ram air a myth?

What do you all think?

ram air myth (http://www.vetteguru.com/ramair/)

I believe it - although my 96 WS.6 has basically the same exhaust as the regular f-car, except for the tips.

I also think it was proven by the CAI kits gaining 20 hp (dyno proven) on the regular lt1 f-cars.

Joe

I totally agree with the ram air myth. Most production sports cars ( I don't include Ferrari's, Porsche, Lambos, or other excotics) wont even see speeds above 150. Thats about when the ram air effect may gain you 2 or 3 horse's.
And when the engine can take advantage of air speed around it to provide a ramming affect, its not even worth it, because when your going 160+ your more worried about aerodynamics, and drag caused by a ram air scoop, than adding 10-20hp.

I will say that ram air scoops will help performance for a few reasons.
One, a properly designed system will eliminate alot of the sharp turns the intake air must take to reach the engine that are normally found on a non ram air model.
Two, the majority of the time, the under hood temps of a car are much higher than outside air is. Bringing in cooler air into the engine will inscrease performance almost 100% of the time. So the ram air scoops add a place where cold air induction can be used.
And if your taking your modded Z06 to the track and running 175+ down teh back straight, yes ram air will help you pick up a few horses, but I don't think most people will notice it, especially at 175 plus.
Another thing, it is very hard to test the performance increase of a ram air system, as on a dyno the car is staionary, and even with a huge fan blowing air on the front of the car it still won't simulate accuratley the ram air affect.

So I say, unless you really want the ram air hood (which looks freaking wicked on a black trans am!!), spend your money on another option.

Hunter

I was skeptical but my first drive after installing FTRA made me a believer. The car pulls harder and harder the faster you go and the increased pull starts well before reaching triple digit speeds. Throttle response has also improved throughout the rev range (at any speed). Ram air has a mild supercharging effect and you can really feel the power! :thumb:

There's a good example of the calculation of the potential gain, using "velocity head" as the basis, in the "Automotive Math Handbook" by Forbes Aird. He demonstrates that the potential pressure gain is about 1% at 100mph. That means in a stock LT1/LS1, you are looking at about 3HP. However, in a 500HP setup, that's 5HP at 100mph, and since the gain is rpoportional to the square of the speed, that's 10HP at 141mph. Whether that's of value depends on how badly you need that extra 5 or 10HP.

Of course that same "square of the speed" rule means that you are only seeing a potential 3/4HP at 50mph.

It is also apparent that the shape of the 4th Gen Ram Air intake, both the LT1 and the LS1 is far from ideal, and the presence of the baffles and the "tortuous path" they prescribe may well negate all gain.

However, open those baffles up and reshape the ducting, and its a bit more "real".

Exactly what injuneer said.

I know how the ram air birds feel, they definatley pull harder than a normal bird, but its not because of the supercharging affect. But as Injuneer said, if you have a 750 hp engine it might matter.

Hunter

750 hp? It is well known FTRA is good for a few miles per hour in the quarter.

It doesnt RAM air past the filter, I mean there are freaking walls in the hood that block any sort of air flow that would have enough force to ram anything, but it is like cold air once you are moving atleast 25 mph and looks badass, I know its cold air becase I htested it out with datamaster and when I was sitting the air temps started to rise and I started moving and they quickly went down to around the outside temperature. Either is fine I would say ram air looks badass adn gives gains when your moving as well as gives a strait shot to the tb with less heat soak, maybe not so much from the factory since the filter is so covered by the plastic crap, but if money is a concern and you really dont care for a new hood CAI all the way...

There certainly isn't much ram-air effect below 100 MPH, but testing on motorcycles by Performance Bikes and Sport Rider have proven that it does exist at higher speeds. Both mags put a variety of bikes on a dyno and ran them up while measuring the airbox pressure, and then did the same with the bikes running around a track at top speed. Well-designed systems using diverging tracts and a large ratio of airbox to cylinder volume showed some not-insignificant gains (I seem to remember that the Hayabusa showed a pressure increase of about 5%), while bikes with poor tract design or small airboxes showed no increase or even a decrease (such as the Suzuki TL1000R).

