubic mm.
Now the period over which this volume is delivered to any particular combustion chamber injector is the time it takes for 11 shaft revolutions (no delivery to that injector during the next 11 revolutions), which in this case equals (60/3000)(11) = 0.22 seconds. Therefore the average flow rate during injection is 1.22/0.22 = 5.56 cubic mm per second.
I do not know what the diameter of the oil injection holes are, but say they are 1/16 inch, or about 1.5 mm. Then the cross-sectional area of each hole would be (pi/4)(1.5)(1.5) = 1.77 square mm. The average flow velocity would then be 5.56/1.77 = 3.14 mm per second, i.e. it would take about 8 seconds for the 'stream' to travel about 1 inch.
By 'quite a spurt', one might reasonably expect a minimum flow velocity of say, 1 m/s (1000 mm/s). Therefore, given that the above calculations and assumptions are close to being correct, perhaps the nature of the injection is better viewed as 'dribbling'.
Assume 1 liter of oil is consumed per 3000 miles of normal highway driving, and that at 60 mph the engine speed is 3000 rpm. Then the total revolutions for 3000 miles = (3000/60)(60)(3000) = 9,000,000.
Under these conditions only the small pistons in the MOP are active, so an oil injection is provided every 22 revolutions of the eccentric (output) shaft. Therefore there are 9000000/22 = 409,091 injections. The volume of each injection will then be 1000/409,091 = 0.00244 cc = 2.44 cubic mm.
Each of these MOP injections actually feeds two combustion chamber injectors, so each of the latter will see half of the above, i.e. 1.22 cubic mm.
Now the period over which this volume is delivered to any particular combustion chamber injector is the time it takes for 11 shaft revolutions (no delivery to that injector during the next 11 revolutions), which in this case equals (60/3000)(11) = 0.22 seconds. Therefore the average flow rate during injection is 1.22/0.22 = 5.56 cubic mm per second.
I do not know what the diameter of the oil injection holes are, but say they are 1/16 inch, or about 1.5 mm. Then the cross-sectional area of each hole would be (pi/4)(1.5)(1.5) = 1.77 square mm. The average flow velocity would then be 5.56/1.77 = 3.14 mm per second, i.e. it would take about 8 seconds for the 'stream' to travel about 1 inch.
By 'quite a spurt', one might reasonably expect a minimum flow velocity of say, 1 m/s (1000 mm/s). Therefore, given that the above calculations and assumptions are close to being correct, perhaps the nature of the injection is better viewed as 'dribbling'.
Wow - I didn't know it took that much math to prove a "dribble"!
What if was a full-fledged "Drool"?
07-27-2008, 07:53 PM
#1362
thanks again..
i will let you know. that mm oil schedule for the omp. is way high...
he has done that with the ap. not really sure of the scale, but i think the last flash is maybe a 8 on the omp. the mm flash he is using is a 13..
and i am pulling that out of the back of my readings.. he has way increased the omp schedule.. not sure if he has done it with all he has shipped, but his own. yes.
beers
07-27-2008, 07:54 PM
#1363
MM - I saw your post that you started mixing 2 and 4 cycle 50/50 in your tank - rather than that, you would be better off increasing you OMP rates with pure 2-cycle if you have reservations (via your COBB). 4-cycle oils really do gums things up inside a combustion chamber pretty bad and since you went to the trouble of adding the Sohn, hate to see you not get the full benefit.
Stock is 3 at idle. I do 11 - 13.
07-27-2008, 08:17 PM
#1365
Registered
07-28-2008, 06:56 AM
#1369
Got Another Rotary
Exactly, you could say that one of the issues with 4-cycle is that it does not burn fast enough (as 4-cycle is designed to not vaporize so you don't have oil loss in an engine sump with high temps) - thus some hangs around through multiple cycles and gums things up inside the engine and the rest is thrown into the cat and gums it up. Not good for either.
Last edited by Jax_RX8; 07-28-2008 at 07:02 AM.
07-28-2008, 07:00 AM
#1370
Got Another Rotary
What is you oil usage at that setting? Are you still premixing with that setting?
07-28-2008, 07:40 AM
#1371
Registered
07-28-2008, 07:51 AM
#1372
Registered
Dont get me wrong---I will never say stop pre mixing and the respect is mutual. I am just one little fella sharing what he has seen and based on that I need more evidence to concur that a very low ratio of pre mix does anything in reference to wear and longitivity. I understand the idle may be a little better and other subjective observances may occur but it remains to be seen that low ratio pre mix will make the engine last longer. No one to my knowledge has ever demonstrated this. I have seen two engines firsthand that premixed most of their lives with substantial wear on the housings. I know of a couple more that had to have new engines due to low compression issues. Maybe the MOP is not working well and other things may have happened also, I dont know.
I do know that on my own 1st engine that a ratio of 1/2 oz per gal my vacuum readings did go up. Anything less it did not. I pre mixed that engine for a long time. When i tore it down the wear surprised me.
Now i still pre mix on the street at 1/2 oz per gal(i do not have a cat) and i do run 1 oz per gal at the track and at that ratio you can smell the oil.
I just dont expect the pre mixing to help the engine live any longer,
rotor on
olddragger
I do know that on my own 1st engine that a ratio of 1/2 oz per gal my vacuum readings did go up. Anything less it did not. I pre mixed that engine for a long time. When i tore it down the wear surprised me.
Now i still pre mix on the street at 1/2 oz per gal(i do not have a cat) and i do run 1 oz per gal at the track and at that ratio you can smell the oil.
I just dont expect the pre mixing to help the engine live any longer,rotor on
olddragger
OD, you once said you opened up the weep holes in the rotor housings. Do you remember what the drill sizes were?
07-28-2008, 09:06 AM
#1373
Registered
You really can't talk about what the pump puts out unless you quote the step number. At step 0 the output is zero. The output at step 60 is more than 500 times that at step 1, and there is a significant step change in output beginning at around step 20.
It's difficult to do the test you talk about without using something like a Shon adapter, and a proper nozzle. The latter is especially important because of the square dependence of velocity on the diameter.
There is however, probably something to what you say because of the injection setup at the rotor housing. The picture shows the injection nozzles directed towards the sides, and a 'spurting', but directing the flow in this manner could only come about because of a very small hole in the nozzles.
OD - the question I asked about the housing holes is probably not as relevant now that it seems the nozzle design probably dominates flow characteristics, but their size would still be interesting to know
07-28-2008, 10:46 AM
#1374
i dont remember the size but i will pull the housing(i did this on old housings --not the engine i am running now) and see.
matter of fact i may hook up an omp with the nozzle in the housing(without the rotor in it) put the omp on a drill or something and see what happens. i have one housing where i enlarge the weep holes slightly and the other is oem.
may be interesting.
currently trying to figue out a way to use frame rail coolers for supplemental engine cooling, so i needed another experiment to keep me busy. stay tuned.
OD
matter of fact i may hook up an omp with the nozzle in the housing(without the rotor in it) put the omp on a drill or something and see what happens. i have one housing where i enlarge the weep holes slightly and the other is oem.
may be interesting.
currently trying to figue out a way to use frame rail coolers for supplemental engine cooling, so i needed another experiment to keep me busy. stay tuned.
OD
07-28-2008, 03:16 PM
#1375
Registered
Exactly, you could say that one of the issues with 4-cycle is that it does not burn fast enough (as 4-cycle is designed to not vaporize so you don't have oil loss in an engine sump with high temps) - thus some hangs around through multiple cycles and gums things up inside the engine and the rest is thrown into the cat and gums it up. Not good for either.
Last edited by robrecht; 07-28-2008 at 03:27 PM.