Do these pictures need captions? (32V Intake Manifold Study - HP)
04-21-2013, 04:31 PM
#47
Former Vendor
Thread Starter
Yes. I was forced to "set it" on a shelf for a long period of time....I quite simply "ran out of talent" and could not finish it, without help. Up to that point, I'd worked on it for about 5 weeks....2 weeks of which were just drawings and measurements. Just the "space problem" is a real issue. (Multiply 2.25" by 8 pipes....that's 18". Add in another 4" for a pipe to get into the throttle body. That's 22", really quick....if every pipe touches the other pipe, perfectly. Now go out to your car and measure 22", behind the cross brace. The problem gets really clear, really quickly.)
I now have a good fabricator/welder working for me. We pulled it back out and together we worked for another 3 weeks (to date) to get it to this point.
In a lighter moment, after a few long days of absolute "thrashing" trying to make a proper plenum, we actually had a great laugh. I joked that it would have been much easier if we could have gotten aluminum in bigger pieces than 2" x 2". (The lower plenum has been cut up and modified so many times, it is a true "patch work" of pieces.....the "butterfly", alone, has been moved six separate times...and that's just a "modification" of this version...not a whole new version.)
It is not a simple little thing. Like I said, hardest thing I've ever done.
It does make me wonder. How many engineers, fabricators, and people to test fit did it take to make the first manifold for the Cayenne....and how much did the very first one of those cost to make?
I now have a good fabricator/welder working for me. We pulled it back out and together we worked for another 3 weeks (to date) to get it to this point.
In a lighter moment, after a few long days of absolute "thrashing" trying to make a proper plenum, we actually had a great laugh. I joked that it would have been much easier if we could have gotten aluminum in bigger pieces than 2" x 2". (The lower plenum has been cut up and modified so many times, it is a true "patch work" of pieces.....the "butterfly", alone, has been moved six separate times...and that's just a "modification" of this version...not a whole new version.)
It is not a simple little thing. Like I said, hardest thing I've ever done.
It does make me wonder. How many engineers, fabricators, and people to test fit did it take to make the first manifold for the Cayenne....and how much did the very first one of those cost to make?
04-21-2013, 04:49 PM
#48
Addict
Lifetime Rennlist
Member
Lifetime Rennlist
Member
Great question!
An engine is an air pump. The more air you can push in and out, the more power it will make (assuming that you add/mix enough fuel to use that air).
My current limit is that I can't get any more air into my engines.....and even if I make changes to get more air....the fuel required just "runs" down the ports and makes puddles.
This manifold is all about getting more air into my engines.....and a couple more little details....like significantly better fuel mixing....and cooler air.
04-21-2013, 05:13 PM
#49
Former Vendor
Thread Starter
Yes, but because that volume of air is "drawn in", the volume that can be drawn in can vary quite a bit. Depending on how restrictive and how well a manifold works, the actual volume that is drawn in (volumetric efficiency) can vary from 60% to 120%. Your lawnmower probably works at about 60%. A very well developed natural aspirated engine can work at more than 100%, by using the pulses in the intake system. This is called "inertial supercharging". When an intake valve shuts. the air pulse that is moving down that runner hits the back of the intake valve, it bounces off that valve and goes backwards in the runner. The forces in the intake system/engine make that "pulse" reverse and then go back towards the valve, before it opens. If you can "time" that "arriving" pulse, to the exact moment that the valve opens, there will actually be air pressure just behind the valve and air will be forced past that valve, into the cylinder. Runner length is very important, for this to happen at the correct moment.
04-21-2013, 05:43 PM
#50
Nordschleife Master
This is called "inertial supercharging". When an intake valve shuts. the air pulse that is moving down that runner hits the back of the intake valve, it bounces off that valve and goes backwards in the runner. The forces in the intake system/engine make that "pulse" reverse and then go back towards the valve, before it opens. If you can "time" that "arriving" pulse, to the exact moment that the valve opens, there will actually be air pressure just behind the valve and air will be forced past that valve, into the cylinder. Runner length is very important, for this to happen at the correct moment.
One way to see why this must be the case is to consider the optimal intake valve closing time. If the engine is well tuned for the rpm at which it's operating, almost by definition the intake valve closes at the optimal time. What is the optimal time? Turns out that the optimal time is before the air has started moving backwards but after it no longer is moving forward -- that is, when the air is not moving in either direction at the valve. Any closing the valve earlier would reduce the cylinder filling, as would any closing of the valve later, hence it's the optimal timing. If the intake valve is closed at the optimal time when air is not moving at the valve, then valve closing can't cause any "inertia" pulse either. Thus, the common belief that air column hitting a closed valve causes the pulse is wrong, at least for well tuned engines.
