Do Ram Air intake systems really work?
12-05-2005, 09:33 AM
#1
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Do Ram Air intake systems really work?
What do we all think about Ram Air intake systems? Do they really provide a significant measurable benefit? I went to my old stomping grounds and pulled some quotes out for your review....many other people believe that Ram Air systems are worthless. I want to get some views from the RX-8 community on whether or not Ram Air really works... ie the racing beat ram air system.....I like the whole concept and believe Ram Air should be able to provide some benefit.
From the 300ZX forum www.twinturbo.net
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"Ram Air" is a bs marketing concept to sell Firechickens.
http://www.twinturbo.net/net/viewmsg...msg_id=1686941
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"Ram Air" >> Requires 420mph to produce 1 psi of pressure> - MikeeZ
http://www.twinturbo.net/net/viewmsg...s=ram%3a%3aair
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......Suposedly, physics experiments proved ram air is only beneficial at 80+mph.
http://www.twinturbo.net/net/viewmsg...&msg_id=126855
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"Perfect Design" (i.e. not pressure loss inside ram air ducting) will only increase pressure at intake filter by 0.17 psi at 100mph so only a 1.1% increase in air mass flow. For lower speeds, the gain decreases with the square of the velocity.
http://www.twinturbo.net/net/viewmsg...ir%3a%3asystem
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He cant afford it, all his money goes towards crack (I thought I would throw in a classic flaming response also
)
http://www.twinturbo.net/net/viewmsg.aspx?
forum=technical&msg_id=705152
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From the 300ZX forum www.twinturbo.net
-------------------------------------------------------------------------
"Ram Air" is a bs marketing concept to sell Firechickens.
http://www.twinturbo.net/net/viewmsg...msg_id=1686941
--------------------------------------------------------------------
"Ram Air" >> Requires 420mph to produce 1 psi of pressure> - MikeeZ
http://www.twinturbo.net/net/viewmsg...s=ram%3a%3aair
-------------------------------------------------------------------------
......Suposedly, physics experiments proved ram air is only beneficial at 80+mph.
http://www.twinturbo.net/net/viewmsg...&msg_id=126855
-------------------------------------------------------------------------
"Perfect Design" (i.e. not pressure loss inside ram air ducting) will only increase pressure at intake filter by 0.17 psi at 100mph so only a 1.1% increase in air mass flow. For lower speeds, the gain decreases with the square of the velocity.
http://www.twinturbo.net/net/viewmsg...ir%3a%3asystem
-----------------------------------------------------------------------
He cant afford it, all his money goes towards crack (I thought I would throw in a classic flaming response also
)http://www.twinturbo.net/net/viewmsg.aspx?
forum=technical&msg_id=705152
----------------------------------------------------------------------
12-05-2005, 09:42 AM
#2
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Here is what rotarygod has to say about ram air systems.
Once again I feel compelled to write something. This one is about the myths of ram air and the effects of intake tuning in general.
There are many ways to get air into an engine. The easiest way is to just slap a filter on it and let it suck it in by itself. This is the most common method. As we all know, the more air we get into the engine, the more fuel we can add, and the more power we can get. This is the basis for forced induction. Unfortunately forced induction requires that a little bit of power be robbed from the engine to make more. Since we still come out ahead in the long run, this is acceptable. Obviously there are some systems that are more efficient than others. The goal of everyone of them remains the same though. More air is more power.
There is more to making power than just giving the engine the required amount of air. There are also other ways to increase output. The length of the intake runners makes a huge difference in where the engine makes the most power. Shorter runners make better high rpm power. Longer runners make better low rpm power. This is because of pressure waves inside the manifold being timed to help add more air to the engine just before the ports close. In a sense this is ram air. However this is not ram air in the context that I am going to focus on right now.
In a ram air intake system, air is supposedly channeled straight from the front of the car and into the engine. This high speed air supposedly forces more of itself into your engine and gives you a gain in power. Can this actually work? Yes and no. It depends how it is done.
Most systems out on the market today are "cold air". The don't so much ram air into the engine as they do just send cold air to it. By cold air I mean air from outside that is colder than the hot engine bay air. Colder air is denser air and denser air is more air. This doesn't mean it is ram air though. Let's get a little technical for a minute.
The rotary as we all know doesn't flow the same amount of air as a 1.3 liter engine. It is closer to a 2.6 liter engine interms of size but it still flows more air than this. for everything to work properly, we have to size it's airflow at almost 4 liters. That's alot more than 1.3. Since we really want our intake air to be going no faster than 180 ft/sec. through the throttlebody we need to figure out how much flow that is at max rpm. In the case of the Renesis it is about 9500 rpm. At 9500 rpm this would be about a 3" inlet pipe. It would be close. The throttlebody on the RX-8 is a little smaller than this though. Just for argument sake, we'll stick with the 3" number.
If a we were at 9500 rpm, we would need to be moving at 180 ft/sec or about 123 mph just to make the forward velocity of the vehicle the same as the airflow into the engine. You'd have to go a whole lot faster to get any usable gain as this is only the break even spot. Obviously we would be at a lower rpm at 123 mph than this so we should have more air entering the engine through ram air right? Not necessarily. If we were to put our air filter straight into the path of the outside incoming air, we still wouldn't get a ram air effect. The 3" inlet pipe is not going to take in hardly any more air. The reason is that as air is trying to force or ram itself into this pipe, it is doing so in a very small space. Maybe a little more will get in, but you won't really notice it. Luckily there is a way to get around this.
Let's say we used a 6" diameter pipe that faced forwards into the airstream. We can't just taper this down into a 3" pipe since the added air will just reverse itself. We'd actually get less air into the engine this way since we'd have to speed the air up as it enters the pipe. when we speed the air up, we lower it's pressure. That is not the goal. Less pressure is less air. If we feed the 6" pipe into an airbox or plenum chamber, we can alleviate this problem. We then feed the 3" pipe to the engine into this. The 6" inlet pipe has 4 times the area of the 3" pipe. When we bring all of this air into the airbox, the greater area or the airbox forces the air to slow down. When we slow air down, we increase it's pressure. This may confuse you when it comes to turbochargers or superchargers but I assure you this is what is happening in them too. The exception to this is the roots blower. It doesn't compress the air by slowing it down. It speeds it up and causes it to build up in the intake manifold. This is where the pressure is increased.
Back on topic. This airbox is now pressurized to some extent. Don't expect gains of supercharger proportions though. This higher pressure air is what the 3" pipe to the engine is feeding off of. Suddenly we have higher than ambient pressure entering the engine. We call this boost! Now we are ramming air into the engine. In order to utilize ram air, we must find a collection point for the air where it can build pressure. If you just have a filter in the airstream, you don't have this.
Racing Beat found that on their 1st generation Bonneville RX-7, a true functional ram air system added 3 mph to the top speed of the car. That doesn't sound like much but at 180 mph, it takes alot of power to go a little faster. This should still emphasize the fact though that you are not going to get incredible results from ram air. It is alot of effort for a little gain. If we could get even 1 psi of extra air into the engine, on a 200 hp engine that is still around 13 hp more. This is only at high speeds but it is more than you have now. If you find old pictures of the Racing Beat 1st gen. you will notice that there is a single 6" pipe that is fed air from the front of the car. It also dumps into a large plenum chamber in front of the throttlebody.
Next time you see a product that is marketed as "ram air" ask yourself, is it really?