But, yea, the cold-air effect is certainly what's most noticable at "mortal" speeds.

Originally posted by lt4 fd
It doesnt RAM air past the filter,
The concept of velocity head demonstrates the pressure increase at the scoop inlet. That pressure increase may not all be "recovered", as a function of the shape of the inlet. But pressure is pressure, and if you have a higher pressure on one side of the baffle, or of the filter element, you will have a higher pressure on the other side of it.

I mean there are freaking walls in the hood that block any sort of air flow that would have enough force to ram anything,
depends (http://cjcfo.fbody.com/members/injuneerzz@aol.com/PhotosL/DCP03644a.jpg)

but it is like cold air once you are moving atleast 25 mph and looks badass, I know its cold air becase I htested it out with datamaster and when I was sitting the air temps started to rise and I started moving and they quickly went down to around the outside temperature.
Air temperature doesn't vary with velocity. What you are seeing when you were "sitting" is "heat soak" of the IAT sensing element. When you start moving, the air doesn't cool down, but it removes the heat soak from the sensor and the air box.

Other than totally eliminating the inlet duct, its hard to see how you could get more direct than this. (http://cjcfo.fbody.com/members/injuneerzz@aol.com/PhotosB/N2ONozzl.jpg)

injuneer, thats what I meant by once you get moving it allows cooler air to pass through the hood when moving where as when sitting its not and hot air is being sucked in under the hood, I did see a test on ws6.com that showed the maf sensor reading more air flow at higher speeds in different gears with ram air but it wasnt really proportional to the speed so not sure what it proves.
Have to check out your links later some reason the work computer wont allow my to navigate through links....???

What Eric may have alluded to, is that the ram air on a motorcycle has access to 'cleaner' air than full bodied vehicles. This means if the induction system is well designed, IE, a straight path to the TB, but locates the air intake in an area that does not lend itself to high pressure, if won't be an efficient system as a whole. Therefore, the ram effect will not be as effective. AFAIC, like spoilers/wings, most oem ram air placements are designed by stylists, and not engineers. It should be noted, that high pressure translates into low velocity. IOW, you do not want to place the intake opening in a location of high velocity. An excellent reference book would be one authored by Joe Haile, entitled 'Motorcycle Turbocharging, Supercharging & Nitrous Oxide'.

Originally posted by Bud M
I want the intake opening at the location of highest possible air pressure and velocity at the intake....

As I attempted to explain above, it's one or the other. You won't get both at the same location. :) They are opposites.

edit: I just reread your post, Arnie. Now I get it.

As an owner of a 1996 Z28 SS, I believe there is some net advantage to Ram air. Below are some estimates of the effects:

1) On any given Revolution of the engine there is a maximum intake of 175 cubic inches of air consumed (VE=100%)
2) At 60 Miles per hour, the vehicle moves at 1056 inches per second. (5280/60/12)
3) If the opening of the Ram Air is 3 X 8, that is 24 cubic inches of intake potential. (discounting restrictions, etc.)
4) If the vehicle is moving at 60 MPH and the engine RPM is at 1500, then the maximum air intake being pushed through the
plenum is 25,344 cubic inches per second. Wheras the maximum intake is 262,500 cubic inches of air. (<10%)
5) if the vehicle is moving at 60 MPH and the engine RPM is 3000 RPM, then the maximum air intake being pushed through the
plenum is still only 25,344 cubic inches per second. Wheras the maximum intake is 525,000 cubic inches of air. (<4%)
6) The engine does not operate at 100% efficiency, nor does the ram air. In each case, if the VE was low and the
ram air was extremely efficient, then the percentage of ram air would be higher.
7) Conversely, as the RPM rises (I.e lower gears), then the RAM air factor is reduced in relation to the intake demand.


However, this 4-10% ram air effect does offset vacuum that is present when the throttle is light. The effect during acceleration may be enough to generate some additional velocity during the initial foot stomping. In addition, any ram air should increase the velocity inside the intake plenum to some minor degree.