What causes the pulse then? It's my understanding that the pressure wave is caused by the piston first decelerating before the BDC and then moving up in the cylinder. The piston moving up in the cylinder combined with the inertia of the air column moving down causes a pressure increase in the cylinder. The pressure increase spreads upstream thru the port and imposes a force on the air column, decelerating it. The air column stops when the pressure force overcomes the air column inertia, at which point the pressure in the intake port is quite high. The valve closes at that optimal point, but this doesn't cause a pulse. Rather, the high pressure that _is_ the pulse is already in the port and around the valve when the valve closes. The pressure wave travels up the runner (and in an isolated runner single plenum manifold will be reflected back as rarefaction wave towards the valve, etc.)
The 1D simulators appear consistent with this, as they show a strong pulse even when the intake valve is closed exactly at the optimal time when the local air speed at the valve is zero. The wave starts building as the piston approaches the BDC.
At least this is how I've understood it to work out.
04-21-2013, 05:59 PM
#51
Former Vendor
Thread Starter
In a well tuned engine at the rpm to which it is tuned, the intake valve closing does not cause a meaningful pulse in the intake port or runner.
One way to see why this must be the case is to consider the optimal intake valve closing time. If the engine is well tuned for the rpm at which it's operating, almost by definition the intake valve closes at the optimal time. What is the optimal time? Turns out that the optimal time is before the air has started moving backwards but after it no longer is moving forward -- that is, when the air is not moving in either direction at the valve. Any closing the valve earlier would reduce the cylinder filling, as would any closing of the valve later, hence it's the optimal timing. If the intake valve is closed at the optimal time when air is not moving at the valve, then valve closing can't cause any "inertia" pulse either. Thus, the common belief that air column hitting a closed valve causes the pulse is wrong, at least for well tuned engines.
What causes the pulse then? It's my understanding that the pressure wave is caused by the piston first decelerating before the BDC and then moving up in the cylinder. The piston moving up in the cylinder combined with the inertia of the air column moving down causes a pressure increase in the cylinder. The pressure increase spreads upstream thru the port and imposes a force on the air column, decelerating it. The air column stops when the pressure force overcomes the air column inertia, at which point the pressure in the intake port is quite high. The valve closes at that optimal point, but this doesn't cause a pulse. Rather, the high pressure that _is_ the pulse is already in the port and around the valve when the valve closes. The pressure wave travels up the runner (and in an isolated runner single plenum manifold will be reflected back as rarefaction wave towards the valve, etc.)
The 1D simulators appear consistent with this, as they show a strong pulse even when the intake valve is closed exactly at the optimal time when the local air speed at the valve is zero. The wave starts building as the piston approaches the BDC.
At least this is how I've understood it to work out.
One way to see why this must be the case is to consider the optimal intake valve closing time. If the engine is well tuned for the rpm at which it's operating, almost by definition the intake valve closes at the optimal time. What is the optimal time? Turns out that the optimal time is before the air has started moving backwards but after it no longer is moving forward -- that is, when the air is not moving in either direction at the valve. Any closing the valve earlier would reduce the cylinder filling, as would any closing of the valve later, hence it's the optimal timing. If the intake valve is closed at the optimal time when air is not moving at the valve, then valve closing can't cause any "inertia" pulse either. Thus, the common belief that air column hitting a closed valve causes the pulse is wrong, at least for well tuned engines.
What causes the pulse then? It's my understanding that the pressure wave is caused by the piston first decelerating before the BDC and then moving up in the cylinder. The piston moving up in the cylinder combined with the inertia of the air column moving down causes a pressure increase in the cylinder. The pressure increase spreads upstream thru the port and imposes a force on the air column, decelerating it. The air column stops when the pressure force overcomes the air column inertia, at which point the pressure in the intake port is quite high. The valve closes at that optimal point, but this doesn't cause a pulse. Rather, the high pressure that _is_ the pulse is already in the port and around the valve when the valve closes. The pressure wave travels up the runner (and in an isolated runner single plenum manifold will be reflected back as rarefaction wave towards the valve, etc.)
The 1D simulators appear consistent with this, as they show a strong pulse even when the intake valve is closed exactly at the optimal time when the local air speed at the valve is zero. The wave starts building as the piston approaches the BDC.
At least this is how I've understood it to work out.
However, the result is the same....inertial supercharging (cylinder filling over 100%)....if the pulse can be properly contained in the intake runner and not "escape" into the plenum. The length of the intake runner and the rpm where this happens is very important.
04-21-2013, 06:22 PM
#52
I think that this explanation from Wikipedia is a good one;
"The design and orientation of the intake manifold is a major factor in the volumetric efficiency of an engine. Abrupt contour changes provoke pressure drops, resulting in less air (and/or fuel) entering the combustion chamber; high-performance manifolds have smooth contours and gradual transitions between adjacent segments.