There are many ways to get air into an engine. The easiest way is to just slap a filter on it and let it suck it in by itself. This is the most common method. As we all know, the more air we get into the engine, the more fuel we can add, and the more power we can get. This is the basis for forced induction. Unfortunately forced induction requires that a little bit of power be robbed from the engine to make more. Since we still come out ahead in the long run, this is acceptable. Obviously there are some systems that are more efficient than others. The goal of everyone of them remains the same though. More air is more power.
There is more to making power than just giving the engine the required amount of air. There are also other ways to increase output. The length of the intake runners makes a huge difference in where the engine makes the most power. Shorter runners make better high rpm power. Longer runners make better low rpm power. This is because of pressure waves inside the manifold being timed to help add more air to the engine just before the ports close. In a sense this is ram air. However this is not ram air in the context that I am going to focus on right now.
In a ram air intake system, air is supposedly channeled straight from the front of the car and into the engine. This high speed air supposedly forces more of itself into your engine and gives you a gain in power. Can this actually work? Yes and no. It depends how it is done.
Most systems out on the market today are "cold air". The don't so much ram air into the engine as they do just send cold air to it. By cold air I mean air from outside that is colder than the hot engine bay air. Colder air is denser air and denser air is more air. This doesn't mean it is ram air though. Let's get a little technical for a minute.
The rotary as we all know doesn't flow the same amount of air as a 1.3 liter engine. It is closer to a 2.6 liter engine interms of size but it still flows more air than this. for everything to work properly, we have to size it's airflow at almost 4 liters. That's alot more than 1.3. Since we really want our intake air to be going no faster than 180 ft/sec. through the throttlebody we need to figure out how much flow that is at max rpm. In the case of the Renesis it is about 9500 rpm. At 9500 rpm this would be about a 3" inlet pipe. It would be close. The throttlebody on the RX-8 is a little smaller than this though. Just for argument sake, we'll stick with the 3" number.
If a we were at 9500 rpm, we would need to be moving at 180 ft/sec or about 123 mph just to make the forward velocity of the vehicle the same as the airflow into the engine. You'd have to go a whole lot faster to get any usable gain as this is only the break even spot. Obviously we would be at a lower rpm at 123 mph than this so we should have more air entering the engine through ram air right? Not necessarily. If we were to put our air filter straight into the path of the outside incoming air, we still wouldn't get a ram air effect. The 3" inlet pipe is not going to take in hardly any more air. The reason is that as air is trying to force or ram itself into this pipe, it is doing so in a very small space. Maybe a little more will get in, but you won't really notice it. Luckily there is a way to get around this.
Let's say we used a 6" diameter pipe that faced forwards into the airstream. We can't just taper this down into a 3" pipe since the added air will just reverse itself. We'd actually get less air into the engine this way since we'd have to speed the air up as it enters the pipe. when we speed the air up, we lower it's pressure. That is not the goal. Less pressure is less air. If we feed the 6" pipe into an airbox or plenum chamber, we can alleviate this problem. We then feed the 3" pipe to the engine into this. The 6" inlet pipe has 4 times the area of the 3" pipe. When we bring all of this air into the airbox, the greater area or the airbox forces the air to slow down. When we slow air down, we increase it's pressure. This may confuse you when it comes to turbochargers or superchargers but I assure you this is what is happening in them too. The exception to this is the roots blower. It doesn't compress the air by slowing it down. It speeds it up and causes it to build up in the intake manifold. This is where the pressure is increased.
Back on topic. This airbox is now pressurized to some extent. Don't expect gains of supercharger proportions though. This higher pressure air is what the 3" pipe to the engine is feeding off of. Suddenly we have higher than ambient pressure entering the engine. We call this boost! Now we are ramming air into the engine. In order to utilize ram air, we must find a collection point for the air where it can build pressure. If you just have a filter in the airstream, you don't have this.
Racing Beat found that on their 1st generation Bonneville RX-7, a true functional ram air system added 3 mph to the top speed of the car. That doesn't sound like much but at 180 mph, it takes alot of power to go a little faster. This should still emphasize the fact though that you are not going to get incredible results from ram air. It is alot of effort for a little gain. If we could get even 1 psi of extra air into the engine, on a 200 hp engine that is still around 13 hp more. This is only at high speeds but it is more than you have now. If you find old pictures of the Racing Beat 1st gen. you will notice that there is a single 6" pipe that is fed air from the front of the car. It also dumps into a large plenum chamber in front of the throttlebody.
Next time you see a product that is marketed as "ram air" ask yourself, is it really?
12-05-2005, 10:03 AM
#3
The Professor
Yes, but you have to realize that anything that helps push air into the engine is going to be beneficial compared to just a vacuum type design.
Imagine you are trying to light a fire. You can either just let the coals sit there and use the air themselves, or you can blow on them. Which one is going to be hotter? Granted the coal and example is not directly congruent with an engine and its workings, but the principle is the same.
Even .001 positive pressure is better than having a negative pressure value.
Imagine you are trying to light a fire. You can either just let the coals sit there and use the air themselves, or you can blow on them. Which one is going to be hotter? Granted the coal and example is not directly congruent with an engine and its workings, but the principle is the same.
Even .001 positive pressure is better than having a negative pressure value.
12-05-2005, 11:12 AM
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My dad use to sell Pontiac's in the late 90's. He was told that the ram air hood on the Firebird produced in the neighborhood (I don't remeber exactly) 5hp at 120mph. I also remember reading that the ram air on the 550/575 Ferrari's produced 15hp at 150mph.
12-05-2005, 11:12 AM
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As usual I am going to be long winded about this. I'll try to be thorough but I may still miss something. Forgive me for any spelling errors. I still look at my hands while I type sometimes.
I can't say that I disagree with allot of what is said on the Z boards. For the most part it is marketing BS to sell more product but allow me to quantify that statement so I don't sound like I am going to contradict myself. Everyone always thinks in terms of full throttle horsepower gains. This is when the engine needs the most air so consequently a higher vehicle speed would be needed to see a beneficial power gain. This would probably begin in a very slight way above around 80 mph or so but only really start to get beneficial at higher speeds than this. Remember that if true ram air only took the Racing Beat Bonneville 1st gen from 180 to 183 mph, it didn't do a whole lot but it did do something. 3mph doesn't sound like much top speed increase but the horsepower needed to go even 1mph faster at those speeds is significant.
How about benefit at part throttle? If you get a gain here at usable speeds, is it still really marketing BS? The only marketing BS is the implication that you will feel a gain in power under normal driving conditions at full throttle. You won't. Many people expect to be able to feel a gain such as with a supercharger. The benefit is real but it isn't how or where most people expect it. Part throttle horsepower can see a benefit at lower speeds than at full throttle but still don't expect them to be at slow stop and go city speeds. It's still more of a benefit at freeway cruising. This is because the engine requires less air at lower rpm's and loads. It is very possible to get better gas mileage due to more efficient breathing at freeway speeds. The more throttle or rpm you have, the faster your forward speed needs to be to get a benefit. Most people don't think in terms of part throttle, which is why they don't grasp this. They say they don't care but if you have a street car, this is where you are most of the time. This is how you can still get a benefit even though you might not have any more peak horsepower at full throttle. Also remember you can't measure ram air on a dyno. Allot of people only believe in dyno numbers. It's an incomplete way of thinking.
As far as the comment that ram air needs to be moving at 420 mph to make 1 psi, that's not true and that comment shows a lack of understanding for what actually happens in a ram air system. If you don't have ram air you need to have your air filter in a 420 mph air stream in order to get 1 psi. Even then this is still technically inaccurate. I'll explain below. Ram air utilizes a force in order to increase air pressure. A turbo or supercharger exhibits a force on the air. This is how they compress it. Here's a simple example of force and pressure that everyone seems to get mixed up.
