Fabian
Well-Known Member
Now here is a man who knows what he is talking about - wise advise and carries a good knowledge base of 2-stroke engines and his data from dyno testing backs up my own experiences; consistant with my posts on the subject in previous threads.
Quote Spoom: Our tests were performed in the rpm range of 2500 to 9000 rpm... We started at 10:1, and went to 100:1. Our results showed that a two-stroke engine makes its best power at 18:1 ... The loss from 18:1 to 50:1 was nearly 9 percent... The loss from 18:1 to 100:1 was nearly 18 percent. The reason for the difference in output is simple. More oil provides a better seal between the ring and the cylinder wall.
With the high oil concentrations that I use, I tend to get far more life from my cranks and rings than most of my friends that run leaner oil ratios. The high oil content also produces better ring sealing, so more of the combustion pressure is retained. One small point. No one ever broke an engine by using too much oil.
My reply in kind: people who are using 2-stroke air cooled engines must understand that the piston to cylinder wall clearances are larger than water cooled engines to account for the extra expansion of metals under different ambient temperatures and running conditions.
This has in part the effect of reducing the stability of bore concentricity in relation to the piston rings, as a result of thermal variation in the cylinder barrel.
In a perfect world with an engine made to blueprint tollerances, piston rings would have a perfect surface to seal against.
If these factors were to be true, and lubrication were not required, the fuel (be it gasoline, petrol, whatever you may call it) would provide a fluid film to create a perfect seal against the cylinder bore.
The reality is actually very different - these Chinese engines are made with low quality metals and quality control that leaves much to be desired.
Bore distortion is a real problem under operating conditions and the piston rings have a seriously hard time trying to create a leak free compression stroke.
There is a solution though as explained by "spoom": The loss from 18:1 to 50:1 was nearly 9 percent... The loss from 18:1 to 100:1 was nearly 18 percent. The reason for the difference in output is simple. More oil provides a better seal between the ring and the cylinder wall.
Not only does the extra oil provide a far better hydrodynamic seal but it also has the ability to absorb heat and help minimise excessive bore distortion by drawing excess heat away from the hot spots along the exhaust side of the cylinder.
I think that comment should end all argument, unless using castor oil, but thats a whole new scenario and worth of a topic of discussion on it's own.
With high quality Japanese water cooled 2-stroke engines, it's a different scenario again but it all comes down to the quality of metalurgy and water cooling to keep bore distortion to absolute minimums, providing good ring seal with minimal oil quantity.
Having said that, even Japanese engines will make more power with more oil in the fuel, even though the extra oil is reducing the octane rating and ever so slightly leaning out the mixture.
It's all about the hydrodynamic aspects of piston rings working against an inconsistant bore surface.
Fabian
Quote Spoom: Our tests were performed in the rpm range of 2500 to 9000 rpm... We started at 10:1, and went to 100:1. Our results showed that a two-stroke engine makes its best power at 18:1 ... The loss from 18:1 to 50:1 was nearly 9 percent... The loss from 18:1 to 100:1 was nearly 18 percent. The reason for the difference in output is simple. More oil provides a better seal between the ring and the cylinder wall.
With the high oil concentrations that I use, I tend to get far more life from my cranks and rings than most of my friends that run leaner oil ratios. The high oil content also produces better ring sealing, so more of the combustion pressure is retained. One small point. No one ever broke an engine by using too much oil.
My reply in kind: people who are using 2-stroke air cooled engines must understand that the piston to cylinder wall clearances are larger than water cooled engines to account for the extra expansion of metals under different ambient temperatures and running conditions.
This has in part the effect of reducing the stability of bore concentricity in relation to the piston rings, as a result of thermal variation in the cylinder barrel.
In a perfect world with an engine made to blueprint tollerances, piston rings would have a perfect surface to seal against.
If these factors were to be true, and lubrication were not required, the fuel (be it gasoline, petrol, whatever you may call it) would provide a fluid film to create a perfect seal against the cylinder bore.
The reality is actually very different - these Chinese engines are made with low quality metals and quality control that leaves much to be desired.
Bore distortion is a real problem under operating conditions and the piston rings have a seriously hard time trying to create a leak free compression stroke.
There is a solution though as explained by "spoom": The loss from 18:1 to 50:1 was nearly 9 percent... The loss from 18:1 to 100:1 was nearly 18 percent. The reason for the difference in output is simple. More oil provides a better seal between the ring and the cylinder wall.
Not only does the extra oil provide a far better hydrodynamic seal but it also has the ability to absorb heat and help minimise excessive bore distortion by drawing excess heat away from the hot spots along the exhaust side of the cylinder.
I think that comment should end all argument, unless using castor oil, but thats a whole new scenario and worth of a topic of discussion on it's own.
With high quality Japanese water cooled 2-stroke engines, it's a different scenario again but it all comes down to the quality of metalurgy and water cooling to keep bore distortion to absolute minimums, providing good ring seal with minimal oil quantity.
Having said that, even Japanese engines will make more power with more oil in the fuel, even though the extra oil is reducing the octane rating and ever so slightly leaning out the mixture.
It's all about the hydrodynamic aspects of piston rings working against an inconsistant bore surface.
Fabian