Modern intake manifolds usually employ runners, individual tubes extending to each intake port on the cylinder head which emanate from a central volume or "plenum" beneath the carburetor. The purpose of the runner is to take advantage of the Helmholtz resonance property of air. Air flows at considerable speed through the open valve. When the valve closes, the air that has not yet entered the valve still has a lot of momentum and compresses against the valve, creating a pocket of high pressure. This high-pressure air begins to equalize with lower-pressure air in the manifold. Due to the air's inertia, the equalization will tend to oscillate: At first the air in the runner will be at a lower pressure than the manifold. The air in the manifold then tries to equalize back into the runner, and the oscillation repeats. This process occurs at the speed of sound, and in most manifolds travels up and down the runner many times before the valve opens again.
The smaller the cross-sectional area of the runner, the higher the pressure changes on resonance for a given airflow. This aspect of Helmholz resonance reproduces one result of the Venturi effect. When the piston accelerates downwards, the pressure at the output of the intake runner is reduced. This low pressure pulse runs to the input end, where it is converted into an over-pressure pulse. This pulse travels back through the runner and rams air through the valve. The valve then closes.
To harness the full power of the Helmholtz resonance effect, the opening of the intake valve must be timed correctly, otherwise the pulse could have a negative effect. This poses a very difficult problem for engines, since valve timing is dynamic and based on engine speed, whereas the pulse timing is static and dependent on the length of the intake runner and the speed of sound. The traditional solution has been to tune the length of the intake runner for a specific engine speed where maximum performance is desired. However, modern technology has given rise to a number of solutions involving electronically controlled valve timing (for example Valvetronic), and dynamic intake geometry (see below).
As a result of "resonance tuning", some naturally aspirated intake systems operate at a volumetric efficiency above 100%: the air pressure in the combustion chamber before the compression stroke is greater than the atmospheric pressure. In combination with this intake manifold design feature, the exhaust manifold design, as well as the exhaust valve opening time can be so calibrated as to achieve greater evacuation of the cylinder. The exhaust manifolds achieve a vacuum in the cylinder just before the piston reaches top dead center.[citation needed] The opening inlet valve can then—at typical compression ratios—fill 10% of the cylinder before beginning downward travel.[citation needed] Instead of achieving higher pressure in the cylinder, the inlet valve can stay open after the piston reaches bottom dead center while the air still flows in.[citation needed][vague]
In some engines the intake runners are straight for minimal resistance. In most engines, however, the runners have curves...and some very convoluted to achieve desired runner length. These turns allow for a more compact manifold, with denser packaging of the whole engine, as a result. Also, these "snaked" runners are needed for some variable length/ split runner designs, and allow the size of the plenum to be reduced. In an engine with at least six cylinders the averaged intake flow is nearly constant and the plenum volume can be smaller. To avoid standing waves within the plenum it is made as compact as possible. The intake runners each use a smaller part of the plenum surface than the inlet, which supplies air to the plenum, for aerodynamic reasons. Each runner is placed to have nearly the same distance to the main inlet. Runners, whose cylinders fire close after each other, are not placed as neighbors.
"180-degree intake manifolds"....Originally designed for carburetor V8 engines, the two plane, split plenum intake manifold separates the intake pulses which the manifold experiences by 180 degrees in the firing order. This minimizes interference of one cylinder's pressure waves with those of another, giving better torque from smooth mid-range flow. Such manifolds may have been originally designed for either two- or four-barrel carburetors, but now are used with both throttle-body and multi-point fuel injection. An example of the latter is the Honda J engine which converts to a single plane manifold around 3500 rpm for greater peak flow and horsepower.
"Heat Riser"....now obsolete, earlier manifolds ...with 'wet runners' for carbureted engines...used exhaust gas diversion through the intake manifold to provide vaporizing heat. The amount of exhaust gas flow diversion was controlled by a heat riser valve in the exhaust manifold, and employed a bi-metallic spring which changed tension according to the heat in the manifold. Today's fuel-injected engines do not require such devices."
Then for a visual on the actual waves, they can be seen in this video, you can see the intake charge blowing back, the air would be traveling at a speed in the 0.55 to 0.60 Mach range.
The highest volumetric efficiency I have heard of is 145%
Good luck with the manifold testing Greg.
"The design and orientation of the intake manifold is a major factor in the volumetric efficiency of an engine. Abrupt contour changes provoke pressure drops, resulting in less air (and/or fuel) entering the combustion chamber; high-performance manifolds have smooth contours and gradual transitions between adjacent segments.
