Ram Air is a Myth.
10-26-2004, 10:36 PM
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Ram Air is a Myth.
Dispelling the Myth about "Ram Air" in Automobiles
There are many air intakes on the market today. Many claim "superior" performance over others.
Air intakes can be seperated into specific catagories:
- Those that take in warm engine bay air
- Those that are exposed to cooler/fresher air from the front.
The biggest bennefit of adding an aftermarket air intake is unshrouding the factory air box.
The last bennefit is exposing it to fresh air.
Ram Air is a myth, and many intake manufactures use the word Ram Air strictly for propaganda. They also try to show track results compared to other intakes that simply incur too many variables to make a meaningful and empirical determination. 60 foot times, atmospheric changes, shifting, etc, etc. So do not beleive anything you hear regarding such claims regarding air intakes.
Lets take a look at the "Ram Air" Myth in automobiles:
The Ram Air Myth by Dave Rodabaugh
The Ram Air Myth is the most mythical of them all. It differs from the other myths, in that the other myths are misinterpretations of physical phenomena, whereas ram air simply does not exist.
MYTH: Use of a scoop on the front of the vehicle to collect intake air, or provide “ram air” can raise engine performance.
TRUTH: At automobile velocities, there is no ram air effect.
SIMPLE EXPLANATION
The "Truth" statement says it all. How much simpler can it be? The Ram Air effect is a total myth because it simply does not exist. “But Pontiac uses it on the Trans Am, and they know more than you do.” To those who offer this, tsk tsk. Careful reading of Pontiac’s statements on the matter reveal that the HP increase of the WS6 package are a result of a less restrictive intake, and a freer-flowing exhaust, NOT any ram air effect.
So why does Pontiac use Ram Air? Easy! To make people buy their cars! And they are quite effective with this strategy.
DEEPER EXPLANATION
Of all of the applied sciences, fluid mechanics is among the most difficult for many people to comprehend. It is a relatively youthful applied science as well, meaning that it has not had two or three centuries of work to mature into an applied science on par, with say, chemical combustion. To make matters worse, it is mathematically defined almost entirely by experimentally-determined mathematics.
This last point is the true differentiator between those who only understand concepts, and those who can quantify what they are discussing. Truly, quantification is the real skill of the engineer. It is one thing to speak about qualitative issues (the “what” of the physical sciences); it is entirely another to quantify them (the “how much” and “to what extent” of the same). In grade school, students are first taught about “closed form mathematics” and then that these mathematics are typical of scientific expression. A good example of this is Newton’s famed “law of action and reaction”, the mathematical expression of which is a succinct F=MA. So straightforward. So simple. Three variables in perfectly-defined harmony. Given any two of them, the third is easy to nail down.
Unfortunately, a vast, vast majority of the mathematics used in engineering are NOT closed form. Instead, they are multi-variable correlations valid only for a narrow set of circumstances. Deviate from those narrow circumstances, and a new expression must be experimentally derived. Fluid mechanics is almost entirely defined by these experimentally-determined expressions, further muddying an applied science not well understood.
And if there ever were an applied science for which common sense is wholly inappropriate, it is fluid mechanics. Virtually nothing obeys the “common sense” rules of observation, explaining why those who believe in ram air have extreme difficulty in believing that is simply does not exist.
The Deeper Explanation begins with a basic explanation of engine principles. Air and fuel must be combusted at a specific ratio, namely, 14.7 parts air to 1 part fuel (this is a chemical ratio). Stuffing more fuel into the cylinders without increasing the amount of air they also swallow will get no gain whatsoever. So the hot rodder’s adage “more air = more power” is proven correct. Figure out a way to stuff more air into the cylinder at any given RPM and throttle setting, and you can burn more fuel. Since burning fuel is what makes power, more air truly does create more power.
The amount of air which is inducted into a cylinder is a function of the air’s density. As the air flows through the intake tract, it loses pressure, and as the pressure decreases, so does the air’s density. (Denisty is mass divided by volume. Since cylinders are a fixed volume, increasing the density will also increase the mass of the air in the cylinder.) There are two ways to increase the pressure and density of the air inducted into the cylinders:
- Decrease the pressure drop from the throttle plate to the cylinders
- Increase the starting pressure at the throttle plate.
Ram air is an attempt to do the second. Under normal circumstances, the air at the throttle plate is at atmospheric pressure, and this pressure drops until the air reaches the cylinders. Ram air would start the process at some pressure higher than atmospheric, and even though the drop is the same, the cylinder pressure is higher because of the increase at the start.
Just how would this increase in pressure at the throttle plate occur? The oft-wrong “common sense” says, “If a scoop is placed in the airstream flowing around the vehicle, the velocity of the air ‘rams’ the air into the scoop, thus increasing the pressure.”
Why is this incorrect? There are two types of pressure: static and dynamic. Placing of one’s hand in front of a fan, or out of a moving car’s window, clearly exerts a force on the hand as the air diverts its path to flow around it. Most people would say “See? This is a clear indication that ram air works. Clearly there is pressure from the velocity of the air.” Well, this is correct, but only to a point. This is an example of dynamic pressure, or the force any moving fluid exerts upon obstacles in its path as the gas is diverted around the obstacle.
What an engine needs is static pressure. This is the pressure the same fluid exerts on any vessel containing it at rest. For those who were physics/chemistry geeks, it is the pressure caused by the force of the molecules bouncing off of the walls of the container. The key to understanding the difference between static and dynamic pressure lies in the velocity of the gas. Dynamic pressure is only a momentum effect due to the bulk motion of the fluid around an obstacle. Static pressure is an intrinsic property of a gas or fluid just because the molecules of the fluid are moving around. Any fluid which is moving can have BOTH dynamic and static pressure, but a fluid at rest only has static pressure.
The point of ram air would be to increase the static pressure, which would correspond to an increase in the in-cylinder air density, and of course, more air. Superchargers and turbochargers do what the mythical ram air purports to do. A supercharger trades the power of the belt and uses it to compress the air in the intake tract. This energy trade-off results in an increase in intake air pressure, more air in the cylinders, more fuel burned, and more power. A turbocharger trades the power of the hot gases and uses it to compress the air in the intake. The overall effect is the same – an increase in intake static pressure.