This is not a scientific breakdown and the results are probably even lower than shown. But at 40% VE, light throttle - the ram air may rise upwards of 20% of total air intake.

Originally posted by Bud M
edit: I just reread your post, Arnie. Now I get it.

LOL.. Having read your post, prior to this edit, which noted the addition of the coma for clarification, I then understood where you were coming from. Having recalled your input from previous vehicle aerodynamic discussions, it did strike me odd, that you would state something goofy like that, (prior to understanding your post with the clarification) in this thread. :)

I know this is an old thread, but it's 4 in the morn, and I don't have any thing better to do than read these threads.

IMO C.A.I. pretty much says it all, it's a cold air intake, the delta T across the outside and inside air is the only thing that improves performance.

An airplane with a ram jet engine having the same surface area opening as a TPI 48mm Throttle body will need to reach speeds of >225mph before it will begin to produce any pressure at the exhaust, mind you, it hangs entirely in the air, and is designed to scoop air, so if you really believe your car is ramming air, look up, and make sure you're not strapped to the underside of a 747.

I've been thinking about this one for a few days and I have arrived at this thought: It's not about compressing air at all. A normally aspirated engine has to suck air in and any means of reducing intake manifold vacuum by supplying more air lessens the power loss resulting from the pistons working against intake manifold vacuum as well as increasing the amount of air/fuel mixture in the cylinder.
With that thought in mind I would have to say that the idea of ram air is entirely valid and the only requirement is placement of the ram air intake at a point of high air pressure, and making it large enough to maximize its effectiveness.

Originally posted by arnie
As I attempted to explain above, it's one or the other. You won't get both at the same location. :) They are opposites.

I assume that what you are pointing out is the perpendicular (to velocity) component of pressure, or the the Bernoulli effect. Higher velocity produces lower perpendicular pressure. But it would appear to me that "ram air" effect would be measured using the pressure parallel to the direction of flow, as would be done using a pitot tube.

Originally posted by raul.garcia


IMO C.A.I. pretty much says it all, it's a cold air intake, the delta T across the outside and inside air is the only thing that improves performance.

Cold air is one of the benefits but it is the ramming of air that is largely responsible for increasing power. Before I installed FTRA I had the cold air factory SS hood and the FTRA made a big difference OVER the cold air. That is undesputable evidence ram air works IMO.

Originally posted by Injuneer
I assume that what you are pointing out is the perpendicular (to velocity) component of pressure, or the the Bernoulli effect. Higher velocity produces lower perpendicular pressure. But it would appear to me that "ram air" effect would be measured using the pressure parallel to the direction of flow, as would be done using a pitot tube.

Actually Fred, I was implying pressure measured parallel to the direction of the flow. As you stated, this would appear to be more appropriate for measuring the ram air effect. This (making this more complicated than it should) high pressure/low velocity scenario, as you are aware, has the ram air inlet attached to a vehicle cutting through the air stream, typical of a real/practical situation. IOW, the high velocity air is halted/slowed by the body panel, as well as the ram air opening itself, that is attached to the body panel. If we were to monitor a probe that was far enuf removed from the vehicle body, IOW, in clean undisturbed air flow, also parallel to flow, person might not agree that scenario still applies. But in order to take a measurement, the air flow is again slowed at the probe opening. Agree? I believe I succeeded in making this reply as confusing as possible.

Originally posted by arnie
Actually Fred, I was implying pressure measured parallel to the direction of the flow. As you stated, this would appear to be more appropriate for measuring the ram air effect. This (making this more complicated than it should) high pressure/low velocity scenario, as you are aware, has the ram air inlet attached to a vehicle cutting through the air stream, typical of a real/practical situation. IOW, the high velocity air is halted/slowed by the body panel, as well as the ram air opening itself, that is attached to the body panel. If we were to monitor a probe that was far enuf removed from the vehicle body, IOW, in clean undisturbed air flow, also parallel to flow, person might not agree that scenario still applies. But in order to take a measurement, the air flow is again slowed at the probe opening. Agree? I believe I succeeded in making this reply as confusing as possible.