Modern intake manifolds usually employ runners, individual tubes extending to each intake port on the cylinder head which emanate from a central volume or "plenum" beneath the carburetor. The purpose of the runner is to take advantage of the Helmholtz resonance property of air. Air flows at considerable speed through the open valve. When the valve closes, the air that has not yet entered the valve still has a lot of momentum and compresses against the valve, creating a pocket of high pressure. This high-pressure air begins to equalize with lower-pressure air in the manifold. Due to the air's inertia, the equalization will tend to oscillate: At first the air in the runner will be at a lower pressure than the manifold. The air in the manifold then tries to equalize back into the runner, and the oscillation repeats. This process occurs at the speed of sound, and in most manifolds travels up and down the runner many times before the valve opens again.
The smaller the cross-sectional area of the runner, the higher the pressure changes on resonance for a given airflow. This aspect of Helmholz resonance reproduces one result of the Venturi effect. When the piston accelerates downwards, the pressure at the output of the intake runner is reduced. This low pressure pulse runs to the input end, where it is converted into an over-pressure pulse. This pulse travels back through the runner and rams air through the valve. The valve then closes.
To harness the full power of the Helmholtz resonance effect, the opening of the intake valve must be timed correctly, otherwise the pulse could have a negative effect. This poses a very difficult problem for engines, since valve timing is dynamic and based on engine speed, whereas the pulse timing is static and dependent on the length of the intake runner and the speed of sound. The traditional solution has been to tune the length of the intake runner for a specific engine speed where maximum performance is desired. However, modern technology has given rise to a number of solutions involving electronically controlled valve timing (for example Valvetronic), and dynamic intake geometry (see below).
As a result of "resonance tuning", some naturally aspirated intake systems operate at a volumetric efficiency above 100%: the air pressure in the combustion chamber before the compression stroke is greater than the atmospheric pressure. In combination with this intake manifold design feature, the exhaust manifold design, as well as the exhaust valve opening time can be so calibrated as to achieve greater evacuation of the cylinder. The exhaust manifolds achieve a vacuum in the cylinder just before the piston reaches top dead center.[citation needed] The opening inlet valve can then—at typical compression ratios—fill 10% of the cylinder before beginning downward travel.[citation needed] Instead of achieving higher pressure in the cylinder, the inlet valve can stay open after the piston reaches bottom dead center while the air still flows in.[citation needed][vague]
In some engines the intake runners are straight for minimal resistance. In most engines, however, the runners have curves...and some very convoluted to achieve desired runner length. These turns allow for a more compact manifold, with denser packaging of the whole engine, as a result. Also, these "snaked" runners are needed for some variable length/ split runner designs, and allow the size of the plenum to be reduced. In an engine with at least six cylinders the averaged intake flow is nearly constant and the plenum volume can be smaller. To avoid standing waves within the plenum it is made as compact as possible. The intake runners each use a smaller part of the plenum surface than the inlet, which supplies air to the plenum, for aerodynamic reasons. Each runner is placed to have nearly the same distance to the main inlet. Runners, whose cylinders fire close after each other, are not placed as neighbors.
"180-degree intake manifolds"....Originally designed for carburetor V8 engines, the two plane, split plenum intake manifold separates the intake pulses which the manifold experiences by 180 degrees in the firing order. This minimizes interference of one cylinder's pressure waves with those of another, giving better torque from smooth mid-range flow. Such manifolds may have been originally designed for either two- or four-barrel carburetors, but now are used with both throttle-body and multi-point fuel injection. An example of the latter is the Honda J engine which converts to a single plane manifold around 3500 rpm for greater peak flow and horsepower.
"Heat Riser"....now obsolete, earlier manifolds ...with 'wet runners' for carbureted engines...used exhaust gas diversion through the intake manifold to provide vaporizing heat. The amount of exhaust gas flow diversion was controlled by a heat riser valve in the exhaust manifold, and employed a bi-metallic spring which changed tension according to the heat in the manifold. Today's fuel-injected engines do not require such devices."
Then for a visual on the actual waves, they can be seen in this video, you can see the intake charge blowing back, the air would be traveling at a speed in the 0.55 to 0.60 Mach range.
The highest volumetric efficiency I have heard of is 145%
Good luck with the manifold testing Greg.
In a well tuned engine at the rpm to which it is tuned, the intake valve closing does not cause a meaningful pulse in the intake port or runner.
One way to see why this must be the case is to consider the optimal intake valve closing time. If the engine is well tuned for the rpm at which it's operating, almost by definition the intake valve closes at the optimal time. What is the optimal time? Turns out that the optimal time is before the air has started moving backwards but after it no longer is moving forward -- that is, when the air is not moving in either direction at the valve. Any closing the valve earlier would reduce the cylinder filling, as would any closing of the valve later, hence it's the optimal timing. If the intake valve is closed at the optimal time when air is not moving at the valve, then valve closing can't cause any "inertia" pulse either. Thus, the common belief that air column hitting a closed valve causes the pulse is wrong, at least for well tuned engines.
