BOVs- do we need one ?
The compressor wheel has a sort of grip on the air molecules. as the air enters the front of the wheel, and rides along the wheel towards the outer tips, it gains momentum. Air molecules have a mass and air molecules can be sped up just like baseballs. The air compressor sort of "throws them" from the tips of it blade.
surge is more or less the point where the air no longer behaves the way I just described. Instead of being "slung" from the tips of the blade- the air molecules are allowed to slide backwards, moving towards the center of the wheel, and even out from the center back to the air filter. It is a kind of comparison of forces, we have the force that the wheel is applying to the air molecules as it spins, directing them outwards, which is based on RPM of the wheel and the weight of the air molecules I would surmise (thus compressor maps often include both somehow, or sometimes just volume/time leaving out mass although [mass/unit area] undoubtedly plays a role it may be negligible). And there is the force applied by the pressure on both sides of the wheel (which is also included on the map). The pressure on the center of the wheel is assumed to be atmospheric pressure or some baseline from which the map originates at its lowest region, which is why the side reads in pressure ratio as opposed to actual boost pressure. In other words, if atmospheric press was 5psi, then a pressure ratio of 2:1 would be 10psi and that is where you would read from on the left side at 5psi of boost (5psi of boost + 5psi of atm press = 10psi total) as you said, all engines are turbocharged.
By comparing pressure ratio and compressor rpm you can more or less 'read' the map, and determine which way the air will flow. If you are on the left side of the surge line, air molecules on the outlet of the compressor wheel will force their way back towards the inlet of the wheel, thus you are in a "surge" condition. Couple of things to note here, I think, one is the overall shape of most compressor maps sort of trends to the right as you move up. so if the given compressor spool too fast you might wind up on the left side of the surge line as boost pressure increases beyond what the engine will flow. this could happen if the turbine is tiny and the compressor large and the engine is tiny and at a low RPM (low flow rate). another thing to note is that there is no surge on the absolute right side of the map, the compressor only "falls off" and is either unable to maintain the required pressure ratio because of some maximum wheel rpm or other variable that has reached a limit, or in other cases it maintains the pressure ratio but the air is overheated because of the excessive wheel rpm. I do not manufacture compressor wheels so i am not sure about the exact science, but I do realize that with some higher wheel rpm there must be an increased friction or similar relationship regarding the wheels ability to "cut" or "hold" air molecules as it properly should.
surge is more or less the point where the air no longer behaves the way I just described. Instead of being "slung" from the tips of the blade- the air molecules are allowed to slide backwards, moving towards the center of the wheel, and even out from the center back to the air filter. It is a kind of comparison of forces, we have the force that the wheel is applying to the air molecules as it spins, directing them outwards, which is based on RPM of the wheel and the weight of the air molecules I would surmise (thus compressor maps often include both somehow, or sometimes just volume/time leaving out mass although [mass/unit area] undoubtedly plays a role it may be negligible). And there is the force applied by the pressure on both sides of the wheel (which is also included on the map). The pressure on the center of the wheel is assumed to be atmospheric pressure or some baseline from which the map originates at its lowest region, which is why the side reads in pressure ratio as opposed to actual boost pressure. In other words, if atmospheric press was 5psi, then a pressure ratio of 2:1 would be 10psi and that is where you would read from on the left side at 5psi of boost (5psi of boost + 5psi of atm press = 10psi total) as you said, all engines are turbocharged.
By comparing pressure ratio and compressor rpm you can more or less 'read' the map, and determine which way the air will flow. If you are on the left side of the surge line, air molecules on the outlet of the compressor wheel will force their way back towards the inlet of the wheel, thus you are in a "surge" condition. Couple of things to note here, I think, one is the overall shape of most compressor maps sort of trends to the right as you move up. so if the given compressor spool too fast you might wind up on the left side of the surge line as boost pressure increases beyond what the engine will flow. this could happen if the turbine is tiny and the compressor large and the engine is tiny and at a low RPM (low flow rate). another thing to note is that there is no surge on the absolute right side of the map, the compressor only "falls off" and is either unable to maintain the required pressure ratio because of some maximum wheel rpm or other variable that has reached a limit, or in other cases it maintains the pressure ratio but the air is overheated because of the excessive wheel rpm. I do not manufacture compressor wheels so i am not sure about the exact science, but I do realize that with some higher wheel rpm there must be an increased friction or similar relationship regarding the wheels ability to "cut" or "hold" air molecules as it properly should.
TECH Junkie
Joined: Jul 2015
Posts: 3,012
Likes: 48
The compressor wheel has a sort of grip on the air molecules. as the air enters the front of the wheel, and rides along the wheel towards the outer tips, it gains momentum. Air molecules have a mass and air molecules can be sped up just like baseballs. The air compressor sort of "throws them" from the tips of it blade.
surge is more or less the point where the air no longer behaves the way I just described. Instead of being "slung" from the tips of the blade- the air molecules are allowed to slide backwards, moving towards the center of the wheel, and even out from the center back to the air filter. It is a kind of comparison of forces, we have the force that the wheel is applying to the air molecules as it spins, directing them outwards, which is based on RPM of the wheel and the weight of the air molecules I would surmise (thus compressor maps often include both somehow, or sometimes just volume/time leaving out mass although [mass/unit area] undoubtedly plays a role it may be negligible). And there is the force applied by the pressure on both sides of the wheel (which is also included on the map). The pressure on the center of the wheel is assumed to be atmospheric pressure or some baseline from which the map originates at its lowest region, which is why the side reads in pressure ratio as opposed to actual boost pressure. In other words, if atmospheric press was 5psi, then a pressure ratio of 2:1 would be 10psi and that is where you would read from on the left side at 5psi of boost (5psi of boost + 5psi of atm press = 10psi total) as you said, all engines are turbocharged.