Some people like to use the analogy that if you stick your hand out the window of a moving car that you have pressure being exerted on it. This is not true. You have force being exerted on it but at static ambient pressure. By this reasoning we can see that even at 420 mph we still have ambient pressure but force went up. The key is to find a way to utilize this force to turn it into air pressure. At 420 mph, with a filter in the air stream it is still in ambient pressure air. The force of such fast moving air will cause a backup of air in the intake tube since it is slowing down. Some air is going around the filter but the extreme force of the air does push some extra in the intake. This causes it to slightly pressurize. Imagine how much pressure you could have if you had a true ram air system that used leverage on the air to increase its pressure further.
I can take a manometer or a magnehelic gauge (which I have done btw) and hold the end of the tube in the air stream. For an accurate reading of what the air pressure really is you stick a piece of foam over the end. It is porous enough that air flows through it easily. This breaks up any force from movement. It will still read ambient pressure of the air around it. Now you need to hold the open end of the tube out sideways from the moving air stream. You can move as fast as you want, the pressure gauge stays the same as the outside air. The foam does not hinder any airflow. It is just a stabilizing device. Now if you take the foam off the end of the tube and hold the open end into the air stream we will get a pressure reading as forward speed increases. On the magnehelic gauge it is about 1 psi at 60 mph and 2 psi at 70 mph. It goes up very quickly in relation to speed. How am I getting a pressure reading if ambient outside air pressure stays constant? Force is putting leverage on the air in the tube and doing work on it in the form of pressurizing it. Remember though that there is no airflow through the magnehelic gauge regardless of speed. If I bled off some airflow in the tube to simulate air ingestion into an engine the pressure on the gauge would go down. The larger the bleed off, the faster we'd have to move to see the gauge go back up.
So now we can see that in order to increase pressure we have to use some kind of force to exert leverage on the air. When the car is moving forward, we definitely have air force. By using an inlet into a properly designed air box, the incoming air will flow into the airbox where the area expands. This expansion slows the air down. When you slow air down, you increase it's pressure. The key to this box is that the inlet to the box is larger than the inlet to the engine. Obviously you can see that this ratio changes with throttle position which is why there is a bigger benefit at lower throttle settings in relation to speed. When we compress the air in the box, the air ingests the slightly compressed air from the high-pressure zone. Because of this there can be more airflow into the airbox without reversion out of it and still have a beneficial pressure. There will always be some air that may not want to go in the box and will go around but this is only because we don't have enough force to compress the air in order to keep it all in there. This is only natural though and doesn't mean we still don't have gains. If we didn't have a properly designed ram air box that converts this force to pressure, air would just go around the inlet. This is what happens with an air filter open to the air stream. This would require that you probably move at 420 mph and would require that the open end of the intake tube be facing into the air stream. The ram air box is the key to all of this. You don't have an increase in pressure unless you have a way to convert force to work by slowing the air down. Obviously ram air is a smaller power gain device but by no means useless.
What are a couple of other things that compress air by slowing it down? How about anything called a compressor such as a turbo or a supercharger? If you were to measure inlet airspeed into these devices and compare it to outlet airspeed, you'd see that the air coming out is moving slower than the air going in. This also assumes that the inlet and outlet areas are the same size. On a turbo or a supercharger the outlet is always smaller. It can be. Compressed air takes up less space. If the outlet airspeed is faster it's only due to a smaller flow area. The exception to this is the roots blower, which doesn't compress the air and consequently has the same inlet an outlet air speed. It utilizes force to send more into the engine. It forces air to stack up in the intake system and increase pressure. Sound familiar? A roots blower isn't efficient compared to other forms of forced induction but we can't say it does nothing. It does. So does ram air just on an even smaller scale.
Since nothing is free, every system requires some power to make more power. We all know this is true with a supercharger. It is still true with a turbo as well. We do utilize some free wasted exhaust energy but we still need to restrict the exhaust somewhat, which lowers power a bit over not having a turbo at all. The turbo is getting some of its power though from wasted energy. A supercharger takes all of its power from usable energy. A ram air system to uses energy. It is the energy of the forward motion of the vehicle through the air. However we don't need to restrict anything to affect the vehicle in any other way to realize ram air. It is the only system that truly does work to the air that doesn't also hinder us in some way. That's drag we had anyways. Drag didn't have to increase to get the gain.
As I said, ram air isn't a huge benefit but it definitely does work and at usable speeds. It all has to do with the leverage on the air in the form of a true proper designed ram air box as well as the demands of the engine. Just placing a filter in the air stream doesn't do it. Even drag over the body of the car does work to the air. There are some spots of higher pressure and some spots of lower pressure. Where do you think you should logically place the intake? I'd hope the higher-pressure zones at the front of the car and the base of the windshield. You will make more power this way than if the intake was on the middle of the hood. Now before anyone tells me that dragsters use inlets on top of the hoods, remember that they stick way up high into the air stream back into a high air force zone. The zones I am talking about are boundary effects from the cars aerodynamics. Also notice that the large intake scoops on dragsters have an expansion behind them before the air enters the engine. Coincidence? Nope. They are slowing down the air and increasing its pressure before it enters the engine. Their engines have such high airflow requirements that the inlet needs to be huge and it is. How much power do you think those guys would make without those huge scoops? How about just pointing them backwards? Same airflow ability but no air force to act on it. Power will go down. This is a real world example of ram air in use.
Some people will probably say that this is comparing a racecar to a street car. That's irrelevant. You can get a benefit on both. The air doesn't know what type of engine it is feeding. All the money, time, and testing is worthless if you don't know how to properly interpret the data you receive. I don't think a single lab worker would disagree with this. The same is true about allot of "observations" that people do with ram air. The concepts of force vs. pressure seem to be what mess people up the most.
To go back to one more topic from the Z board, if at 100 mph we got a 1.1% increase in mass airflow, how is that not useful again? Since power in an engine typically stays fairly close to airflow in terms of percentage increase, this would also be around a 1% increase in power. Too bad this still isn't enough information, as we don't know at what throttle level this is recorded. Remember my magnehelic gauge with no airflow at all had air force exhibit a pressure in the tube of 1 psi at only 60 mph. Depending on the engine load, size, and ram air design, there may be more or less than a 1% gain at this speed. We need more data. You can see how it's easy to base the wrong conclusions off of too little information.
Hopefully this helps and I've covered all the bases. I may have still missed something.
I can't say that I disagree with allot of what is said on the Z boards. For the most part it is marketing BS to sell more product but allow me to quantify that statement so I don't sound like I am going to contradict myself. Everyone always thinks in terms of full throttle horsepower gains. This is when the engine needs the most air so consequently a higher vehicle speed would be needed to see a beneficial power gain. This would probably begin in a very slight way above around 80 mph or so but only really start to get beneficial at higher speeds than this. Remember that if true ram air only took the Racing Beat Bonneville 1st gen from 180 to 183 mph, it didn't do a whole lot but it did do something. 3mph doesn't sound like much top speed increase but the horsepower needed to go even 1mph faster at those speeds is significant.
