Why RAM Air is a myth!!! Long Read (Wall of text)

[live2well]

This is not my work but is a good explanation of why RAM AIR in Autos is a myth.

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 just 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 experimentallydetermined
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 of mass, known as a stoichiometric 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 0.3 (or about 1/3 the speed of sound, 228 MPH at sea level), 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 (I.e. speeds less than Mach 0.3).
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."

I hope now we all can understand why Ram AIR is a myth.

[Camaro509]

You weren't kidding about a 'wall of text'. That's as far as I got, can you provide the Cliff's Notes version please? j/k, I read it.

Ram-air is not a myth
Ram-air is a myth concerning automobiles at <= mach .3

I'mma gonna tape some card board to my hood to test this
all out this coming weekend, will post results when all is said
and done. *goes off looking for some more duct tape...

[live2well]

Originally Posted by Camaro509

Ram-air is not a myth
Ram-air is a myth concerning automobiles at <= mach .3

exactly !!!

[DEW]

Cold air....................Now thats not a myth!

[ZombieEatsYou]

How's this from this thread?

Lot's of math

[HaveBlue]

Originally Posted by live2well

This is not my work but is a good explanation of why RAM AIR in Autos is a myth.


I hope now we all can understand why Ram AIR is a myth.

live2well, THANK YOU!!!

My post had way to much math it it. This is much better. This should be a sticky. Companies that advertise "ram air" are at best, ill-informed and at worst ,out right deceptive.

[camaro692]

Great post!

[Melson]

Very Good Post!

[1camaro70]

is this a premptive strike on vararam or other CAI manufacturers?
It is very interesting, and once vararam actually shows us some data I would like a technical discussion between them and the others that have posted on this subject.

[2SSRS@Gen5diy]

So the myth will post and prove that it makes more HP, And it's the myth.

[moto-camaro]

if you can't beat em.... confuse 'em with a wall of text!
So my car can have ram-air... i've just gotta break Mach 0.3


seriously, it'd be REALLY interesting to see a debate between the company's that manufacture these ram-air hoods, and the science people who can explain how everything works.

[1camaro70]

I don't believe that there is no ram effect, it might not follow the calculations, but if vararam does better than 15 HP, or the member who tested it and reports 40 HP, then it does not compute. Please vararam post your results and prove the myth wrong.

[2SSRS@Gen5diy]

I am the member that posted that 40 hp, And i called them today to push tem to get all the info out, And there working on all of it.

[HaveBlue]

Originally Posted by 1camaro70

is this a premptive strike on vararam or other CAI manufacturers?
It is very interesting, and once vararam actually shows us some data I would like a technical discussion between them and the others that have posted on this subject.

no CAI manufacturers here, just pointing out one of many myths perpetuated over the years by marketing. Ted Jannety just tested all the intakes and he says it's a myth too. He's said it numerous times before the tests.

Originally Posted by 2SSRS

So the myth will post and prove that it makes more HP, And it's the myth.

Getting your engine the additional air (and cooler) it wants, will make more power. It just has nothing to do ram air.

Originally Posted by moto-camaro

if you can't beat em.... confuse 'em with a wall of text!
So my car can have ram-air... i've just gotta break Mach 0.3

seriously, it'd be REALLY interesting to see a debate between the company's that manufacture these ram-air hoods, and the science people who can explain how everything works.

It's just marketing folks. It's been hyped for so long it's just considered true. Show the scientific data (you can data acquisition the crap out of anything these days) that supports ram-air effect at car speeds. Nobody is saying that a less restrictive higher flow intake doesn't make more power than stock. They do. It's just what you call it.

Anybody want to buy a 3/4 race cam?