What causes the pulse then? It's my understanding that the pressure wave is caused by the piston first decelerating before the BDC and then moving up in the cylinder. The piston moving up in the cylinder combined with the inertia of the air column moving down causes a pressure increase in the cylinder. The pressure increase spreads upstream thru the port and imposes a force on the air column, decelerating it. The air column stops when the pressure force overcomes the air column inertia, at which point the pressure in the intake port is quite high. The valve closes at that optimal point, but this doesn't cause a pulse. Rather, the high pressure that _is_ the pulse is already in the port and around the valve when the valve closes. The pressure wave travels up the runner (and in an isolated runner single plenum manifold will be reflected back as rarefaction wave towards the valve, etc.)
The 1D simulators appear consistent with this, as they show a strong pulse even when the intake valve is closed exactly at the optimal time when the local air speed at the valve is zero. The wave starts building as the piston approaches the BDC.
At least this is how I've understood it to work out.
One way to see why this must be the case is to consider the optimal intake valve closing time. If the engine is well tuned for the rpm at which it's operating, almost by definition the intake valve closes at the optimal time. What is the optimal time? Turns out that the optimal time is before the air has started moving backwards but after it no longer is moving forward -- that is, when the air is not moving in either direction at the valve. Any closing the valve earlier would reduce the cylinder filling, as would any closing of the valve later, hence it's the optimal timing. If the intake valve is closed at the optimal time when air is not moving at the valve, then valve closing can't cause any "inertia" pulse either. Thus, the common belief that air column hitting a closed valve causes the pulse is wrong, at least for well tuned engines.
What causes the pulse then? It's my understanding that the pressure wave is caused by the piston first decelerating before the BDC and then moving up in the cylinder. The piston moving up in the cylinder combined with the inertia of the air column moving down causes a pressure increase in the cylinder. The pressure increase spreads upstream thru the port and imposes a force on the air column, decelerating it. The air column stops when the pressure force overcomes the air column inertia, at which point the pressure in the intake port is quite high. The valve closes at that optimal point, but this doesn't cause a pulse. Rather, the high pressure that _is_ the pulse is already in the port and around the valve when the valve closes. The pressure wave travels up the runner (and in an isolated runner single plenum manifold will be reflected back as rarefaction wave towards the valve, etc.)
The 1D simulators appear consistent with this, as they show a strong pulse even when the intake valve is closed exactly at the optimal time when the local air speed at the valve is zero. The wave starts building as the piston approaches the BDC.
At least this is how I've understood it to work out.
04-21-2013, 07:14 PM
#54
Former Vendor
Thread Starter
I think that this explanation from Wikipedia is a good one;
"The design and orientation of the intake manifold is a major factor in the volumetric efficiency of an engine. Abrupt contour changes provoke pressure drops, resulting in less air (and/or fuel) entering the combustion chamber; high-performance manifolds have smooth contours and gradual transitions between adjacent segments.
Modern intake manifolds usually employ runners, individual tubes extending to each intake port on the cylinder head which emanate from a central volume or "plenum" beneath the carburetor. The purpose of the runner is to take advantage of the Helmholtz resonance property of air. Air flows at considerable speed through the open valve. When the valve closes, the air that has not yet entered the valve still has a lot of momentum and compresses against the valve, creating a pocket of high pressure. This high-pressure air begins to equalize with lower-pressure air in the manifold. Due to the air's inertia, the equalization will tend to oscillate: At first the air in the runner will be at a lower pressure than the manifold. The air in the manifold then tries to equalize back into the runner, and the oscillation repeats. This process occurs at the speed of sound, and in most manifolds travels up and down the runner many times before the valve opens again.
The smaller the cross-sectional area of the runner, the higher the pressure changes on resonance for a given airflow. This aspect of Helmholz resonance reproduces one result of the Venturi effect. When the piston accelerates downwards, the pressure at the output of the intake runner is reduced. This low pressure pulse runs to the input end, where it is converted into an over-pressure pulse. This pulse travels back through the runner and rams air through the valve. The valve then closes.
To harness the full power of the Helmholtz resonance effect, the opening of the intake valve must be timed correctly, otherwise the pulse could have a negative effect. This poses a very difficult problem for engines, since valve timing is dynamic and based on engine speed, whereas the pulse timing is static and dependent on the length of the intake runner and the speed of sound. The traditional solution has been to tune the length of the intake runner for a specific engine speed where maximum performance is desired. However, modern technology has given rise to a number of solutions involving electronically controlled valve timing (for example Valvetronic), and dynamic intake geometry (see below).