How about benefit at part throttle? If you get a gain here at usable speeds, is it still really marketing BS? The only marketing BS is the implication that you will feel a gain in power under normal driving conditions at full throttle. You won't. Many people expect to be able to feel a gain such as with a supercharger. The benefit is real but it isn't how or where most people expect it. Part throttle horsepower can see a benefit at lower speeds than at full throttle but still don't expect them to be at slow stop and go city speeds. It's still more of a benefit at freeway cruising. This is because the engine requires less air at lower rpm's and loads. It is very possible to get better gas mileage due to more efficient breathing at freeway speeds. The more throttle or rpm you have, the faster your forward speed needs to be to get a benefit. Most people don't think in terms of part throttle, which is why they don't grasp this. They say they don't care but if you have a street car, this is where you are most of the time. This is how you can still get a benefit even though you might not have any more peak horsepower at full throttle. Also remember you can't measure ram air on a dyno. Allot of people only believe in dyno numbers. It's an incomplete way of thinking.
As far as the comment that ram air needs to be moving at 420 mph to make 1 psi, that's not true and that comment shows a lack of understanding for what actually happens in a ram air system. If you don't have ram air you need to have your air filter in a 420 mph air stream in order to get 1 psi. Even then this is still technically inaccurate. I'll explain below. Ram air utilizes a force in order to increase air pressure. A turbo or supercharger exhibits a force on the air. This is how they compress it. Here's a simple example of force and pressure that everyone seems to get mixed up.
Some people like to use the analogy that if you stick your hand out the window of a moving car that you have pressure being exerted on it. This is not true. You have force being exerted on it but at static ambient pressure. By this reasoning we can see that even at 420 mph we still have ambient pressure but force went up. The key is to find a way to utilize this force to turn it into air pressure. At 420 mph, with a filter in the air stream it is still in ambient pressure air. The force of such fast moving air will cause a backup of air in the intake tube since it is slowing down. Some air is going around the filter but the extreme force of the air does push some extra in the intake. This causes it to slightly pressurize. Imagine how much pressure you could have if you had a true ram air system that used leverage on the air to increase its pressure further.
I can take a manometer or a magnehelic gauge (which I have done btw) and hold the end of the tube in the air stream. For an accurate reading of what the air pressure really is you stick a piece of foam over the end. It is porous enough that air flows through it easily. This breaks up any force from movement. It will still read ambient pressure of the air around it. Now you need to hold the open end of the tube out sideways from the moving air stream. You can move as fast as you want, the pressure gauge stays the same as the outside air. The foam does not hinder any airflow. It is just a stabilizing device. Now if you take the foam off the end of the tube and hold the open end into the air stream we will get a pressure reading as forward speed increases. On the magnehelic gauge it is about 1 psi at 60 mph and 2 psi at 70 mph. It goes up very quickly in relation to speed. How am I getting a pressure reading if ambient outside air pressure stays constant? Force is putting leverage on the air in the tube and doing work on it in the form of pressurizing it. Remember though that there is no airflow through the magnehelic gauge regardless of speed. If I bled off some airflow in the tube to simulate air ingestion into an engine the pressure on the gauge would go down. The larger the bleed off, the faster we'd have to move to see the gauge go back up.
So now we can see that in order to increase pressure we have to use some kind of force to exert leverage on the air. When the car is moving forward, we definitely have air force. By using an inlet into a properly designed air box, the incoming air will flow into the airbox where the area expands. This expansion slows the air down. When you slow air down, you increase it's pressure. The key to this box is that the inlet to the box is larger than the inlet to the engine. Obviously you can see that this ratio changes with throttle position which is why there is a bigger benefit at lower throttle settings in relation to speed. When we compress the air in the box, the air ingests the slightly compressed air from the high-pressure zone. Because of this there can be more airflow into the airbox without reversion out of it and still have a beneficial pressure. There will always be some air that may not want to go in the box and will go around but this is only because we don't have enough force to compress the air in order to keep it all in there. This is only natural though and doesn't mean we still don't have gains. If we didn't have a properly designed ram air box that converts this force to pressure, air would just go around the inlet. This is what happens with an air filter open to the air stream. This would require that you probably move at 420 mph and would require that the open end of the intake tube be facing into the air stream. The ram air box is the key to all of this. You don't have an increase in pressure unless you have a way to convert force to work by slowing the air down. Obviously ram air is a smaller power gain device but by no means useless.
What are a couple of other things that compress air by slowing it down? How about anything called a compressor such as a turbo or a supercharger? If you were to measure inlet airspeed into these devices and compare it to outlet airspeed, you'd see that the air coming out is moving slower than the air going in. This also assumes that the inlet and outlet areas are the same size. On a turbo or a supercharger the outlet is always smaller. It can be. Compressed air takes up less space. If the outlet airspeed is faster it's only due to a smaller flow area. The exception to this is the roots blower, which doesn't compress the air and consequently has the same inlet an outlet air speed. It utilizes force to send more into the engine. It forces air to stack up in the intake system and increase pressure. Sound familiar? A roots blower isn't efficient compared to other forms of forced induction but we can't say it does nothing. It does. So does ram air just on an even smaller scale.
Since nothing is free, every system requires some power to make more power. We all know this is true with a supercharger. It is still true with a turbo as well. We do utilize some free wasted exhaust energy but we still need to restrict the exhaust somewhat, which lowers power a bit over not having a turbo at all. The turbo is getting some of its power though from wasted energy. A supercharger takes all of its power from usable energy. A ram air system to uses energy. It is the energy of the forward motion of the vehicle through the air. However we don't need to restrict anything to affect the vehicle in any other way to realize ram air. It is the only system that truly does work to the air that doesn't also hinder us in some way. That's drag we had anyways. Drag didn't have to increase to get the gain.
As I said, ram air isn't a huge benefit but it definitely does work and at usable speeds. It all has to do with the leverage on the air in the form of a true proper designed ram air box as well as the demands of the engine. Just placing a filter in the air stream doesn't do it. Even drag over the body of the car does work to the air. There are some spots of higher pressure and some spots of lower pressure. Where do you think you should logically place the intake? I'd hope the higher-pressure zones at the front of the car and the base of the windshield. You will make more power this way than if the intake was on the middle of the hood. Now before anyone tells me that dragsters use inlets on top of the hoods, remember that they stick way up high into the air stream back into a high air force zone. The zones I am talking about are boundary effects from the cars aerodynamics. Also notice that the large intake scoops on dragsters have an expansion behind them before the air enters the engine. Coincidence? Nope. They are slowing down the air and increasing its pressure before it enters the engine. Their engines have such high airflow requirements that the inlet needs to be huge and it is. How much power do you think those guys would make without those huge scoops? How about just pointing them backwards? Same airflow ability but no air force to act on it. Power will go down. This is a real world example of ram air in use.
Some people will probably say that this is comparing a racecar to a street car. That's irrelevant. You can get a benefit on both. The air doesn't know what type of engine it is feeding. All the money, time, and testing is worthless if you don't know how to properly interpret the data you receive. I don't think a single lab worker would disagree with this. The same is true about allot of "observations" that people do with ram air. The concepts of force vs. pressure seem to be what mess people up the most.
To go back to one more topic from the Z board, if at 100 mph we got a 1.1% increase in mass airflow, how is that not useful again? Since power in an engine typically stays fairly close to airflow in terms of percentage increase, this would also be around a 1% increase in power. Too bad this still isn't enough information, as we don't know at what throttle level this is recorded. Remember my magnehelic gauge with no airflow at all had air force exhibit a pressure in the tube of 1 psi at only 60 mph. Depending on the engine load, size, and ram air design, there may be more or less than a 1% gain at this speed. We need more data. You can see how it's easy to base the wrong conclusions off of too little information.