Not necessarily....as was mentioned before...the velocity can be measured by a pitot tube which, if you've seen one, isn't much of a restriction at all as the size of the tube and the diameter itself is really negligible to the disruption of flow to the intake.

I believe it's 7:30 in the morning and I still haven't slept yet so hopefully my response was not as confusing as possible. ;)

I agree that the whole concept of Ram Air has become more of a "stylists" concept than an engineer's concept. The aerodynamics of the body panels are going to have a lot more affect on the pressure at the air inlet than the simple fact that someone cut a couple slots in the hood - I think that's what Arnie said in much more technical terms????. It really needs to be reviewed for each specific application. Obviously the the hood scoop on the 4th Gen Camaro SS is not as effective as the one on Kurt Johnson's Pro Stock body.

I think people who throw around claims of "CAI is better than ram air" and vice-versa have never taken the time to look at the flow of air around (and under) the body to determine if there is any real benefit of one vs. the other. Might be an interesting "project" for a budding engineering student.... measuring air pressure at the TB for a specific configuration... e.g. LT1 WS6.

First, the ‘ram air’ intakes that we’re talking about don’t make it past the boundary layer of air on the surface of the hood.

Second, what’s better, air 6” from the pavement that is heated >20* over ambient by the sun heating the asphalt, or air taken from 2’ above the pavement pretty close to ambient temp?

My boss (at the engineering firm I work for) told me that cowl induction is better then Ram Air....he drew something on a light pole (we were in a parking lot leaving work)....showed how as air is forced into the "ram air" opening...that something called "packing factors" make it useless....that it doesnt' really "force" air in....and that the only thing you can do is make the air colder for a denser charge....I mean...is the arguement about the "ram" effect or the temperature...

F-body owners who doubt ram air works need to try FTRA. It is one of the best mods I have! The gain is very noticeable OVER cold air which I had previously. The car pulls harder and harder the faster you go. It is well known FTRA is good for 2 miles per hour in the quarter. What more proof do you need! : )

FTRA forces large quantities of pressurized air from the bottom of the car and the LS1 really responds. :thumb:

It is well known FTRA is good for 2 miles per hour in the quarter. What more proof do you need! : )

How much of that is just due to cleaner cold air? You can't use a dyno to prove that, and you can't use ETs because of driver inconsistency...there is no real way to prove it works except a bunch of people spending 150$ and saying it does....when the physics and dynamics behind it says that it doesn't do anything.

Cleaner cold air? Did you read my post? I said I had COLD AIR previously and ram air made a difference OVER cold air.

So basically what you're saying is you don't believe a bunch of people who say FTRA works. Isn't that what these boards are for? To learn from others with real world experiences? It's not like I would come on here and lie. If FTRA didn't help I wouldn't hesitate to blast it just like I did about the SLP MAF which is now sitting in a box.

Yes you are correct...you won't see the gains on the dyno. After installing FTRA I immediately noticed how the car pulled harder and harder the faster you go. It was as if the torque curve became steeper.

Originally posted by Jettison
Cleaner cold air? Did you read my post? I said I had COLD AIR previously and ram air made a difference OVER cold air.

So basically what you're saying is you don't believe a bunch of people who say FTRA works. Isn't that what these boards are for? To learn from others with real world experiences? It's not like I would come on here and lie. If FTRA didn't help I wouldn't hesitate to blast it just like I did about the SLP MAF which is now sitting in a box.

Yes you are correct...you won't see the gains on the dyno. After installing FTRA I immediately noticed how the car pulled harder and harder the faster you go. It was as if the torque curve became steeper.


Are you using your "butt-o-meter" to measure these results or have you quantified them? You mention MPH increases in the 1/4, did those increases come with the same DA, temp, humidity, etc?

Originally posted by Jettison
Cleaner cold air? Did you read my post? I said I had COLD AIR previously and ram air made a difference OVER cold air.