For ram air to work, it would have to trade the energy of the air’s velocity (as the vehicle moves through the air) for an increase in static pressure (since static pressure is a part of a gas’s internal energy, we see this is TRULY a trade in kinetic energy for an increase in internal energy). Now for the true reasons why ram air is a myth:
- The way for air velocity to be traded for an increase in static pressure is to actually SLOW IT DOWN in a nozzle of some sort. This is easily the MOST counterintuitive part of fluid mechanics for most people. The “common sense” mind says “In order to increase the pressure of the intake, the velocity of the air needs to be increased, just as increasing the speed of a fan exerts more force upon the hand.” Not only does this confuse dynamic with static pressure, but is also misses the point, which is to trade the kinetic energy of the gas for an increase in internal energy. How can this trade occur if the kinetic energy of the gas is increased? It cannot, and in fact, the only way to trade it is to use the velocity of the gas to compress itself – by slowing it down.
- Below about Mach 0.5 (or about half the speed of sound), air is considered “incompressible”. That is, even if the correct nozzle is selected, and the air is slowed down (the official term is “stagnated”) there will be zero trade. No kinetic energy will be traded in as work capable of compressing the air. The reasons for this are not discussed here; the reader may consult any reputable fluid mechanics textbook for confirmation of this fact. In plain English, a car is just too slow for ram air to work.
Still not enough evidence? Here is a little test. For ram air to work, the nozzle must be of a specific shape. The “Holley Scoop” for the Fiero is the wrong shape, by the way. The fact that it has no net shape at all immediately means it cannot effect any kind of energy trade off, so it cannot possibly create ram air. This is also true for the hood scoops on the Pontiac Firebird WS6 package as well, by the way.
What shape must it be? There are two kinds of nozzles. Pick one:
- Converging. This nozzle gets smaller as the air flows through it. It has a smaller exit than entrance. If the nozzle were a cone, the fat end is where the air would enter, and the narrow end is where it would exit.
- Diverging. This nozzle is opposite the other; it gets bigger as the air flows through it. With a larger exit than entrance, the narrow end of the cone is where the air would enter, and the fat end is where it would exit.
So, which is it?
Without hesitation, most of the “common sense” crowd will answer “Converging.” BZZZZT! Thank you for playing anyway! We have some lovely parting gifts for you! Bill, tell ‘em what they’ve won….
The answer is “divergent”. Yes, the nozzle would have to shaped so that the skinny end is pointed into the air stream, and the fat end connects to the throttle plate. How can this be right? Remember, to increase the static pressure of the intake air (which is the true “ram air” effect), the kinetic energy of the air must be traded to compress the air. This is done by slowing the air down, or stagnating it, and the only way to do this is with a diverging nozzle. Ah, but since air is incompressible at automobile speeds, it doesn’t matter any way.
Conclusion
Ram air is a myth because it does not exist, for the following reasons:
- Air is incompressible at any automobile speed., meaning that the kinetic energy of the air cannot be used to compress the air and raise the static pressure.
- The “ram air” nozzles commonly employed on automobiles tend to be the wrong shape. A divergent nozzle is required for ram air. Straight-profile scoops cannot provide a ram air effect.
Select one of the two types of intakes, warm air, or cold air. Beyond that its just about looks.
-Thanks to http://www.vetteguru.com/ramair/ for the info
There are many air intakes on the market today. Many claim "superior" performance over others.
Air intakes can be seperated into specific catagories:
- Those that take in warm engine bay air
- Those that are exposed to cooler/fresher air from the front.
The biggest bennefit of adding an aftermarket air intake is unshrouding the factory air box.
The last bennefit is exposing it to fresh air.
Ram Air is a myth, and many intake manufactures use the word Ram Air strictly for propaganda. They also try to show track results compared to other intakes that simply incur too many variables to make a meaningful and empirical determination. 60 foot times, atmospheric changes, shifting, etc, etc. So do not beleive anything you hear regarding such claims regarding air intakes.
Lets take a look at the "Ram Air" Myth in automobiles:
The Ram Air Myth by Dave Rodabaugh
The Ram Air Myth is the most mythical of them all. It differs from the other myths, in that the other myths are misinterpretations of physical phenomena, whereas ram air simply does not exist.
MYTH: Use of a scoop on the front of the vehicle to collect intake air, or provide “ram air” can raise engine performance.
TRUTH: At automobile velocities, there is no ram air effect.
SIMPLE EXPLANATION
The "Truth" statement says it all. How much simpler can it be? The Ram Air effect is a total myth because it simply does not exist. “But Pontiac uses it on the Trans Am, and they know more than you do.” To those who offer this, tsk tsk. Careful reading of Pontiac’s statements on the matter reveal that the HP increase of the WS6 package are a result of a less restrictive intake, and a freer-flowing exhaust, NOT any ram air effect.
So why does Pontiac use Ram Air? Easy! To make people buy their cars! And they are quite effective with this strategy.
DEEPER EXPLANATION
Of all of the applied sciences, fluid mechanics is among the most difficult for many people to comprehend. It is a relatively youthful applied science as well, meaning that it has not had two or three centuries of work to mature into an applied science on par, with say, chemical combustion. To make matters worse, it is mathematically defined almost entirely by experimentally-determined mathematics.
This last point is the true differentiator between those who only understand concepts, and those who can quantify what they are discussing. Truly, quantification is the real skill of the engineer. It is one thing to speak about qualitative issues (the “what” of the physical sciences); it is entirely another to quantify them (the “how much” and “to what extent” of the same). In grade school, students are first taught about “closed form mathematics” and then that these mathematics are typical of scientific expression. A good example of this is Newton’s famed “law of action and reaction”, the mathematical expression of which is a succinct F=MA. So straightforward. So simple. Three variables in perfectly-defined harmony. Given any two of them, the third is easy to nail down.
Unfortunately, a vast, vast majority of the mathematics used in engineering are NOT closed form. Instead, they are multi-variable correlations valid only for a narrow set of circumstances. Deviate from those narrow circumstances, and a new expression must be experimentally derived. Fluid mechanics is almost entirely defined by these experimentally-determined expressions, further muddying an applied science not well understood.