As a result of "resonance tuning", some naturally aspirated intake systems operate at a volumetric efficiency above 100%: the air pressure in the combustion chamber before the compression stroke is greater than the atmospheric pressure. In combination with this intake manifold design feature, the exhaust manifold design, as well as the exhaust valve opening time can be so calibrated as to achieve greater evacuation of the cylinder. The exhaust manifolds achieve a vacuum in the cylinder just before the piston reaches top dead center.[citation needed] The opening inlet valve can then—at typical compression ratios—fill 10% of the cylinder before beginning downward travel.[citation needed] Instead of achieving higher pressure in the cylinder, the inlet valve can stay open after the piston reaches bottom dead center while the air still flows in.[citation needed][vague]
In some engines the intake runners are straight for minimal resistance. In most engines, however, the runners have curves...and some very convoluted to achieve desired runner length. These turns allow for a more compact manifold, with denser packaging of the whole engine, as a result. Also, these "snaked" runners are needed for some variable length/ split runner designs, and allow the size of the plenum to be reduced. In an engine with at least six cylinders the averaged intake flow is nearly constant and the plenum volume can be smaller. To avoid standing waves within the plenum it is made as compact as possible. The intake runners each use a smaller part of the plenum surface than the inlet, which supplies air to the plenum, for aerodynamic reasons. Each runner is placed to have nearly the same distance to the main inlet. Runners, whose cylinders fire close after each other, are not placed as neighbors.
"180-degree intake manifolds"....Originally designed for carburetor V8 engines, the two plane, split plenum intake manifold separates the intake pulses which the manifold experiences by 180 degrees in the firing order. This minimizes interference of one cylinder's pressure waves with those of another, giving better torque from smooth mid-range flow. Such manifolds may have been originally designed for either two- or four-barrel carburetors, but now are used with both throttle-body and multi-point fuel injection. An example of the latter is the Honda J engine which converts to a single plane manifold around 3500 rpm for greater peak flow and horsepower.
"Heat Riser"....now obsolete, earlier manifolds ...with 'wet runners' for carbureted engines...used exhaust gas diversion through the intake manifold to provide vaporizing heat. The amount of exhaust gas flow diversion was controlled by a heat riser valve in the exhaust manifold, and employed a bi-metallic spring which changed tension according to the heat in the manifold. Today's fuel-injected engines do not require such devices."
Then for a visual on the actual waves, they can be seen in this video, you can see the intake charge blowing back, the air would be traveling at a speed in the 0.55 to 0.60 Mach range.
The highest volumetric efficiency I have heard of is 145%
Renault F1 Engine - YouTube
Good luck with the manifold testing Greg.
"The design and orientation of the intake manifold is a major factor in the volumetric efficiency of an engine. Abrupt contour changes provoke pressure drops, resulting in less air (and/or fuel) entering the combustion chamber; high-performance manifolds have smooth contours and gradual transitions between adjacent segments.
Modern intake manifolds usually employ runners, individual tubes extending to each intake port on the cylinder head which emanate from a central volume or "plenum" beneath the carburetor. The purpose of the runner is to take advantage of the Helmholtz resonance property of air. Air flows at considerable speed through the open valve. When the valve closes, the air that has not yet entered the valve still has a lot of momentum and compresses against the valve, creating a pocket of high pressure. This high-pressure air begins to equalize with lower-pressure air in the manifold. Due to the air's inertia, the equalization will tend to oscillate: At first the air in the runner will be at a lower pressure than the manifold. The air in the manifold then tries to equalize back into the runner, and the oscillation repeats. This process occurs at the speed of sound, and in most manifolds travels up and down the runner many times before the valve opens again.
The smaller the cross-sectional area of the runner, the higher the pressure changes on resonance for a given airflow. This aspect of Helmholz resonance reproduces one result of the Venturi effect. When the piston accelerates downwards, the pressure at the output of the intake runner is reduced. This low pressure pulse runs to the input end, where it is converted into an over-pressure pulse. This pulse travels back through the runner and rams air through the valve. The valve then closes.
To harness the full power of the Helmholtz resonance effect, the opening of the intake valve must be timed correctly, otherwise the pulse could have a negative effect. This poses a very difficult problem for engines, since valve timing is dynamic and based on engine speed, whereas the pulse timing is static and dependent on the length of the intake runner and the speed of sound. The traditional solution has been to tune the length of the intake runner for a specific engine speed where maximum performance is desired. However, modern technology has given rise to a number of solutions involving electronically controlled valve timing (for example Valvetronic), and dynamic intake geometry (see below).
