People with knowledge of Ram-Air.......

Discussion in 'American Cars' started by bob777, Sep 4, 2004.

  1. PandaBeat posted this artical, I was wondering if there is any thruth to this....(I'm not very technical with these type of things)


    "Ram Air" Doesnt exist.
    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.


     
  2. #2 bob777, Sep 4, 2004
    Last edited by a moderator: Apr 25, 2016
  3. There was a discussion a couple years back in Tech about this, and the article is correct (or at least the part saying that ram air is a myth- I only scanned it). I believe someone was even saying that "cowl" type hoods are better for getting more air into the engine bay. It's been a while, though, so I'm not sure about that.
    But, yes. The article is correct.
     
  4. I don't understand how the engine would take in air from the engine bay, doesn't the engien take in air through the air intake or ram-air system?
     
  5. Honestly, I wish I could provide the actual proof that I saw back in Tech, but I'm not a physics buff, so I can't. Any answer I give you will just be some BS. You should've posted this in Tech, or tell one of the mods to move it. You'll probably get a good answer there.
     
  6. cowl induction gets cold air the same as a forward facing scoop
    with less wind resistance

    you can't compress air in an open enviroment
    once the intake trac is full of air, the rest just goes the path of least resistance
     
  7. It has nothing to do with pressure however. It has to do with the ease at which the air gets drawn in. the intake is in a constant vacuum or draw. As such, the intake is drawing in air at the intake nozzle. With a ram air, it does nothing more than supply a steady source of air from which to draw without resistance. Cowl does the same thing but instead the pressure of the windshield front does it instead.

    Want to experiment, blow on the end of a running vaccuum and feel how it sucks the air in. If there is air traveling in the direction of the vacuum, it doesn't have to work as hard. The more direct the air source, the less work. That is why the WS6 has more power than the SS because it is more direct.

    Pressure isnt what allows ram air to work, it is the ease at which it can draw in air.
     
  8. Doesnt the 575 Maranello use ram air?
     
  9. Some air must go in but its no great system. Its is more useful than a normal hood. But cowl is better.
     
  10. boredup32, monkey, me and a few other members discussed this to a great degree(Was like 15 pages or somethin) about a year and a half ago and yes, ram air is not effective and the drag created tends to overcome the minute hp advantages(at 150mph or something there was a .3 percent gain for example). the gains we DO see is from the cold air, not the "higher velocity air".
     
  11. Can someone please explain how a Cowl Hood works? I'm not understanding.
     
  12. The cowl induction on a 1970 chevelle ss 396 or an ss 454 works from the following manner.It is hood with a small mobile hatch which function is to give air to the engine through the air filter which goes directly to the carb then mixes itsself to gas which gives a highly powreful mix in order to give better acceleration. That is what i read from an old road and track magazine of year 1970.
    The 1968-1970 pontiac GTOs used the ram air III and IV engines.The 1968-1970 Oldsmobile 442 used the force air induction system.1968-1970 Dodge and Plymouth used ramcharger scoop.Other type of ram air systems were the shaker scoops available on 1970-71 barracudas an challys as well las on the 1968-1970 ford mustang mach1 mostly cobra jets.
    These systems are slightly difrent in te aspect as compared to the cowl induction chevy system but their function is the same.
     
  13. So basicaly, Ram-Air, Air Intakes, and Cowl induction all do the same thing, so is there any one that has an advantage over another?
     
  14. I heard a scoop that sucks in air for the engine is only effective at 200 MPH+.
     
  15. No.It is just different systems which has the function.The fastest stock car with a shaker (also a ram air system) was the 1970 plymouth hemi cuda 12.92sec @ 110mph.
    Then followed the 1968 huts olds of 1968 13.15 @ 109mph, the 1970 buick gs 455 stage 1 13.38 @ 109mph, the chevelle ss 454 ls6 13.70 @ 108mph
    All this on bias tires.
     
  16. If you look at all the cars that have Ram-air, the engine takes it's air from the top of the hood and the closer to the front of the car, the better. The whole idea is that the cooler air to go in the intake and mix it with gasoline. Cooler air makes a better explosion in the combustion chamber.

    Today's cars takes the air lower in the engine bay and gets warmed up by the engine. And that's the idea behind Ran-Air, to take cooler air for the engine.
     
  17. I'm taking fluid dynamics now. I'll have to figure the numbers out for myself when I get through.
     
  18. One of the engineers who is a member on my f-body board went through a lengthy explanation of how the Ram Air on the f-bodies is good for 3 extra HP at 100 mph.

    Ram Air is a gimmick, Draper. That's really all you have to know.
     
  19. i saw on tv that the huyabusa's ram air ads like 10hp at 180mph.
     
  20. but on Ferraris its good for 15+hp, hardly a gimmick.
     
  21. that last GTO/monaro looks #$%#ing awesome, post it again.
     
  22. BullSH!T ram Air does work, on particlar cars maybe not because of where the air cleaner is located, But the whole poiint is to allow air to flow more easily! It has to help in that, If It doesnt then why would they put it? Its not like a R!cer FWd with a wing, The factory puts them stock on WS6s and other old GTOs as well as many other cars like the 71 Mustang Mach1 and others, ANd Cowl Induction on Chevys Work as well as Air Grabber on the Mopars

    I am not providin solid proof that Ram AIr does wrok, But still U dont have to 100% do reasearch on everything, Use ure brain sometimes..... I am 99% sure that Ram Air helps with at least something! MAybe It wont Ram or compress the Air like a supercharger(obvioulsy) but has to increase air flow somehow
     
  23. Shouldn't a large ram air that goes directly around the air cleaner actually do more for performance. Meaning that it would only be getting outside air, outside air is cooler and more dense so it would carry more oxygen.
     
  24. Thats what Im saying, Give a reasonable explanation IF it doesnt work and still I will be skeptikal, MAybe they are saying it doesnt really "RAM" air like the name, I think thats what they mean, But no question about if it helps the air flow or not! It definately has to help!
     
  25. In fact ram airs systems were made to giving a better acceleration to the car tahnks the air that directly went to the aircleaner and then through the carb which made a highly powerful mix with gasoline the car had an ability to accelerate fast.
    A 1970 chevelle ss 454 ls6 with cowl induction was good from 0-60mph in 4.5sec and quarter mile in 13.70 @ 109mph.
     

Share This Page