And if there ever were an applied science for which common sense is wholly inappropriate, it is fluid mechanics. Virtually nothing obeys the “common sense” rules of observation, explaining why those who believe in ram air have extreme difficulty in believing that is simply does not exist.
The Deeper Explanation begins with a basic explanation of engine principles. Air and fuel must be combusted at a specific ratio, namely, 14.7 parts air to 1 part fuel (this is a chemical ratio). Stuffing more fuel into the cylinders without increasing the amount of air they also swallow will get no gain whatsoever. So the hot rodder’s adage “more air = more power” is proven correct. Figure out a way to stuff more air into the cylinder at any given RPM and throttle setting, and you can burn more fuel. Since burning fuel is what makes power, more air truly does create more power.
The amount of air which is inducted into a cylinder is a function of the air’s density. As the air flows through the intake tract, it loses pressure, and as the pressure decreases, so does the air’s density. (Denisty is mass divided by volume. Since cylinders are a fixed volume, increasing the density will also increase the mass of the air in the cylinder.) There are two ways to increase the pressure and density of the air inducted into the cylinders:
- Decrease the pressure drop from the throttle plate to the cylinders
- Increase the starting pressure at the throttle plate.
Ram air is an attempt to do the second. Under normal circumstances, the air at the throttle plate is at atmospheric pressure, and this pressure drops until the air reaches the cylinders. Ram air would start the process at some pressure higher than atmospheric, and even though the drop is the same, the cylinder pressure is higher because of the increase at the start.
Just how would this increase in pressure at the throttle plate occur? The oft-wrong “common sense” says, “If a scoop is placed in the airstream flowing around the vehicle, the velocity of the air ‘rams’ the air into the scoop, thus increasing the pressure.”
Why is this incorrect? There are two types of pressure: static and dynamic. Placing of one’s hand in front of a fan, or out of a moving car’s window, clearly exerts a force on the hand as the air diverts its path to flow around it. Most people would say “See? This is a clear indication that ram air works. Clearly there is pressure from the velocity of the air.” Well, this is correct, but only to a point. This is an example of dynamic pressure, or the force any moving fluid exerts upon obstacles in its path as the gas is diverted around the obstacle.
What an engine needs is static pressure. This is the pressure the same fluid exerts on any vessel containing it at rest. For those who were physics/chemistry geeks, it is the pressure caused by the force of the molecules bouncing off of the walls of the container. The key to understanding the difference between static and dynamic pressure lies in the velocity of the gas. Dynamic pressure is only a momentum effect due to the bulk motion of the fluid around an obstacle. Static pressure is an intrinsic property of a gas or fluid just because the molecules of the fluid are moving around. Any fluid which is moving can have BOTH dynamic and static pressure, but a fluid at rest only has static pressure.
The point of ram air would be to increase the static pressure, which would correspond to an increase in the in-cylinder air density, and of course, more air. Superchargers and turbochargers do what the mythical ram air purports to do. A supercharger trades the power of the belt and uses it to compress the air in the intake tract. This energy trade-off results in an increase in intake air pressure, more air in the cylinders, more fuel burned, and more power. A turbocharger trades the power of the hot gases and uses it to compress the air in the intake. The overall effect is the same – an increase in intake static pressure.
For ram air to work, it would have to trade the energy of the air’s velocity (as the vehicle moves through the air) for an increase in static pressure (since static pressure is a part of a gas’s internal energy, we see this is TRULY a trade in kinetic energy for an increase in internal energy). Now for the true reasons why ram air is a myth:
- The way for air velocity to be traded for an increase in static pressure is to actually SLOW IT DOWN in a nozzle of some sort. This is easily the MOST counterintuitive part of fluid mechanics for most people. The “common sense” mind says “In order to increase the pressure of the intake, the velocity of the air needs to be increased, just as increasing the speed of a fan exerts more force upon the hand.” Not only does this confuse dynamic with static pressure, but is also misses the point, which is to trade the kinetic energy of the gas for an increase in internal energy. How can this trade occur if the kinetic energy of the gas is increased? It cannot, and in fact, the only way to trade it is to use the velocity of the gas to compress itself – by slowing it down.
- Below about Mach 0.5 (or about half the speed of sound), air is considered “incompressible”. That is, even if the correct nozzle is selected, and the air is slowed down (the official term is “stagnated”) there will be zero trade. No kinetic energy will be traded in as work capable of compressing the air. The reasons for this are not discussed here; the reader may consult any reputable fluid mechanics textbook for confirmation of this fact. In plain English, a car is just too slow for ram air to work.
Still not enough evidence? Here is a little test. For ram air to work, the nozzle must be of a specific shape. The “Holley Scoop” for the Fiero is the wrong shape, by the way. The fact that it has no net shape at all immediately means it cannot effect any kind of energy trade off, so it cannot possibly create ram air. This is also true for the hood scoops on the Pontiac Firebird WS6 package as well, by the way.
What shape must it be? There are two kinds of nozzles. Pick one:
- Converging. This nozzle gets smaller as the air flows through it. It has a smaller exit than entrance. If the nozzle were a cone, the fat end is where the air would enter, and the narrow end is where it would exit.
- Diverging. This nozzle is opposite the other; it gets bigger as the air flows through it. With a larger exit than entrance, the narrow end of the cone is where the air would enter, and the fat end is where it would exit.
So, which is it?
Without hesitation, most of the “common sense” crowd will answer “Converging.” BZZZZT! Thank you for playing anyway! We have some lovely parting gifts for you! Bill, tell ‘em what they’ve won….
The answer is “divergent”. Yes, the nozzle would have to shaped so that the skinny end is pointed into the air stream, and the fat end connects to the throttle plate. How can this be right? Remember, to increase the static pressure of the intake air (which is the true “ram air” effect), the kinetic energy of the air must be traded to compress the air. This is done by slowing the air down, or stagnating it, and the only way to do this is with a diverging nozzle. Ah, but since air is incompressible at automobile speeds, it doesn’t matter any way.
Conclusion
Ram air is a myth because it does not exist, for the following reasons:
- Air is incompressible at any automobile speed., meaning that the kinetic energy of the air cannot be used to compress the air and raise the static pressure.