As a result of "resonance tuning", some naturally aspirated intake systems operate at a volumetric efficiency above 100%: the air pressure in the combustion chamber before the compression stroke is greater than the atmospheric pressure. In combination with this intake manifold design feature, the exhaust manifold design, as well as the exhaust valve opening time can be so calibrated as to achieve greater evacuation of the cylinder. The exhaust manifolds achieve a vacuum in the cylinder just before the piston reaches top dead center.[citation needed] The opening inlet valve can then—at typical compression ratios—fill 10% of the cylinder before beginning downward travel.[citation needed] Instead of achieving higher pressure in the cylinder, the inlet valve can stay open after the piston reaches bottom dead center while the air still flows in.[citation needed][vague]
In some engines the intake runners are straight for minimal resistance. In most engines, however, the runners have curves...and some very convoluted to achieve desired runner length. These turns allow for a more compact manifold, with denser packaging of the whole engine, as a result. Also, these "snaked" runners are needed for some variable length/ split runner designs, and allow the size of the plenum to be reduced. In an engine with at least six cylinders the averaged intake flow is nearly constant and the plenum volume can be smaller. To avoid standing waves within the plenum it is made as compact as possible. The intake runners each use a smaller part of the plenum surface than the inlet, which supplies air to the plenum, for aerodynamic reasons. Each runner is placed to have nearly the same distance to the main inlet. Runners, whose cylinders fire close after each other, are not placed as neighbors.
"180-degree intake manifolds"....Originally designed for carburetor V8 engines, the two plane, split plenum intake manifold separates the intake pulses which the manifold experiences by 180 degrees in the firing order. This minimizes interference of one cylinder's pressure waves with those of another, giving better torque from smooth mid-range flow. Such manifolds may have been originally designed for either two- or four-barrel carburetors, but now are used with both throttle-body and multi-point fuel injection. An example of the latter is the Honda J engine which converts to a single plane manifold around 3500 rpm for greater peak flow and horsepower.
"Heat Riser"....now obsolete, earlier manifolds ...with 'wet runners' for carbureted engines...used exhaust gas diversion through the intake manifold to provide vaporizing heat. The amount of exhaust gas flow diversion was controlled by a heat riser valve in the exhaust manifold, and employed a bi-metallic spring which changed tension according to the heat in the manifold. Today's fuel-injected engines do not require such devices."
Then for a visual on the actual waves, they can be seen in this video, you can see the intake charge blowing back, the air would be traveling at a speed in the 0.55 to 0.60 Mach range.
The highest volumetric efficiency I have heard of is 145%
Renault F1 Engine - YouTube
Good luck with the manifold testing Greg.
However, the theory isn't important...what happens is what really matters. And "inertia supercharging" actually does occur.
I've got a good friend that owns his own dyno....no flow bench, no other tools. He points at his dyno and says: "That's my flow bench...everything else is just theory."
I believe that with the "inflated" dyno results that we are subjected to, today, it is common for people to "think/wish" they were getting volumetric efficiency, regularly, in the 145% range. However, I believe the number to be more in the 120% range.....and that is very rare cases on extremely well engineered and tuned high performance engines.
04-21-2013, 07:50 PM
#55
Greg, we know there is plenty of inflated dyno numbers around, however that 145% did come from Cosworth in regard to their F1 engine. I really doubt any sort of two valve engine or most 4 valve engines can get near that unless it maybe is a Pro Stock engine that runs for around 6 seconds, most 928 owners would be saying warranty please at 10 seconds.
On another note and I don't have a program to work out it's ball park efficiency, a Honda engine, (street driven) 2.5 liter at 8,000 rpm did 313 rwhp on a dynopak dyno at the axles. So it efficiency would be quite high, like around that 120% you quoted.
On another note and I don't have a program to work out it's ball park efficiency, a Honda engine, (street driven) 2.5 liter at 8,000 rpm did 313 rwhp on a dynopak dyno at the axles. So it efficiency would be quite high, like around that 120% you quoted.
This explanation is what I've always understood to be happening. I find Ptuomov's explanation different, interesting, and worth thinking about.
However, the theory isn't important...what happens is what really matters. And "inertia supercharging" actually does occur.
I've got a good friend that owns his own dyno....no flow bench, no other tools. He points at his dyno and says: "That's my flow bench...everything else is just theory."
I believe that with the "inflated" dyno results that we are subjected to, today, it is common for people to "think/wish" they were getting volumetric efficiency, regularly, in the 145% range. However, I believe the number to be more in the 120% range.....and that is very rare cases on extremely well engineered and tuned high performance engines.
However, the theory isn't important...what happens is what really matters. And "inertia supercharging" actually does occur.
I've got a good friend that owns his own dyno....no flow bench, no other tools. He points at his dyno and says: "That's my flow bench...everything else is just theory."
