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I know ram air induction is a CFM thing but does turbulent air flow effect overall performance?

I'm trying to make sense of the study that was posted on the link you provided.

I've also noticed the J's Racing air duct that few people sport. I have never seen the whole thing for it besides the outer duct piece itself. Is there more to it than what you see outside? The inlet for the air seems rather small. Also, is there a significant amount of air flow come in the air duct? I know when driving, the air flow follows the surface of the car but I'm having a hard time seeing it just follow into the air duct. It would be better to have the air duct protrude out and force the air in. If the air duct were to follow the contours of the surface, optimum airflow to the intake isn't achieved.

Being that air flows with the contour of the surface, brakes ducts are useful in cooling the brakes since they protrude from the contour of the surface and direct the air flow where needed. Proven on race built cars.
 

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Good Info! REP
 

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Ugliest ram air ducts I've ever seen are on the MR2's ... ugh.. I love that car, but I hate those ducts.
 

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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.
 

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ram air myth cont.

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.
I found this over on H-T and figure it'd be some extra food for thought on this topic.
 
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Just so that the dynamic of this can be understood
It's not just the air velocity being increased into a venturi,
AND the intake stroke being met with X level of atmosphere
BUT the level of atmosphere being held stable with the
valve opening / vacuum event. This SINGLE even
with out a "ram" system can only draw X amount of
volume of air into the chamber, basic physics solve the volume
via cfm & duration of the valve opening event.
So with that understood let read with Patrick Ledford
has to say next (and don't forget he's a president and not a engineer)

http://www.vararam.com/technical01.html

Next lets take NASA's engineers Q&A

http://www-psao.grc.nasa.gov/asao.quiz/september.98.html

OK so where does this leave us ?

IF it does bring a colder charge into the motor it's good , but it will most likely
NOT give you Bigpowah because there is a ram.
IF it helps smooth the airflow into the inlet tract it's good, but most likely
it will increase turbulence and decrease recover time for the valve opening event, but we don't drive jets ;)

I've spent many hours testing cai/sri on cars from datsuns/rx7/honda and the best has always been about 1.give the intake event recovery time 2. do this smoothly 3. bring the coldest air into the tract

Hope this helps
 
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I would gather that what one does by building a 'ram-air' duct is not pressurizing the air over that of the atmosphere, rather that it would reduce the vacuum of the intake tract.... reducing pumping losses.



Now, at freeway speed a car with a resonator or even a conceled cold air intake would have an obvious restriction to outside air by being contained inside the bumper/wheelwell correct? However the same car with a bumper duct that feeds the stock airbox/cold air intake would have nothing between filter and outside air ergo reduced restriction, right?

If this air is pressurized against the front of the car as drag, then said duct would provide an easier route for engine charge air to enter....so if the charge is easier to ingest into the intake tract then, the suction action of intake stroke would require less effort.

Ic, if you have the time and means to do so I would suggest you install a vacuum gauge in front of the throttle plate. The engine running at closed throttle would provide a small amount if any measured vacuum, when at WOT I think there would be considerable vacuum in the intake pipe. With your ducting installed I bet this vacuum would be lower at 80mph.

Not ram-air but maybe just a better access to outside air.

If we are driving into a headwind we aren't losing horsepower, merely using more work for the same job. Driving with a tailwind we again aren't gaining horsepower, but we are definitely using less work for the same job!

Kinda like a lightened flywheel does not create horsepower but it does allow the engine to direct more energy to the forward movement of the car via the gearbox instead of storing it in the flywheel.
 

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Discussion Starter #14 (Edited)
bspeed said:
Kinda like a lightened flywheel does not create horsepower but it does allow the engine to direct more energy to the forward movement of the car via the gearbox instead of storing it in the flywheel.
I think this is an excellent analogy.

Thinking of a cold air intake (which is usually located between the bumper and the passenger front wheel, on a Honda at least,) I see it quite possible that the air passing around the outside of the bumper and the wheel could create slightly negative pressure around the filter/intake tract. This is obviously no good if the vacuum created by the receeding pistons have to first overcome an ambient vacuum before drawing in a charge. So in a ram air setup, no extra boost is created, but if there is not significant turbulence, then you recieve an unhindered cold charge.

Also, I'm no expert, but the 'reverse' hood scoops, where the opening is directly in front of the windshield, works to some effect as well. This is because the air directly above the body panels of the car are more or less stagnant. However, the air coming over the hood hits the windshield and partially deflects back down towards the hood. The scoop is then designed to take advantage of this flow and catches the air on it's way back down. This, I would think would have to apparently be true, because the other option of a reverse facing scoop would be a vacuum at the opening, which would be BAD for breathing. For instance, my moms '82 TransAm has a reverse scoop where the opening directly at the base of the windshield and is fed directly into the sealed air filter atop the carburator. Alternatively, reverse scoops located further forward on the hood are not plumbed directly into the intake and are designed to COOL the engine bay via the suction created at the mouth of the vent as I mentioned above.

Anyhow, I like ram air and Dave Rodabaugh can lick my ass.

-ic
 
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icarusdown said:
Anyhow, I like ram air and Dave Rodabaugh can lick my ass.

-ic
Yeah fcuk that assclown. Ram air may only work in our minds, but we kick ass so it is still cool!
 

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I think "Ram air" has nothing to do with compressing air. It's all about a free supply of air thats not from a hot engine bay. When you get a chance, look at the stock air box if your civic (well, 95 Ex here). It has little ducts. From what I can assume, it is designed to offer air to the intake that is from outside. In fact, Spoon doesn't reccomend replaced the air box, they simply offer a drop in filter (last I checked).

I may be wrong, on both items, but I have read that with my car, a CAI is pointless because the airbox works just as week with a high flow filter.
 

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Haysoos said:
I think "Ram air" has nothing to do with compressing air. It's all about a free supply of air thats not from a hot engine bay.
 
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