- The “ram air” nozzles commonly employed on automobiles tend to be the wrong shape. A divergent nozzle is required for ram air. Straight-profile scoops cannot provide a ram air effect.
Select one of the two types of intakes, warm air, or cold air. Beyond that its just about looks.
-Thanks to http://www.vetteguru.com/ramair/ for the info
10-26-2004, 10:48 PM
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The only way to "ram" more air into an engine is through boost via super/turbo. Everyone knows this. He could have saved a lot of space by leaving out all that written masturbation.
10-26-2004, 10:54 PM
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Hmm. I'm going to have to rig up a MAF or get a boost guage and see what real gains in terms of airflow I am really getting with my 'ram air.'
Great reading, thanks!
EDIT: oh, and I dont think it matters too much about the scoop, because the diamater changes as soon as the air passes through the carb/tb. Long as the scoop is larger than that, it does compress, er, right?
Great reading, thanks!
EDIT: oh, and I dont think it matters too much about the scoop, because the diamater changes as soon as the air passes through the carb/tb. Long as the scoop is larger than that, it does compress, er, right?
Last edited by 305q_ta86; 10-26-2004 at 10:58 PM.
10-26-2004, 11:02 PM
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Would it be incorrect to believe that the said "Ram Air" intake might be better due to the fact that air has a more direct route to the engine in this sort of setup, compared to a "cold air intake" where it must travel less directly through a series of bends?
10-26-2004, 11:04 PM
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10-26-2004, 11:05 PM
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Ram air is not a myth!! Its effect is just negligible at speeds automobiles generally travel at. Ram air is exactly how Ram jet engines work.
10-26-2004, 11:12 PM
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Originally posted by ME Leigh
Ram air is not a myth!! Its effect is just negligible at speeds automobiles generally travel at. Ram air is exactly how Ram jet engines work.
Ram air is not a myth!! Its effect is just negligible at speeds automobiles generally travel at. Ram air is exactly how Ram jet engines work.
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10-26-2004, 11:15 PM
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Yup, believe you need to be hitting somewhere around 300mph to get any "ram air" effect. Its a marketing gimmick, all it ever was.
10-26-2004, 11:15 PM
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Originally posted by ME Leigh
Ram air is not a myth!! Its effect is just negligible at speeds automobiles generally travel at.
Ram air is not a myth!! Its effect is just negligible at speeds automobiles generally travel at.
10-26-2004, 11:18 PM
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... so does this also mean that a rear facing scoop, like a cowl hood, should theoretically have almost the exact same performance gains as in a forward facing scoop?
10-26-2004, 11:31 PM
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Originally posted by 305q_ta86
... so does this also mean that a rear facing scoop, like a cowl hood, should theoretically have almost the exact same performance gains as in a forward facing scoop?
... so does this also mean that a rear facing scoop, like a cowl hood, should theoretically have almost the exact same performance gains as in a forward facing scoop?
10-27-2004, 12:00 AM
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A cowl or rear hood scoop works in a slightly different way. When you have a "wall" upon which air is interacting, high pressure area is created. So when air moving over the car and over the hood reaches the windshield (a wall) a high pressure area is created. This high pressure area forces air into the cowl of the hood.
10-27-2004, 12:55 AM
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Interesting fact about the ramjet engine design... As far as I know it hasn't been widely used. The one application that comes to mind is the SR-71A and SR-71B "Blackbird" aircraft taht travelled at speeds in excess Mach 3 
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10-27-2004, 01:22 AM
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Originally posted by 305q_ta86
... so does this also mean that a rear facing scoop, like a cowl hood, should theoretically have almost the exact same performance gains as in a forward facing scoop?
... so does this also mean that a rear facing scoop, like a cowl hood, should theoretically have almost the exact same performance gains as in a forward facing scoop?
Cowl induction is MUCH better for making power than Ram Air is. Much better.
BTW - Its called 'cowl induction' because it takes air from the base of the windshield - AKA - the cowl.
10-27-2004, 01:37 AM
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Originally posted by 305q_ta86
Long as the scoop is larger than that, it does compress, er, right?
Long as the scoop is larger than that, it does compress, er, right?
10-27-2004, 08:42 AM
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yeah, but I only had a chance to skim it because it was late and I had to do homework. 
I was thinking more of the effect the air has on your hand when you go100 mph and stick it out the window, and I thought that would be enough to compress the air. But I guess although it does, the effect is negligable.
I like the cowl setup, and I even have the air cleaner for it, but I like my THERMAC up here in canada.
I was thinking more of the effect the air has on your hand when you go100 mph and stick it out the window, and I thought that would be enough to compress the air. But I guess although it does, the effect is negligable.
I like the cowl setup, and I even have the air cleaner for it, but I like my THERMAC up here in canada.
10-27-2004, 09:36 AM
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Originally posted by 305q_ta86
I was thinking more of the effect the air has on your hand when you go100 mph and stick it out the window, and I thought that would be enough to compress the air. But I guess although it does, the effect is negligable.
I was thinking more of the effect the air has on your hand when you go100 mph and stick it out the window, and I thought that would be enough to compress the air. But I guess although it does, the effect is negligable.
Why is this incorrect? There are two types of pressure: static and dynamic. Placing of one’s hand in front of a fan, or out of a moving car’s window, clearly exerts a force on the hand as the air diverts its path to flow around it. Most people would say “See? This is a clear indication that ram air works. Clearly there is pressure from the velocity of the air.” Well, this is correct, but only to a point. This is an example of dynamic pressure, or the force any moving fluid exerts upon obstacles in its path as the gas is diverted around the obstacle.
What an engine needs is static pressure. This is the pressure the same fluid exerts on any vessel containing it at rest. For those who were physics/chemistry geeks, it is the pressure caused by the force of the molecules bouncing off of the walls of the container. The key to understanding the difference between static and dynamic pressure lies in the velocity of the gas. Dynamic pressure is only a momentum effect due to the bulk motion of the fluid around an obstacle. Static pressure is an intrinsic property of a gas or fluid just because the molecules of the fluid are moving around. Any fluid which is moving can have BOTH dynamic and static pressure, but a fluid at rest only has static pressure.