I believe that with the "inflated" dyno results that we are subjected to, today, it is common for people to "think/wish" they were getting volumetric efficiency, regularly, in the 145% range. However, I believe the number to be more in the 120% range.....and that is very rare cases on extremely well engineered and tuned high performance engines.
04-21-2013, 08:12 PM
#56
Former Vendor
Thread Starter
Greg, we know there is plenty of inflated dyno numbers around, however that 145% did come from Cosworth in regard to their F1 engine. I really doubt any sort of two valve engine or most 4 valve engines can get near that unless it maybe is a Pro Stock engine that runs for around 6 seconds, most 928 owners would be saying warranty please at 10 seconds.
On another note and I don't have a program to work out it's ball park efficiency, a Honda engine, (street driven) 2.5 liter at 8,000 rpm did 313 rwhp on a dynopak dyno at the axles. So it efficiency would be quite high, like around that 120% you quoted.
On another note and I don't have a program to work out it's ball park efficiency, a Honda engine, (street driven) 2.5 liter at 8,000 rpm did 313 rwhp on a dynopak dyno at the axles. So it efficiency would be quite high, like around that 120% you quoted.
The mid 1970s were a very "low" point for both of these things....and great improvements have been made.
How much power did a stock Chevy 454 make in 1974 and what was the gas mileage?
What year do you suppose the 928 engine was developed?
I'm always pleased at what "smog" numbers I get back for my "stroker" engines. It is common for these engines to register near zero on the smog tests and get 3-4 more miles per gallon, cruising around, than a stock engine.
04-21-2013, 09:31 PM
#58
Former Vendor
Thread Starter
When we stick the "Beta Version" onto a 5.0 engine, that will be "on the engine dyno", like your engine was. We are planning on building a "higher rpm" 5.0 engine.
Do you have any RWHP dyno stuff that you have done there, for your own car? I have engine data, from the DTS sessions, but nothing for RWHP.
04-21-2013, 09:38 PM
#59
Very interesting. No BS on this one.
04-21-2013, 09:49 PM
#60
Nordschleife Master
I think that this explanation from Wikipedia is a good one;
"Modern intake manifolds usually employ runners, individual tubes extending to each intake port on the cylinder head which emanate from a central volume or "plenum" beneath the carburetor. The purpose of the runner is to take advantage of the Helmholtz resonance property of air. Air flows at considerable speed through the open valve. When the valve closes, the air that has not yet entered the valve still has a lot of momentum and compresses against the valve, creating a pocket of high pressure. This high-pressure air begins to equalize with lower-pressure air in the manifold. Due to the air's inertia, the equalization will tend to oscillate: At first the air in the runner will be at a lower pressure than the manifold. The air in the manifold then tries to equalize back into the runner, and the oscillation repeats. This process occurs at the speed of sound, and in most manifolds travels up and down the runner many times before the valve opens again."
"Modern intake manifolds usually employ runners, individual tubes extending to each intake port on the cylinder head which emanate from a central volume or "plenum" beneath the carburetor. The purpose of the runner is to take advantage of the Helmholtz resonance property of air. Air flows at considerable speed through the open valve. When the valve closes, the air that has not yet entered the valve still has a lot of momentum and compresses against the valve, creating a pocket of high pressure. This high-pressure air begins to equalize with lower-pressure air in the manifold. Due to the air's inertia, the equalization will tend to oscillate: At first the air in the runner will be at a lower pressure than the manifold. The air in the manifold then tries to equalize back into the runner, and the oscillation repeats. This process occurs at the speed of sound, and in most manifolds travels up and down the runner many times before the valve opens again."
For an engine operating with the optimal intake valve closing point, the air at the valve is not moving in either direction when the valve closes. If it were still moving towards the cylinder, you'd make more power by keeping the valve open a bit longer -- air is still going into the cylinder!
Not all manifolds, or even most manifolds, use the Helmholtz effect. Unless you get really technical and call the cylinder the Helmholtz resonator, but that's not what they mean.
The pressure wave reflected from the cylinder near the piston BDC is a pressure wave and it's reflected from the runner mouth as a rarefaction wave in most manifolds. Increases in the cross-sectional area reflect a wave of opposite sign, while decreases in the cross-sectional area reflect a wave of the same sign.
The waves don't move at the speed of sound relative to the runner, they move at the speed that combines the speed of the air in the runner and the speed of the wave in the air. The wave theory that is predictive in engines is the finite wave theory, while the harmonic wave theory really isn't.
I am not pretending to be the authority on the topic, all I am saying that I can't personally make sense of much of what I read from that Wikipedia article. That says something about me and/or the Wikipedia article but what exactly it says is everyone's own judgement.