Hopefully this helps and I've covered all the bases. I may have still missed something.
Last edited by rotarygod; 12-05-2005 at 11:22 AM.
12-05-2005, 11:25 AM
#8
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Damn I made alot of spelling errors! Oh well. I'm not going to take the time to go back to fix them all.
I will add one more thought though. As we all know the street can radiate an awful lot of heat in the summer. As we get higher above the surface, the air gets cooler to an extent. How do you think your power would be affected with an intake near ground level vs one a little higher up and by higher I mean as little as a foot higher? I'll let everyone ponder that one. Here's a hint. The Mazda Courage race car has cooling issues. It has a decent amount of airflow to the radiators but almost all of the air is drawn off of the ground from underneath the car. They are recording cooling air temperatures of 10-15 degrees different based on inlet location alone. Something to think about the next time someone wants to place their filter under the car vs the grille area.
I will add one more thought though. As we all know the street can radiate an awful lot of heat in the summer. As we get higher above the surface, the air gets cooler to an extent. How do you think your power would be affected with an intake near ground level vs one a little higher up and by higher I mean as little as a foot higher? I'll let everyone ponder that one. Here's a hint. The Mazda Courage race car has cooling issues. It has a decent amount of airflow to the radiators but almost all of the air is drawn off of the ground from underneath the car. They are recording cooling air temperatures of 10-15 degrees different based on inlet location alone. Something to think about the next time someone wants to place their filter under the car vs the grille area.
Last edited by rotarygod; 12-05-2005 at 11:32 AM.
12-05-2005, 06:23 PM
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Originally Posted by rotarygod
Part throttle horsepower can see a benefit at lower speeds than at full throttle but still don't expect them to be at slow stop and go city speeds. It's still more of a benefit at freeway cruising. This is because the engine requires less air at lower rpm's and loads. It is very possible to get better gas mileage due to more efficient breathing at freeway speeds. The more throttle or rpm you have, the faster your forward speed needs to be to get a benefit. Most people don't think in terms of part throttle, which is why they don't grasp this. They say they don't care but if you have a street car, this is where you are most of the time. This is how you can still get a benefit even though you might not have any more peak horsepower at full throttle. Also remember you can't measure ram air on a dyno. Allot of people only believe in dyno numbers. It's an incomplete way of thinking.
Now add a "ram air" scoop. At 70mph and low throttle you would expect to be able to see a slight pressure rise as more air is being supplied then needed because of the restriction in the throttle. If any positive effects were seen you would expect a more efficient intake efficiency and an increase airflow at that 35% throttle position. But we are keeping a constant speed through supplying a constant amount of power, and more air in means more fuel will be dumped in which will create more power - which means the throttle will start to close slightly to maybe 34 or 33% open, and thus create more restriction in the intake and cause you to loose a good amount of the small gains you were getting.
12-05-2005, 08:18 PM
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First off more air does not always mean more power and worse gas mileage. You need to put it into context. This actually may or may not be true depending on the scenario. In the case of how this works in this application, you do gain some efficency and mileage at freeway speeds but you will not see any full throttle increases until very fast speeds are achieved. As far as the throttle closing a bit, this would only further raise pressure in the airbox at speed and not decrease it. Air pressure could potentially even stay the same but it won't go down.
An air filter in the system is irrelevant so why the bs flag is raised shows ignorance to how airflow in relation to pressure actually works. Don't believe me? So you are saying that an air filter placed in a high pressure zone and another one in a low pressure zone will feed the exact same amount of air at the same pressure as each other? How is the filter some magical device that equalizes air pressure to a constant? It has nothing to do with physically blowing more air in the form of velocity into the air filter. The whole point is to increase air pressure in the region around where the air intake/filter picks up the air. So basically I am going to lower your bs flag since it is flying at the wrong time. If an air filter is an issue to pressure and has an effect then I am going to climb Mt. Everest with an air filter over my face so I can breathe normal pressure sea level air and not the air pressure around me. Somehow I don't think that will work. It's not about flow into the filter, it's about pressure. The key to your sentance is "low speeds". Air filter or not, you won't have a usable effect at low speeds.
Make a simple manometer out of vinyl tubing and run some simple experiments to see how it all works. It's pretty neat. There's no magic to it and it is very real.
An air filter in the system is irrelevant so why the bs flag is raised shows ignorance to how airflow in relation to pressure actually works. Don't believe me? So you are saying that an air filter placed in a high pressure zone and another one in a low pressure zone will feed the exact same amount of air at the same pressure as each other? How is the filter some magical device that equalizes air pressure to a constant? It has nothing to do with physically blowing more air in the form of velocity into the air filter. The whole point is to increase air pressure in the region around where the air intake/filter picks up the air. So basically I am going to lower your bs flag since it is flying at the wrong time. If an air filter is an issue to pressure and has an effect then I am going to climb Mt. Everest with an air filter over my face so I can breathe normal pressure sea level air and not the air pressure around me. Somehow I don't think that will work. It's not about flow into the filter, it's about pressure. The key to your sentance is "low speeds". Air filter or not, you won't have a usable effect at low speeds.
Make a simple manometer out of vinyl tubing and run some simple experiments to see how it all works. It's pretty neat. There's no magic to it and it is very real.
12-05-2005, 08:23 PM
#13
I have done those experiments in the lab as a budding mechanical engineer, but in the context of the magnitude of the result for this particular real world situation it doesn't amount to squat
it will be even less so with an air filter in the system than without, the fact that the theory is sound is irrelevant if the real world result is for all intents and purposes immeasurable or insignificant
and most knoiwledgable racing engineers don't rely on ram air, they instead take air from a high pressure point acting on the body, like at the base of the windshield
it will be even less so with an air filter in the system than without, the fact that the theory is sound is irrelevant if the real world result is for all intents and purposes immeasurable or insignificant
and most knoiwledgable racing engineers don't rely on ram air, they instead take air from a high pressure point acting on the body, like at the base of the windshield
12-07-2005, 03:07 PM
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Yeh..this thread is giving me a bad thermo relapse from college. With regards to the Racing Beat intake, I dont think the Air duct is going to give you the ram air effect, but since it draws air from the front of the vehicle,the air is considerably cooler than the stock air box, but like the lecture above says....ram air effect...not likely
12-07-2005, 04:42 PM
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In addition
Originally Posted by rotarygod
First off more air does not always mean more power and worse gas mileage. You need to put it into context. This actually may or may not be true depending on the scenario. In the case of how this works in this application, you do gain some efficency and mileage at freeway speeds but you will not see any full throttle increases until very fast speeds are achieved. As far as the throttle closing a bit, this would only further raise pressure in the airbox at speed and not decrease it. Air pressure could potentially even stay the same but it won't go down.
An air filter in the system is irrelevant so why the bs flag is raised shows ignorance to how airflow in relation to pressure actually works. Don't believe me? So you are saying that an air filter placed in a high pressure zone and another one in a low pressure zone will feed the exact same amount of air at the same pressure as each other? How is the filter some magical device that equalizes air pressure to a constant? It has nothing to do with physically blowing more air in the form of velocity into the air filter. The whole point is to increase air pressure in the region around where the air intake/filter picks up the air. So basically I am going to lower your bs flag since it is flying at the wrong time. If an air filter is an issue to pressure and has an effect then I am going to climb Mt. Everest with an air filter over my face so I can breathe normal pressure sea level air and not the air pressure around me. Somehow I don't think that will work. It's not about flow into the filter, it's about pressure. The key to your sentance is "low speeds". Air filter or not, you won't have a usable effect at low speeds.