What an engine needs is static pressure. This is the pressure the same fluid exerts on any vessel containing it at rest. For those who were physics/chemistry geeks, it is the pressure caused by the force of the molecules bouncing off of the walls of the container. The key to understanding the difference between static and dynamic pressure lies in the velocity of the gas. Dynamic pressure is only a momentum effect due to the bulk motion of the fluid around an obstacle. Static pressure is an intrinsic property of a gas or fluid just because the molecules of the fluid are moving around. Any fluid which is moving can have BOTH dynamic and static pressure, but a fluid at rest only has static pressure.
10-27-2004, 10:12 AM
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Hmmm... Yeah but Ram Air sounds so cool. Adds 18 horse to my ride... but then again the chrome valve covers added 12 due to the thermal heat reflection compression dynamic process... Wait i better start a new thread about that topic.
:lala:
:lala:
10-27-2004, 10:33 AM
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That's nothing --- the "Fear This" stickers add 22 HP each, so I'm thinking about adding 3 of them to mine. Can't add more that that or I might blown out my 10-bolt or T-5 ....
10-27-2004, 10:43 AM
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Fear This" stickers add 22 HP each, so I'm thinking about adding 3 of them to mine
Last edited by Scottlb9; 10-29-2004 at 04:32 PM.
10-27-2004, 10:43 AM
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wow there are some really varied opinions on this subject in here.
Let me try to shed some light on ram air systems and related induction systems.
If you are traveling at some speed through the air you are traveling at a MACH number given as your speed over the speed of sound. the speed of sound depends on alot of things namely temperature. Anyway if you find what your mach number is when you are traveling you can also find the stagnation pressure that the air could exist at if you took the air going past your car and stopped it relative to the car. this stagnation pressure is the IDEAL pressure that could be recovered from the free stream. If the proccess by which you slow the air down to the car is not ideal then there you will get less than the stagnation pressure.
Now if we consider what mach numbers cars generally travel at (75mph is around .1 mach at sea level 59F) the stagnation pressure is roughly 1.007 (100.7%) of the free stream pressure. not much... If we go really fast (150mph or .2mach) the stagnation pressure rises to 1.028 (102.8%) of free stream pressure. keep in mind these are for perfect recovery (no losses due to recovering this pressure) which isnt really hard to do below .3 mach. So if you go 150MPH you might be able to get 2.8% more pressure to your engine, what does that mean to power -- well thats a complicated matter that I would leave to the guys who do superchargers cause they prolly know better than I how the trend goes between inlet tract pressure and power.
All these numbers are based on MIL-E-5007D standard atmosphere recovery (1962 data).
Let me try to shed some light on ram air systems and related induction systems.
If you are traveling at some speed through the air you are traveling at a MACH number given as your speed over the speed of sound. the speed of sound depends on alot of things namely temperature. Anyway if you find what your mach number is when you are traveling you can also find the stagnation pressure that the air could exist at if you took the air going past your car and stopped it relative to the car. this stagnation pressure is the IDEAL pressure that could be recovered from the free stream. If the proccess by which you slow the air down to the car is not ideal then there you will get less than the stagnation pressure.
Now if we consider what mach numbers cars generally travel at (75mph is around .1 mach at sea level 59F) the stagnation pressure is roughly 1.007 (100.7%) of the free stream pressure. not much... If we go really fast (150mph or .2mach) the stagnation pressure rises to 1.028 (102.8%) of free stream pressure. keep in mind these are for perfect recovery (no losses due to recovering this pressure) which isnt really hard to do below .3 mach. So if you go 150MPH you might be able to get 2.8% more pressure to your engine, what does that mean to power -- well thats a complicated matter that I would leave to the guys who do superchargers cause they prolly know better than I how the trend goes between inlet tract pressure and power.
All these numbers are based on MIL-E-5007D standard atmosphere recovery (1962 data).
10-27-2004, 11:02 AM
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I know for a fact that the "ram air" device that I installed on my '87 MAF car picked up 3 mph in the 1/4 mile. This HP pickup is not seen on a chassis dyno.
Providing a cold air pickup in a high pressure area will provide more cool air to the intake manifold. If the ram air pickup is located in a high pressure area, then the potential for providing more air is increased.
Maybe the "ram air" thing should simply be called "cold air induction". Or something else.
Providing a cold air pickup in a high pressure area will provide more cool air to the intake manifold. If the ram air pickup is located in a high pressure area, then the potential for providing more air is increased.
Maybe the "ram air" thing should simply be called "cold air induction". Or something else.
10-27-2004, 11:12 AM
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Excellent, its nice to see some empirical data about this. Now i wish i would have paid better attention in fluids. I actually took it from the guy that wrote the book( D. Elger), he was a horrible teacher.
Assuming no losses and air is an ideal gas, an increase in inlet pressure (mass) is directly proportional to an increase in power (PV=nRT). So if you had a 2.8% increase 1.028*14.7psi=15.11psi. If your making 300hp at atmospheric pressure (14.7psi) you will now be making 1.028*300=308.4 hp. This again is assuming no losses and under ideal conditions.
Assuming no losses and air is an ideal gas, an increase in inlet pressure (mass) is directly proportional to an increase in power (PV=nRT). So if you had a 2.8% increase 1.028*14.7psi=15.11psi. If your making 300hp at atmospheric pressure (14.7psi) you will now be making 1.028*300=308.4 hp. This again is assuming no losses and under ideal conditions.
Last edited by ME Leigh; 10-27-2004 at 11:14 AM.
10-27-2004, 11:45 AM
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IMO the base of the windshield was picked because it is a low pressure area.
Please explain the effort that goes into the hood scoops on pro-stock racecars which are normally aspirated, or for that matter an Indy or F1 car that is also normally aspirated.
I'm not an engineer, (not even close, not even a degree) but I (we) did a lot of practical work on aero by doing things like driving around at 120mph with thread hanging off misc appendages of the vehicle, even building a make shift wind tunnel and hooking the vehicle to a scale to try to measure the effect. At one time I wrote a small article for a kart racing magazine (125mph with 14horsepower, at Daytona) and built several bodies for these cars. It was all very interesting to me but w/o the educational aspects It made it a long road.