By comparing pressure ratio and compressor rpm you can more or less 'read' the map, and determine which way the air will flow. If you are on the left side of the surge line, air molecules on the outlet of the compressor wheel will force their way back towards the inlet of the wheel, thus you are in a "surge" condition. Couple of things to note here, I think, one is the overall shape of most compressor maps sort of trends to the right as you move up. so if the given compressor spool too fast you might wind up on the left side of the surge line as boost pressure increases beyond what the engine will flow. this could happen if the turbine is tiny and the compressor large and the engine is tiny and at a low RPM (low flow rate). another thing to note is that there is no surge on the absolute right side of the map, the compressor only "falls off" and is either unable to maintain the required pressure ratio because of some maximum wheel rpm or other variable that has reached a limit, or in other cases it maintains the pressure ratio but the air is overheated because of the excessive wheel rpm. I do not manufacture compressor wheels so i am not sure about the exact science, but I do realize that with some higher wheel rpm there must be an increased friction or similar relationship regarding the wheels ability to "cut" or "hold" air molecules as it properly should.
surge is more or less the point where the air no longer behaves the way I just described. Instead of being "slung" from the tips of the blade- the air molecules are allowed to slide backwards, moving towards the center of the wheel, and even out from the center back to the air filter. It is a kind of comparison of forces, we have the force that the wheel is applying to the air molecules as it spins, directing them outwards, which is based on RPM of the wheel and the weight of the air molecules I would surmise (thus compressor maps often include both somehow, or sometimes just volume/time leaving out mass although [mass/unit area] undoubtedly plays a role it may be negligible). And there is the force applied by the pressure on both sides of the wheel (which is also included on the map). The pressure on the center of the wheel is assumed to be atmospheric pressure or some baseline from which the map originates at its lowest region, which is why the side reads in pressure ratio as opposed to actual boost pressure. In other words, if atmospheric press was 5psi, then a pressure ratio of 2:1 would be 10psi and that is where you would read from on the left side at 5psi of boost (5psi of boost + 5psi of atm press = 10psi total) as you said, all engines are turbocharged.
By comparing pressure ratio and compressor rpm you can more or less 'read' the map, and determine which way the air will flow. If you are on the left side of the surge line, air molecules on the outlet of the compressor wheel will force their way back towards the inlet of the wheel, thus you are in a "surge" condition. Couple of things to note here, I think, one is the overall shape of most compressor maps sort of trends to the right as you move up. so if the given compressor spool too fast you might wind up on the left side of the surge line as boost pressure increases beyond what the engine will flow. this could happen if the turbine is tiny and the compressor large and the engine is tiny and at a low RPM (low flow rate). another thing to note is that there is no surge on the absolute right side of the map, the compressor only "falls off" and is either unable to maintain the required pressure ratio because of some maximum wheel rpm or other variable that has reached a limit, or in other cases it maintains the pressure ratio but the air is overheated because of the excessive wheel rpm. I do not manufacture compressor wheels so i am not sure about the exact science, but I do realize that with some higher wheel rpm there must be an increased friction or similar relationship regarding the wheels ability to "cut" or "hold" air molecules as it properly should.
After reading this, it made me think of something. Devon miles and Wilton Knight have now been dead for many years, and they've taken a valuable piece of information to the grave with them....the makeup of K.I.T.T.s molecular bonded shell. Can you please give us a complete comprehensive analysis of all components involved?
TECH Junkie
Joined: Jul 2015
Posts: 3,012
Likes: 48
get me a little bit of it, I have access to a High performance liquid chromatography and mass spec, an Nuclear magnetic resonance and of course light base spectroscopy methods, I am pretty sure we can figure it out. Anything except pollen, apparently. like my new sig? I never owned a talon, hope this clears things up.
Ok, I have another thread started here , "boost in first gear" and the answers have been very helpful, but since this can be a whole other topic and the other title doesnt get to this threads point, here goes.
I found that my HKS SQ4 BOV was leaking during a homemade leak down check/procedure . I have installed a "test" pipe in place of the pipe that holds the BOV and plugged the vac line . So...how bad is it on my turbo to just run without a BOV ? My turbo has the anti-surge compressor cover if that makes a difference.
I found that my HKS SQ4 BOV was leaking during a homemade leak down check/procedure . I have installed a "test" pipe in place of the pipe that holds the BOV and plugged the vac line . So...how bad is it on my turbo to just run without a BOV ? My turbo has the anti-surge compressor cover if that makes a difference.
This is 18-20psi with a BOV that worked - lol.