Make a simple manometer out of vinyl tubing and run some simple experiments to see how it all works. It's pretty neat. There's no magic to it and it is very real.
An air filter in the system is irrelevant so why the bs flag is raised shows ignorance to how airflow in relation to pressure actually works. Don't believe me? So you are saying that an air filter placed in a high pressure zone and another one in a low pressure zone will feed the exact same amount of air at the same pressure as each other? How is the filter some magical device that equalizes air pressure to a constant? It has nothing to do with physically blowing more air in the form of velocity into the air filter. The whole point is to increase air pressure in the region around where the air intake/filter picks up the air. So basically I am going to lower your bs flag since it is flying at the wrong time. If an air filter is an issue to pressure and has an effect then I am going to climb Mt. Everest with an air filter over my face so I can breathe normal pressure sea level air and not the air pressure around me. Somehow I don't think that will work. It's not about flow into the filter, it's about pressure. The key to your sentance is "low speeds". Air filter or not, you won't have a usable effect at low speeds.
Make a simple manometer out of vinyl tubing and run some simple experiments to see how it all works. It's pretty neat. There's no magic to it and it is very real.
As a practical observation, sail boats small or large capture the movement of the air for propulsion as does a wind mill or even a Turbo Charger Compressor. To move a sail boat or turbo charger compressor, all one needs is a pressure differential. That is all wind is. The result of a pressure differential.
While the turbo charger creates artificial wind from the force of the exhaust to created a pressure differential to move a higher volume of air into the intake over NA, why is it so difficult to consider the value of a duct in the nose of a car to capture the higher force of the air and feed it into the intake using the same type of pressure differential.
Observing this discussion it appears the challenge is that the effect of a ram duct cannot be measured while the car is standing still on a Dyno like a turbo charger can.
Well for a practical experiment, next time the wind is blowing say 30MPH or better, go out and stand with your face to the wind and open your mouth and try to control the volume of air being forced into your mouth and down your throat. The pressure of the air created by the wind is greater that the pressure in your mouth, and it feels like you are gagging on the wind. Think of the force of the wind at 80 or 110 MPH.
A wind of 50 MPH has enough force to cause minor damage and as the velocity of natural wind increases, the force of that wind also increases.
So, say on a road track straightaway, with the speed increasing well over 100MPH is it that inconceivable that forcing air moving at that velocity down the intake of the engine would naturally provide the engine additional air it would not normally get using just vacuum, since vacuum at full acceleration is all but 0-CFM. So how much CFM is captured at 50MPH plus and forced into the plenum which is at a lower pressure with no where to go but into the engine.
So, if the incoming CFM is at a greater pressure than the air in the plenum would that not work like a type of super charger forcing the air into the engine when the throttle body opens up allowing a air at a positive pressure into a negative or neutral pressure zone?
It is just an observation, but if that is not the way it actually works then sail boats don’t really move, and there really is no wind, it is all just an illusion.
12-07-2005, 07:34 PM
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I'd really like to read this entire thread, but can anyone give me a synopsis and/or conclusion as to whether the RB intake, for example, really helps or not?
12-07-2005, 07:42 PM
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You can't take a few minutes to read 2 pages???????? It woudln't have taken you much longer to read the thread than it did to post the message....
Originally Posted by Raptor2k
I'd really like to read this entire thread, but can anyone give me a synopsis and/or conclusion as to whether the RB intake, for example, really helps or not?
12-07-2005, 07:45 PM
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Originally Posted by guy321
You can't take a few minutes to read 2 pages???????? It woudln't have taken you much longer to read the thread than it did to post the message....
12-07-2005, 07:47 PM
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Originally Posted by zoom44
at speed the rb intake produces a slight ram-like effect that imho increases throttle response
I always filter out about 3/4 of what RG says :D
09-23-2012, 01:50 AM
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As usual I am going to be long winded about this. I'll try to be thorough but I may still miss something. Forgive me for any spelling errors. I still look at my hands while I type sometimes.
I can't say that I disagree with allot of what is said on the Z boards. For the most part it is marketing BS to sell more product but allow me to quantify that statement so I don't sound like I am going to contradict myself. Everyone always thinks in terms of full throttle horsepower gains. This is when the engine needs the most air so consequently a higher vehicle speed would be needed to see a beneficial power gain. This would probably begin in a very slight way above around 80 mph or so but only really start to get beneficial at higher speeds than this. Remember that if true ram air only took the Racing Beat Bonneville 1st gen from 180 to 183 mph, it didn't do a whole lot but it did do something. 3mph doesn't sound like much top speed increase but the horsepower needed to go even 1mph faster at those speeds is significant.
How about benefit at part throttle? If you get a gain here at usable speeds, is it still really marketing BS? The only marketing BS is the implication that you will feel a gain in power under normal driving conditions at full throttle. You won't. Many people expect to be able to feel a gain such as with a supercharger. The benefit is real but it isn't how or where most people expect it. Part throttle horsepower can see a benefit at lower speeds than at full throttle but still don't expect them to be at slow stop and go city speeds. It's still more of a benefit at freeway cruising. This is because the engine requires less air at lower rpm's and loads. It is very possible to get better gas mileage due to more efficient breathing at freeway speeds. The more throttle or rpm you have, the faster your forward speed needs to be to get a benefit. Most people don't think in terms of part throttle, which is why they don't grasp this. They say they don't care but if you have a street car, this is where you are most of the time. This is how you can still get a benefit even though you might not have any more peak horsepower at full throttle. Also remember you can't measure ram air on a dyno. Allot of people only believe in dyno numbers. It's an incomplete way of thinking.
As far as the comment that ram air needs to be moving at 420 mph to make 1 psi, that's not true and that comment shows a lack of understanding for what actually happens in a ram air system. If you don't have ram air you need to have your air filter in a 420 mph air stream in order to get 1 psi. Even then this is still technically inaccurate. I'll explain below. Ram air utilizes a force in order to increase air pressure. A turbo or supercharger exhibits a force on the air. This is how they compress it. Here's a simple example of force and pressure that everyone seems to get mixed up.
Some people like to use the analogy that if you stick your hand out the window of a moving car that you have pressure being exerted on it. This is not true. You have force being exerted on it but at static ambient pressure. By this reasoning we can see that even at 420 mph we still have ambient pressure but force went up. The key is to find a way to utilize this force to turn it into air pressure. At 420 mph, with a filter in the air stream it is still in ambient pressure air. The force of such fast moving air will cause a backup of air in the intake tube since it is slowing down. Some air is going around the filter but the extreme force of the air does push some extra in the intake. This causes it to slightly pressurize. Imagine how much pressure you could have if you had a true ram air system that used leverage on the air to increase its pressure further.
I can take a manometer or a magnehelic gauge (which I have done btw) and hold the end of the tube in the air stream. For an accurate reading of what the air pressure really is you stick a piece of foam over the end. It is porous enough that air flows through it easily. This breaks up any force from movement. It will still read ambient pressure of the air around it. Now you need to hold the open end of the tube out sideways from the moving air stream. You can move as fast as you want, the pressure gauge stays the same as the outside air. The foam does not hinder any airflow. It is just a stabilizing device. Now if you take the foam off the end of the tube and hold the open end into the air stream we will get a pressure reading as forward speed increases. On the magnehelic gauge it is about 1 psi at 60 mph and 2 psi at 70 mph. It goes up very quickly in relation to speed. How am I getting a pressure reading if ambient outside air pressure stays constant? Force is putting leverage on the air in the tube and doing work on it in the form of pressurizing it. Remember though that there is no airflow through the magnehelic gauge regardless of speed. If I bled off some airflow in the tube to simulate air ingestion into an engine the pressure on the gauge would go down. The larger the bleed off, the faster we'd have to move to see the gauge go back up.