Please explain the effort that goes into the hood scoops on pro-stock racecars which are normally aspirated, or for that matter an Indy or F1 car that is also normally aspirated.
I'm not an engineer, (not even close, not even a degree) but I (we) did a lot of practical work on aero by doing things like driving around at 120mph with thread hanging off misc appendages of the vehicle, even building a make shift wind tunnel and hooking the vehicle to a scale to try to measure the effect. At one time I wrote a small article for a kart racing magazine (125mph with 14horsepower, at Daytona) and built several bodies for these cars. It was all very interesting to me but w/o the educational aspects It made it a long road.
10-27-2004, 12:38 PM
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Originally posted by blacksheep-1
IMO the base of the windshield was picked because it is a low pressure area.
IMO the base of the windshield was picked because it is a low pressure area.
10-27-2004, 12:50 PM
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The SR-71 was not a ramjet. It was a turbojet just like the all the others out there with afterburner. Turbojets, however, increase thrust with increased air speed.
The bottom of the windshield cowl is a high pressure area. They pick up the heater/AC/vent at that point because the higher pressure will drive air through the passenger compartments. The pressure increase may be minor, but it is real. The effect is more towards flow improvement than it is density increase, but it is real.
The air pressure at the 5800' altitude here is typically around 12.0 psia or less (as I type this, it's 11.777 psia). Sea level (STP) is 14.7 psia. The NHRA index for MPH is 1.0773, but the ratio of sea level to Bandimere air pressure is more like 1.22. Therefore, pressure increase and HP increase are not linear.
On the '57, when I went from open element to "cool air inlet", using the heater/vent ducts built into the fenders and fed from openings above the headlights, I showed a consistent 0.05 improvement in ET in back-to-back runs switching back and forth between the two. Guess where the biggest incremental improvement showed up - in 60' times. MPH stayed the same, indicating HP due to "ram air" was neglible, but the cool outside air vs. engine compartment air difference was significant. 57's are known for engine compartment air pressure build-up, however (showed up in the old mechanical fuel injection gage-type fuel pressure regulator problems - Smokey Yunick "solved" it by drilling big holes in the firewall and dash to let air out of the engine compartment).
The bottom of the windshield cowl is a high pressure area. They pick up the heater/AC/vent at that point because the higher pressure will drive air through the passenger compartments. The pressure increase may be minor, but it is real. The effect is more towards flow improvement than it is density increase, but it is real.
The air pressure at the 5800' altitude here is typically around 12.0 psia or less (as I type this, it's 11.777 psia). Sea level (STP) is 14.7 psia. The NHRA index for MPH is 1.0773, but the ratio of sea level to Bandimere air pressure is more like 1.22. Therefore, pressure increase and HP increase are not linear.
On the '57, when I went from open element to "cool air inlet", using the heater/vent ducts built into the fenders and fed from openings above the headlights, I showed a consistent 0.05 improvement in ET in back-to-back runs switching back and forth between the two. Guess where the biggest incremental improvement showed up - in 60' times. MPH stayed the same, indicating HP due to "ram air" was neglible, but the cool outside air vs. engine compartment air difference was significant. 57's are known for engine compartment air pressure build-up, however (showed up in the old mechanical fuel injection gage-type fuel pressure regulator problems - Smokey Yunick "solved" it by drilling big holes in the firewall and dash to let air out of the engine compartment).
10-27-2004, 12:53 PM
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The only low pressure area is behind the car. That is why it is a good idea to have the exhaust exit in the rear, it will help scavenge the exhaust gases. How much it really matters, is probably nill, but it can't hurt
10-27-2004, 01:19 PM
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I see your point. Now that I have had a chance to read it through lol.
I was thinking more of how a turbo is sort of like a small fan, and instead of having the fan on the inside of the car, place it on the outside. now, instead of moving the air past the car move the car past the air, and you get a similar effect, but I guess not. Not even close, like maybe an inmeasurable ammount less vacuum but that's it.
Well, my mind is made up. cowl hood for me.
I was thinking more of how a turbo is sort of like a small fan, and instead of having the fan on the inside of the car, place it on the outside. now, instead of moving the air past the car move the car past the air, and you get a similar effect, but I guess not. Not even close, like maybe an inmeasurable ammount less vacuum but that's it.
Well, my mind is made up. cowl hood for me.
10-27-2004, 01:52 PM
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yeah the sr-71 was a turbojet but it had a wierd feature that made it like a hybrid turbojet ramjet. it had big bleed tubes that went from the mid compressor stages directly to the afterburner. these bleeds open at high mach and the airflow through the engine increases. really cool design but you are correct -- not a pure ramjet.
10-27-2004, 02:19 PM
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yeap, its both.. kinda.
heres a good website i googled just so i wouldnt have to fumble thru explaining it
http://www.aerospaceweb.org/question...on/q0175.shtml
its both.
heres a good website i googled just so i wouldnt have to fumble thru explaining it
http://www.aerospaceweb.org/question...on/q0175.shtml
its both.
10-27-2004, 02:40 PM
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HHmmmm.. I was under the impression that the rear facing hood pulled from the boundary layer of air. True, it was not "ram air" but it was relatively undisturbed air.
10-27-2004, 03:04 PM
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The SR-71 was a major hybrid engine. It was a hybrid between a turbojet and a Scramjet, so that it would be somewhat useful at all speeds.
10-27-2004, 03:07 PM
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Originally posted by blacksheep-1
HHmmmm.. I was under the impression that the rear facing hood pulled from the boundary layer of air. True, it was not "ram air" but it was relatively undisturbed air.
HHmmmm.. I was under the impression that the rear facing hood pulled from the boundary layer of air. True, it was not "ram air" but it was relatively undisturbed air.
10-27-2004, 03:12 PM
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Yeah I'm reading something here calling the engines "turbo-ramjets"...Pratt & Whitney J58 to be exact...each delivering 32,500lb.-thrust with the afterburners! Propels this thing to over 2500mph..
Anyways, couldn't you just use a MAP sensor to get the bottom line on ram air? See how much the MAP values change when using normal induction vs. ram air induction.
