engineers plz help
- Thread starter movinfast
- Start date
I'm no engineer, but from what I quickly read thats basically pressure inside the cylinder, most (wrongly) refer to it as the compression ratio. In which case, standard physics tells me when the compression of gas and air reaches a point that comes close to overcoming the explosive forces of the gasoline and friction of the motor, which, would be alot. You'll face detonation and breaking heads, crank cases and gaskets long before your compression becomes so much it loses power, so in practical terms, there's no limit to the amount of compression you can have.
However... I could be wayyyyyy off base and mistaken what BMEP is, in which case I'm sure there will be someone on this forum who can clarify
However... I could be wayyyyyy off base and mistaken what BMEP is, in which case I'm sure there will be someone on this forum who can clarify
I am studying automotives... Gonna go ahead and hope that I have valid knowledge to chime in for this.
First, read this: http://www.epi-eng.com/piston_engine_technology/bmep_performance_yardstick.htm
BMEP is not correlated to actual chamber psi, and, it is simply a rating. Kind of like the term "horsepower"; it is not directly usable in the real world, but it is a rating.
Anyway, seeing as BMEP is nothing more than a rating and is not actually related to the real cylinder pressures, there is NO point where a higher BMEP would equal less power. It will always mean more.
If, on the other hand, you mixed up BMEP and whatever term you wanted to use for actual cylinder pressure; again, there is no point.
Pressure in an engine is measured by the volume of air in the chamber at BDC, and how much pressure is generated at TDC. This works with two variables=
How much air is in the chamber, and, how much it is compressed.
How much air is in the chamber is controlled by many things. They are largely modified by superchargers and turbochargers just as you said, but, simple airflow changes such as new intake manifolds, cams, exhaust manifolds, carburetors, etc. also affect a term called "volumetric efficiency", or, for your uses, how much air is in the cylinder. So basically, ANY MOD touching ANY of the gasses going in or out of the engine will affect VE (volumetric efficiency.) Yes, this includes the piston itself and the cylinder walls.
How much it is compressed is simply measured in static compression ratio.
Either way, more psi is always more power; while it may also equate to more heat, gas usage and other bad things, more pressure means more force; and more force means more force pushing the piston down and therefore resulting on the other end of the crankshaft, and, eventually, at the ground.
First, read this: http://www.epi-eng.com/piston_engine_technology/bmep_performance_yardstick.htm
BMEP is not correlated to actual chamber psi, and, it is simply a rating. Kind of like the term "horsepower"; it is not directly usable in the real world, but it is a rating.
Anyway, seeing as BMEP is nothing more than a rating and is not actually related to the real cylinder pressures, there is NO point where a higher BMEP would equal less power. It will always mean more.
If, on the other hand, you mixed up BMEP and whatever term you wanted to use for actual cylinder pressure; again, there is no point.
Pressure in an engine is measured by the volume of air in the chamber at BDC, and how much pressure is generated at TDC. This works with two variables=
How much air is in the chamber, and, how much it is compressed.
How much air is in the chamber is controlled by many things. They are largely modified by superchargers and turbochargers just as you said, but, simple airflow changes such as new intake manifolds, cams, exhaust manifolds, carburetors, etc. also affect a term called "volumetric efficiency", or, for your uses, how much air is in the cylinder. So basically, ANY MOD touching ANY of the gasses going in or out of the engine will affect VE (volumetric efficiency.) Yes, this includes the piston itself and the cylinder walls.
How much it is compressed is simply measured in static compression ratio.
Either way, more psi is always more power; while it may also equate to more heat, gas usage and other bad things, more pressure means more force; and more force means more force pushing the piston down and therefore resulting on the other end of the crankshaft, and, eventually, at the ground.
One potential issue with this is you may start to have engine knocking, leading to high vibration. This occurs when pressure in the cylinder is too high. Safe compression ratio for low-grade gas is limited to about 10:1, i.e. ten times atmospheric. Below that, I don't see why you should have any problem, other than that some of the engine components may not be built to take those kinds of pressures. But that wasn't your question; it was regarding bmep-
More bmep will always mean more power, but make sure that the extra pressure (break mean effective pressure) won't break any of your engine parts.
More bmep will always mean more power, but make sure that the extra pressure (break mean effective pressure) won't break any of your engine parts.