So now we can see that in order to increase pressure we have to use some kind of force to exert leverage on the air. When the car is moving forward, we definitely have air force. By using an inlet into a properly designed air box, the incoming air will flow into the airbox where the area expands. This expansion slows the air down. When you slow air down, you increase it's pressure. The key to this box is that the inlet to the box is larger than the inlet to the engine. Obviously you can see that this ratio changes with throttle position which is why there is a bigger benefit at lower throttle settings in relation to speed. When we compress the air in the box, the air ingests the slightly compressed air from the high-pressure zone. Because of this there can be more airflow into the airbox without reversion out of it and still have a beneficial pressure. There will always be some air that may not want to go in the box and will go around but this is only because we don't have enough force to compress the air in order to keep it all in there. This is only natural though and doesn't mean we still don't have gains. If we didn't have a properly designed ram air box that converts this force to pressure, air would just go around the inlet. This is what happens with an air filter open to the air stream. This would require that you probably move at 420 mph and would require that the open end of the intake tube be facing into the air stream. The ram air box is the key to all of this. You don't have an increase in pressure unless you have a way to convert force to work by slowing the air down. Obviously ram air is a smaller power gain device but by no means useless.
What are a couple of other things that compress air by slowing it down? How about anything called a compressor such as a turbo or a supercharger? If you were to measure inlet airspeed into these devices and compare it to outlet airspeed, you'd see that the air coming out is moving slower than the air going in. This also assumes that the inlet and outlet areas are the same size. On a turbo or a supercharger the outlet is always smaller. It can be. Compressed air takes up less space. If the outlet airspeed is faster it's only due to a smaller flow area. The exception to this is the roots blower, which doesn't compress the air and consequently has the same inlet an outlet air speed. It utilizes force to send more into the engine. It forces air to stack up in the intake system and increase pressure. Sound familiar? A roots blower isn't efficient compared to other forms of forced induction but we can't say it does nothing. It does. So does ram air just on an even smaller scale.
Since nothing is free, every system requires some power to make more power. We all know this is true with a supercharger. It is still true with a turbo as well. We do utilize some free wasted exhaust energy but we still need to restrict the exhaust somewhat, which lowers power a bit over not having a turbo at all. The turbo is getting some of its power though from wasted energy. A supercharger takes all of its power from usable energy. A ram air system to uses energy. It is the energy of the forward motion of the vehicle through the air. However we don't need to restrict anything to affect the vehicle in any other way to realize ram air. It is the only system that truly does work to the air that doesn't also hinder us in some way. That's drag we had anyways. Drag didn't have to increase to get the gain.
As I said, ram air isn't a huge benefit but it definitely does work and at usable speeds. It all has to do with the leverage on the air in the form of a true proper designed ram air box as well as the demands of the engine. Just placing a filter in the air stream doesn't do it. Even drag over the body of the car does work to the air. There are some spots of higher pressure and some spots of lower pressure. Where do you think you should logically place the intake? I'd hope the higher-pressure zones at the front of the car and the base of the windshield. You will make more power this way than if the intake was on the middle of the hood. Now before anyone tells me that dragsters use inlets on top of the hoods, remember that they stick way up high into the air stream back into a high air force zone. The zones I am talking about are boundary effects from the cars aerodynamics. Also notice that the large intake scoops on dragsters have an expansion behind them before the air enters the engine. Coincidence? Nope. They are slowing down the air and increasing its pressure before it enters the engine. Their engines have such high airflow requirements that the inlet needs to be huge and it is. How much power do you think those guys would make without those huge scoops? How about just pointing them backwards? Same airflow ability but no air force to act on it. Power will go down. This is a real world example of ram air in use.
Some people will probably say that this is comparing a racecar to a street car. That's irrelevant. You can get a benefit on both. The air doesn't know what type of engine it is feeding. All the money, time, and testing is worthless if you don't know how to properly interpret the data you receive. I don't think a single lab worker would disagree with this. The same is true about allot of "observations" that people do with ram air. The concepts of force vs. pressure seem to be what mess people up the most.
To go back to one more topic from the Z board, if at 100 mph we got a 1.1% increase in mass airflow, how is that not useful again? Since power in an engine typically stays fairly close to airflow in terms of percentage increase, this would also be around a 1% increase in power. Too bad this still isn't enough information, as we don't know at what throttle level this is recorded. Remember my magnehelic gauge with no airflow at all had air force exhibit a pressure in the tube of 1 psi at only 60 mph. Depending on the engine load, size, and ram air design, there may be more or less than a 1% gain at this speed. We need more data. You can see how it's easy to base the wrong conclusions off of too little information.
Hopefully this helps and I've covered all the bases. I may have still missed something.
I can't say that I disagree with allot of what is said on the Z boards. For the most part it is marketing BS to sell more product but allow me to quantify that statement so I don't sound like I am going to contradict myself. Everyone always thinks in terms of full throttle horsepower gains. This is when the engine needs the most air so consequently a higher vehicle speed would be needed to see a beneficial power gain. This would probably begin in a very slight way above around 80 mph or so but only really start to get beneficial at higher speeds than this. Remember that if true ram air only took the Racing Beat Bonneville 1st gen from 180 to 183 mph, it didn't do a whole lot but it did do something. 3mph doesn't sound like much top speed increase but the horsepower needed to go even 1mph faster at those speeds is significant.
How about benefit at part throttle? If you get a gain here at usable speeds, is it still really marketing BS? The only marketing BS is the implication that you will feel a gain in power under normal driving conditions at full throttle. You won't. Many people expect to be able to feel a gain such as with a supercharger. The benefit is real but it isn't how or where most people expect it. Part throttle horsepower can see a benefit at lower speeds than at full throttle but still don't expect them to be at slow stop and go city speeds. It's still more of a benefit at freeway cruising. This is because the engine requires less air at lower rpm's and loads. It is very possible to get better gas mileage due to more efficient breathing at freeway speeds. The more throttle or rpm you have, the faster your forward speed needs to be to get a benefit. Most people don't think in terms of part throttle, which is why they don't grasp this. They say they don't care but if you have a street car, this is where you are most of the time. This is how you can still get a benefit even though you might not have any more peak horsepower at full throttle. Also remember you can't measure ram air on a dyno. Allot of people only believe in dyno numbers. It's an incomplete way of thinking.
As far as the comment that ram air needs to be moving at 420 mph to make 1 psi, that's not true and that comment shows a lack of understanding for what actually happens in a ram air system. If you don't have ram air you need to have your air filter in a 420 mph air stream in order to get 1 psi. Even then this is still technically inaccurate. I'll explain below. Ram air utilizes a force in order to increase air pressure. A turbo or supercharger exhibits a force on the air. This is how they compress it. Here's a simple example of force and pressure that everyone seems to get mixed up.