Anyways, couldn't you just use a MAP sensor to get the bottom line on ram air? See how much the MAP values change when using normal induction vs. ram air induction.
10-27-2004, 03:22 PM
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Air can not be pulled, it only flows when there is a pressure or energy difference.
MAP sensors should help dispel the faux data. All you need to do is control all of the ambient conditions.
Guess I should have known better than to open my mouth about the SR-71 when I wasn't up on all the details. Having seen many of them go from the taxiway to the wild blue yonder isn't necessairly qualification as an "expert".
Horribly expensive plane to keep in the air (one expense being cleaning up the dripped fuel from the staging area after it finally took off). Only thing more expensive is loss of freedom.
10-27-2004, 03:25 PM
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Originally posted by five7kid
Guess I should have known better than to open my mouth about the SR-71 when I wasn't up on all the details. Having seen many of them go from the taxiway to the wild blue yonder isn't necessairly qualification as an "expert".
Horribly expensive plane to keep in the air (one expense being cleaning up the dripped fuel from the staging area after it finally took off). Only thing more expensive is loss of freedom.
Guess I should have known better than to open my mouth about the SR-71 when I wasn't up on all the details. Having seen many of them go from the taxiway to the wild blue yonder isn't necessairly qualification as an "expert".
Horribly expensive plane to keep in the air (one expense being cleaning up the dripped fuel from the staging area after it finally took off). Only thing more expensive is loss of freedom.
In any case, is anyone able to run the MAP sensor test? I won't have a MAP sensor for a few months more yet
10-27-2004, 03:28 PM
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Originally posted by ME Leigh
The SR-71 was a major hybrid engine. It was a hybrid between a turbojet and a Scramjet, so that it would be somewhat useful at all speeds.
The SR-71 was a major hybrid engine. It was a hybrid between a turbojet and a Scramjet, so that it would be somewhat useful at all speeds.
Heres a link (barebones but you get the point)http://www.aviation-history.com/engines/ramjet.htm
Last edited by cali92RS; 10-27-2004 at 03:31 PM.
10-27-2004, 03:29 PM
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Originally posted by five7kid
(one expense being cleaning up the dripped fuel from the staging area after it finally took off).
(one expense being cleaning up the dripped fuel from the staging area after it finally took off).
but I'm sure you already knew that.
10-27-2004, 03:36 PM
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They let them leak fuel on the ground because the skin expansion due to heating during supersonic flight sealed up the leaks. If they built it to not leak on the ground, it would buckle in flight.
(For the record, I wasn't a pilot. But, I was stationed on Okinawa and was able to get onto Kadena when I 'knew' they would be taking off and could watch them. Since I worked a rotating shift, I was often off duty at that time. Funny, I never saw one land...)
(For the record, I wasn't a pilot. But, I was stationed on Okinawa and was able to get onto Kadena when I 'knew' they would be taking off and could watch them. Since I worked a rotating shift, I was often off duty at that time. Funny, I never saw one land...)
10-27-2004, 08:25 PM
#41
yes, ram air works
I have books on how and why it works , the cowl induction was already hit dead nuts on
but, I see I will have to unpack my books in a few days so I can inform you on the facts. one thing that has already been stated is it gives little effect but, does work. (this is true) I can give the specific details latter.
I have books on how and why it works , the cowl induction was already hit dead nuts onbut, I see I will have to unpack my books in a few days so I can inform you on the facts. one thing that has already been stated is it gives little effect but, does work. (this is true) I can give the specific details latter.
10-27-2004, 10:30 PM
#42
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The real beneifit of a good ram air setup on a car is to ensure that the carb actually see's the full *ambient air pressure and temp*. (eliminating "negative boost")
On some cars the under hood air pressure as seen by the carb at speed is *less than ambient*, causing a net negative boost" A good ram air set up will eliminate this and see a modest gain in actual power, as compared to a non ram air set up on the same car.
Not all cars need it.
Just another aid in closing the gap between "Gross power" as seen on a dyno and "net as installed power" as seen in the real word.
On some cars the under hood air pressure as seen by the carb at speed is *less than ambient*, causing a net negative boost" A good ram air set up will eliminate this and see a modest gain in actual power, as compared to a non ram air set up on the same car.
Not all cars need it.
Just another aid in closing the gap between "Gross power" as seen on a dyno and "net as installed power" as seen in the real word.
10-28-2004, 10:35 PM
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.........Fast moving air creates LOW pressure. On a cowl hood the air moving over the hood where it meets the windshield creates terbulance. ( did I spell that right? ) The air spins in this area creating low pressure. High pressure air forces the spinning air into the cowl. Example, an airplane wing has a longer surface on the top, slightly rounded, than on the bottom. The air has to move quicker over the top to meet the air on the bottom as the wing slices through the air. This cause a low pressure over the wing and high pressure under the wing. Thats what holds the plane in the air. Or if you meet a truck on the highway you seem to be sucked in toward the truck. The air between you and the truck is a low pressure and the outside air is a high pressure and pushes you toward the truck........Zapr.
10-28-2004, 10:39 PM
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Well-stated. I have no opinion on the matter right now because if I think about this at all, the girlfriend on the other end of the phone right now wouldn't be too happy I'm not listening 
10-28-2004, 10:50 PM
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Originally posted by zapr
.........Fast moving air creates LOW pressure. On a cowl hood the air moving over the hood where it meets the windshield creates terbulance. ( did I spell that right? ) The air spins in this area creating low pressure. High pressure air forces the spinning air into the cowl. Example, an airplane wing has a longer surface on the top, slightly rounded, than on the bottom. The air has to move quicker over the top to meet the air on the bottom as the wing slices through the air. This cause a low pressure over the wing and high pressure under the wing. Thats what holds the plane in the air. Or if you meet a truck on the highway you seem to be sucked in toward the truck. The air between you and the truck is a low pressure and the outside air is a high pressure and pushes you toward the truck........Zapr.
