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Old 01-31-2005, 11:00 PM   #21
Sol
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If you take the Grand Am as an example, the Ram Air on the GT model only gives a few more HP than a similar 3400 V6 without Ram Air. This is probably because it has a better way of sucking in nice cold fresh air from the outside, and having a smoother way of entering the engine.
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Old 01-31-2005, 11:01 PM   #22
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Quote:
Originally Posted by Sol
If you take the Grand Am as an example, the Ram Air on the GT model only gives a few more HP than a similar 3400 V6 without Ram Air. This is probably because it has a better way of sucking in nice cold fresh air from the outside, and having a smoother way of entering the engine.
Have you seen that one personally? It'* a joke. I checked one out at the dealer last summer. It RAMS from a little slit in the grille.
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Old 01-31-2005, 11:02 PM   #23
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Yes, my mom drives one.



There'* a good pic of it. The hood scoops are non-functional, but you can see where the air comes in.
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Old 01-31-2005, 11:14 PM   #24
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Damn, I love Pontiac styling.
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Old 02-01-2005, 01:05 AM   #25
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IN CONCLUSION:

No real pressurization of the air, despite the name.

Good at reducing temps to close to ambient air.
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Old 02-01-2005, 01:23 AM   #26
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Yes but I believe it can have a small pressurizing effect although not as much as the cooling effect.

Quote:
1) I'am going to use standard temp and press for the air

2) area of 3" pipe = pi * radius squared
3.14 * 1.5in * 1.5in = 7.07 in2

3) Inside volume of pipe = area * length
I wanted to know how long a piece of 3" pipe had to be to half an internal volume of 1 cubic foot. I rearanged the equation:
length = volume / area
length = 1 ft3/ 7.07 in2 = 1 ft3 * 144in2 / 7.07in2 = 20.4 ft

4) OK now I know that 1 ft3 is the volume of a 20.4 ft long piece of 3" pipe. I also know that Iam looking for 800 ft3/min. so this is next:
Speed of the air in the pipe (mph) = (800 * 20.4 * 60) / 5280
800 is cfm (ft3/min)
20.4 (ft of pipe for one cfm)
60 (convert from minutes to hours)
5280 (convert from feet to miles)

ANWSER: 185.45 mph!!! Air speed in a 3" pipe with 800 cfm of air moving through it. Makes me shake my head but it appears to be right. I also calculated for a 4" pipe and the speed dropped to 104 mph.



I use twin 9" x 4" scoops that Ram into twin 4" hose into a sealed air box for my Firebird.

The frontal ram area equates to 72 square inches.
That equates to a speed of around 75 mph.
I know it made a difference for me over simply just the cold air effect.....I experimented before and after, cool air vs. ram air. Small but measureable in the 1/4 mi times (.1 sec)
Calculate all you want but it works for me.

Now I know the 4" hose on my Bonne does not have any pressurizing effect. It is simply ramming cool air into the intake chamber. It works very well because I measure the same temp inside the box as outside ambient temp. When I lost the elbow a few times (blew off at over 100 mph) the temp inside the chamber rose to 10-15 F above ambient...even with the hose drawing air from the frontal area but with no ram effect.
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Old 02-01-2005, 01:29 AM   #27
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Paul, I think the only way to prove this is for the two of us to take MAF readings at different speeds, with the ram-air on and off. That'll tell us what'* really going on. You game? Of course, we gotta wait for my trans!
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Old 02-01-2005, 02:41 AM   #28
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Along with what I posted last this is all I'll say on the matter. Don't really wanna debate, I've upset enough people trying to dispel myths in the past:
(long but worth the read even if you don't believe it)
-----------------------------------------------


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’* 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’* 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’* 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’* density. As the air flows through the intake tract, it loses pressure, and as the pressure decreases, so does the air’* 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’* hand in front of a fan, or out of a moving car’* 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’* velocity (as the vehicle moves through the air) for an increase in static pressure (since static pressure is a part of a gas’* 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.
http://www.vetteguru.com/ramair/
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Old 02-01-2005, 12:37 PM   #29
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I'll buy it. I agree 100%. My point in taking MAF readings on 2 cars running it was to further prove that it does nothing for induction other than temp.
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Old 02-01-2005, 01:10 PM   #30
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In the late '60'* and early '70'* the Ram Air package on the Firebird and GTO included the hood scoops, the special air-cleaner with the addition of ports for the scoops to feed, but most importantly, the intake, cylinder heads and exhaust manifolds were reworked. The intake, exhaust and heads had larger ports and the exhaust manifolds were closer to headers than the usual restrictive setup.

So, the Ram Air package was just that. Several modifications to increase the flow of air and exhaust. Now, I remember, but haven't been able to find, ad copy which described the intake as a means to suck in cold air. No mention that the scoops added any appreciable pressure to the induction. In fact, I do recall reading about the shaker style hood scoops and seeing them described as nice when functional, but too far toward the middle of the hood to benefit from the high-pressure areas of the leading edge of the hood, or the intersection of hood to windshield.

I think Ram Air has taken on a perceived meaning apart from its intentions.
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