Some people like to use the analogy that if you stick your hand out the window of a moving car that you have pressure being exerted on it. This is not true. You have force being exerted on it but at static ambient pressure. By this reasoning we can see that even at 420 mph we still have ambient pressure but force went up. The key is to find a way to utilize this force to turn it into air pressure. At 420 mph, with a filter in the air stream it is still in ambient pressure air. The force of such fast moving air will cause a backup of air in the intake tube since it is slowing down. Some air is going around the filter but the extreme force of the air does push some extra in the intake. This causes it to slightly pressurize. Imagine how much pressure you could have if you had a true ram air system that used leverage on the air to increase its pressure further.
I can take a manometer or a magnehelic gauge (which I have done btw) and hold the end of the tube in the air stream. For an accurate reading of what the air pressure really is you stick a piece of foam over the end. It is porous enough that air flows through it easily. This breaks up any force from movement. It will still read ambient pressure of the air around it. Now you need to hold the open end of the tube out sideways from the moving air stream. You can move as fast as you want, the pressure gauge stays the same as the outside air. The foam does not hinder any airflow. It is just a stabilizing device. Now if you take the foam off the end of the tube and hold the open end into the air stream we will get a pressure reading as forward speed increases. On the magnehelic gauge it is about 1 psi at 60 mph and 2 psi at 70 mph. It goes up very quickly in relation to speed. How am I getting a pressure reading if ambient outside air pressure stays constant? Force is putting leverage on the air in the tube and doing work on it in the form of pressurizing it. Remember though that there is no airflow through the magnehelic gauge regardless of speed. If I bled off some airflow in the tube to simulate air ingestion into an engine the pressure on the gauge would go down. The larger the bleed off, the faster we'd have to move to see the gauge go back up.
So now we can see that in order to increase pressure we have to use some kind of force to exert leverage on the air. When the car is moving forward, we definitely have air force. By using an inlet into a properly designed air box, the incoming air will flow into the airbox where the area expands. This expansion slows the air down. When you slow air down, you increase it's pressure. The key to this box is that the inlet to the box is larger than the inlet to the engine. Obviously you can see that this ratio changes with throttle position which is why there is a bigger benefit at lower throttle settings in relation to speed. When we compress the air in the box, the air ingests the slightly compressed air from the high-pressure zone. Because of this there can be more airflow into the airbox without reversion out of it and still have a beneficial pressure. There will always be some air that may not want to go in the box and will go around but this is only because we don't have enough force to compress the air in order to keep it all in there. This is only natural though and doesn't mean we still don't have gains. If we didn't have a properly designed ram air box that converts this force to pressure, air would just go around the inlet. This is what happens with an air filter open to the air stream. This would require that you probably move at 420 mph and would require that the open end of the intake tube be facing into the air stream. The ram air box is the key to all of this. You don't have an increase in pressure unless you have a way to convert force to work by slowing the air down. Obviously ram air is a smaller power gain device but by no means useless.
What are a couple of other things that compress air by slowing it down? How about anything called a compressor such as a turbo or a supercharger? If you were to measure inlet airspeed into these devices and compare it to outlet airspeed, you'd see that the air coming out is moving slower than the air going in. This also assumes that the inlet and outlet areas are the same size. On a turbo or a supercharger the outlet is always smaller. It can be. Compressed air takes up less space. If the outlet airspeed is faster it's only due to a smaller flow area. The exception to this is the roots blower, which doesn't compress the air and consequently has the same inlet an outlet air speed. It utilizes force to send more into the engine. It forces air to stack up in the intake system and increase pressure. Sound familiar? A roots blower isn't efficient compared to other forms of forced induction but we can't say it does nothing. It does. So does ram air just on an even smaller scale.
Since nothing is free, every system requires some power to make more power. We all know this is true with a supercharger. It is still true with a turbo as well. We do utilize some free wasted exhaust energy but we still need to restrict the exhaust somewhat, which lowers power a bit over not having a turbo at all. The turbo is getting some of its power though from wasted energy. A supercharger takes all of its power from usable energy. A ram air system to uses energy. It is the energy of the forward motion of the vehicle through the air. However we don't need to restrict anything to affect the vehicle in any other way to realize ram air. It is the only system that truly does work to the air that doesn't also hinder us in some way. That's drag we had anyways. Drag didn't have to increase to get the gain.
As I said, ram air isn't a huge benefit but it definitely does work and at usable speeds. It all has to do with the leverage on the air in the form of a true proper designed ram air box as well as the demands of the engine. Just placing a filter in the air stream doesn't do it. Even drag over the body of the car does work to the air. There are some spots of higher pressure and some spots of lower pressure. Where do you think you should logically place the intake? I'd hope the higher-pressure zones at the front of the car and the base of the windshield. You will make more power this way than if the intake was on the middle of the hood. Now before anyone tells me that dragsters use inlets on top of the hoods, remember that they stick way up high into the air stream back into a high air force zone. The zones I am talking about are boundary effects from the cars aerodynamics. Also notice that the large intake scoops on dragsters have an expansion behind them before the air enters the engine. Coincidence? Nope. They are slowing down the air and increasing its pressure before it enters the engine. Their engines have such high airflow requirements that the inlet needs to be huge and it is. How much power do you think those guys would make without those huge scoops? How about just pointing them backwards? Same airflow ability but no air force to act on it. Power will go down. This is a real world example of ram air in use.
Some people will probably say that this is comparing a racecar to a street car. That's irrelevant. You can get a benefit on both. The air doesn't know what type of engine it is feeding. All the money, time, and testing is worthless if you don't know how to properly interpret the data you receive. I don't think a single lab worker would disagree with this. The same is true about allot of "observations" that people do with ram air. The concepts of force vs. pressure seem to be what mess people up the most.
To go back to one more topic from the Z board, if at 100 mph we got a 1.1% increase in mass airflow, how is that not useful again? Since power in an engine typically stays fairly close to airflow in terms of percentage increase, this would also be around a 1% increase in power. Too bad this still isn't enough information, as we don't know at what throttle level this is recorded. Remember my magnehelic gauge with no airflow at all had air force exhibit a pressure in the tube of 1 psi at only 60 mph. Depending on the engine load, size, and ram air design, there may be more or less than a 1% gain at this speed. We need more data. You can see how it's easy to base the wrong conclusions off of too little information.
Hopefully this helps and I've covered all the bases. I may have still missed something.
Had to bump this thread lol
First off if you're reading this RG, I know it gives u pleasure to think about these things but thanks for also sharing them, and know that some people do intently read your statements.
Anyways, I have relocated my battery so now I have some engine bay space to play with right next to the airbox.
What if i enlarged my airbox let's say for argument's sake, doubled it.... according to what RG is saying IF i understood correctly, would I increase pressure even more so and therefore make more power?
so many question, don't really understand pressure that well to begin with...
RG if you're reading
You mentioned earlier:
Since we really want our intake air to be going no faster than 180 ft/sec
Why? Some quick bogus math based on my imaginary dimensions of the rotors tells me the outer rotor edges go around that speed (120mph) at ca. 9k rpm, is this why?
And even if let's say it was possible for intake air to move faster than this (doubt it is considering the convolutions the air has to travel through) wouldn't that be beneficial given that the air would compress when hitting the slower moving rotor and create higher pressure?
Also even though you might have pressurized air in the airbox, when the rotor reaches around 9k rpm and is hypothetically taking in air at approximately 120 mph roughly the speed of the rotor itself, wouldn't that mean that the air is being sucked from the airbox at about that speed, and wouldn't that then create lower pressure again and negligate the pressurized airbox air benefits.
Back to the enlarged airbox, it seems as if when you first get back on WOT at speed and after having been at partial throttle it would really have a great effect since you have a verly large volume of pressurized air waiting readily to be sucked in to the engine.