.........Fast moving air creates LOW pressure. On a cowl hood the air moving over the hood where it meets the windshield creates terbulance. ( did I spell that right? ) The air spins in this area creating low pressure. High pressure air forces the spinning air into the cowl. Example, an airplane wing has a longer surface on the top, slightly rounded, than on the bottom. The air has to move quicker over the top to meet the air on the bottom as the wing slices through the air. This cause a low pressure over the wing and high pressure under the wing. Thats what holds the plane in the air. Or if you meet a truck on the highway you seem to be sucked in toward the truck. The air between you and the truck is a low pressure and the outside air is a high pressure and pushes you toward the truck........Zapr.
10-28-2004, 11:14 PM
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Actually...its hard to debate.
There is two ways this can be looked upon...
1)Because of how the cowl is designed, I would also assume the air is low pressure. However, this wouldn't help engine performance at all. In fact it'd make it worse.
With that said, everything stated by zapr is true and logical thinking. Its like exhaust flow scavenging and how some people believe that having the exhaust tips in the rear of the car help to scavenge the exhaust because of the low pressure created behind the car. There is a low pressure zone created behind the cowl as the air rushes over the cowl, the air in the cowl would seem to want to flow out to the lower pressure zone.
HOWEVER
2)With the low pressure zone created right behind the cowl, air around this low pressure zone is going to want to move into this low pressure area. The air from inside the cowl would want to, but the pressures in the engine are even lower so the air in the cowl is still being pulled into the engine. This leaves the air in the high-pressure zone at the base of the windshield to rush in and fill the low-pressure zone and continue into the cowl and into the motor.
Again, this can be argued because the car is moving forward, why would the air want to rush forward into the cowl, even if there is a pressure difference.
With all that being said, I suppose #2 would be correct because it is clear that cowl induction does give some sort of an advantage besides just cold air.
There is two ways this can be looked upon...
1)Because of how the cowl is designed, I would also assume the air is low pressure. However, this wouldn't help engine performance at all. In fact it'd make it worse.
With that said, everything stated by zapr is true and logical thinking. Its like exhaust flow scavenging and how some people believe that having the exhaust tips in the rear of the car help to scavenge the exhaust because of the low pressure created behind the car. There is a low pressure zone created behind the cowl as the air rushes over the cowl, the air in the cowl would seem to want to flow out to the lower pressure zone.
HOWEVER
2)With the low pressure zone created right behind the cowl, air around this low pressure zone is going to want to move into this low pressure area. The air from inside the cowl would want to, but the pressures in the engine are even lower so the air in the cowl is still being pulled into the engine. This leaves the air in the high-pressure zone at the base of the windshield to rush in and fill the low-pressure zone and continue into the cowl and into the motor.
Again, this can be argued because the car is moving forward, why would the air want to rush forward into the cowl, even if there is a pressure difference.
With all that being said, I suppose #2 would be correct because it is clear that cowl induction does give some sort of an advantage besides just cold air.
10-29-2004, 12:46 AM
#47
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Car: 2000 firehawk
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theres no way to debate it, argue it, or even slice it for that matter. if the teacher here could answer one fairly common sense question, don't ya think at somepoint over the last 35 + some years that someone would have catched on that "Ram Air"
does nothing and sued pontiac??? Or would these cars of ours have made it today to be the legend they are? or your saying were all suckas for paying the few xtra bux for it?
does nothing and sued pontiac??? Or would these cars of ours have made it today to be the legend they are? or your saying were all suckas for paying the few xtra bux for it?
10-29-2004, 12:55 AM
#48
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Car: 92 Form, 91 Z28, 89 GTA, 86 Z28
Engine: 5.7 TPI, LG4
Transmission: 700R4, 700R4
Axle/Gears: 3.27, 2.73
This weekend, Sunday perhaps, I'll do the MAP sensor tests for everyone to see. I have my car running on 2 ECU's with either one controlling injection and/or spark and/or IAC. I can run entirely on stock, which is MAF, and use my other ECU to read MAP (I work for a fuel injection company - Injection Logic if you care). I can run a tube from the MAP to any point around the car, and compare it against a Baro reading of the MAP at key on, or slow speed. I'll even try a small tin cup screwed to the front license with the tip of the MAP tube in it, and also, some cowl measurements, and maybe some under hood measurements.
My two bits: Ram air may help air cross an air filter easier, and it is calculated using the stagnation pressure combined with the velocity of the air entering the intake, and it's usually from a colder region.
If you calculate the stagnation pressure, I get about .45 kPa available at about 60 mph, and 1.5 kPa at about 110 mph. Hardly enough to "boost" a manifold with an engine sucking behind it, but it will help air cross the filter and help with breathing.
My two bits: Ram air may help air cross an air filter easier, and it is calculated using the stagnation pressure combined with the velocity of the air entering the intake, and it's usually from a colder region.
If you calculate the stagnation pressure, I get about .45 kPa available at about 60 mph, and 1.5 kPa at about 110 mph. Hardly enough to "boost" a manifold with an engine sucking behind it, but it will help air cross the filter and help with breathing.
10-29-2004, 07:45 AM
#49
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I'm not convinced that Pontiac's Ram Air has any affect on any of their cars. Sure the WS6 and SS are rated a few HP more than the Z28/TA. Have you seen the exhaust manifolds on the WS6/SS cars? My buddy has a 6spd '99 SS and his dad has an auto '02 Z28 vert, and the SS has some mini-headers on it from the factory, whereas the Z28 has some standard exhaust manifolds. This is where these cars get the extra power from, I don't think the ram air really does anything for them.
However, I can see your point about getting air across the filter better as long as the system is well-designed.
However, I can see your point about getting air across the filter better as long as the system is well-designed.
10-29-2004, 08:23 AM
#50
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Car: 2016 Ram 1500
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The cowl induction problem is solved as such:
The streamlines of air going over the hood are turned upwards when they meet the windshield. This turning causes some of the dynamic pressure to be recovered on the surface that is turning the flow. Not stagnating the flow by any means but if you got an old truck like I do the windshield is nearly vertical and virtually all of the stagnation pressure is recovered against the windshield.
The streamlines of air going over the hood are turned upwards when they meet the windshield. This turning causes some of the dynamic pressure to be recovered on the surface that is turning the flow. Not stagnating the flow by any means but if you got an old truck like I do the windshield is nearly vertical and virtually all of the stagnation pressure is recovered against the windshield.