So basically what you're saying is you don't believe a bunch of people who say FTRA works. Isn't that what these boards are for? To learn from others with real world experiences? It's not like I would come on here and lie. If FTRA didn't help I wouldn't hesitate to blast it just like I did about the SLP MAF which is now sitting in a box.

Yes you are correct...you won't see the gains on the dyno. After installing FTRA I immediately noticed how the car pulled harder and harder the faster you go. It was as if the torque curve became steeper.

Take a deep breath...a step back and re-read this entire post. May I suggest reading both of Injuneer's posts and Ultra_Dog's as well.

Congratulations that your butt is telling you that your FTRA has a steeper torque curve than your CAI.....but sorry chap, it just isn't so. You can preach on all you want about your butt-o-meter and what other "people" say about FTRA, that still won't change the facts.

I can convince everyone on this board that the conservation of lateral momentum is totally false but that doesn't make it any less true.

Sorry to burst your bubble :( I would give you a nice big hug right now if I could.

You may want to read this article once more: http://www.vetteguru.com/ramair/ and tell me why your butt should override fluid dynamics.

Ah what the heck...here's another link:

http://www.snowgoercanada.com/tech_ram_air.shtml

Yes...in the end you will get SOME gain but not anything near advertised and the speeds needed for the advertised gain aren't all that practical.

LOL. Yeah I read all that a long time ago, and is why I was skeptical of peoples claims about FTRA. It's interesting how it's only the guys who never tried FTRA say it doesn't work. The fact is the power gain is there even if it is not true "ram air" as per aircraft. Plus it has even been admitted there is -some- benefits such as airbox resonance etc and more available air for the engine (compared to any other induction). If these examples explain the gains and not "ram air" so be it.

I also find amusing how the butt o meter is given zero credibility! Fine, you won't trust YOUR butt but I trust mine, and so do countless others. Plus there is the mentioned improved quarter times. A cold air setup simply is not as effective as a ram air setup. If you only would try it like I did I promise you won't be disappointed. :thumb:

Originally posted by Bud M
It's not about compressing air at all. A normally aspirated engine has to suck air in and any means of reducing intake manifold vacuum by supplying more air lessens the power loss resulting from the pistons working against intake manifold vacuum as well as increasing the amount of air/fuel mixture in the cylinder.

Agreed.:thumb:

The actual "raming" does nothing though, again, any cold air setup with no restriction is as good as any other. Any other setup with no restriction will work just as well.

Besides....I don't think the "constant" ram matters, I was under the impression the engine gulps air in pulses...it doesn't pull x amount of CFM constantly when under constant load at the same RPM. The vacuum statement would be less ram air, and more the intake manifolds volume, I wouldnt' think the pistons would be fighting anything. Again, your losing sight of "ram" air, and unrestrictive cold air. The ram means nothing...

I think we are getting confused by what a 'ram air' system is doing for most of our steet vehicles. Outside air rushes into the air box. This air is much cooler than the air found under the hood, and so yes it improves performance by drawing cooler air into the intake. When speeds start to approach the 100 mph mark, pressuriziong the intake may start to happen, but only at WOT. It may help ram in a little more air into the combustion chamber, but at 100 mph, the pressure increase may be .1-.2 psi at best. At 150 mph I can see it having a beneficial impact on performance as it may start to reach 1 psi. And this is all based on an optomized system. The production ram air system has a few hang ups that wont help it.

Now most cold air induction intakes draw air from under the engine, up front. This air is cooler than what we can find under the hood, so it boosts performance too. BUT when we compare the temps about 6 inches off the pavement on a 70 degree day, which arent much lower than 85-90 degrees due to the heat of friction from tires, to the temps found at the height of the hood where the ram air intakes are, temps will be much more closer to the ambient.
That is the main reason why ram air will perform better than a cold air induction system. It is becasue the ram air gets cooler air than the production intake AND the cold air induction systems most people have, not becasue the intake is being pressurized.

Now, I know I can't prove this to some people, unless I have a test or some hard numbers. But thats what I know. Ram air works great, but not from what the name intends.

Hunter

Originally posted by teamsleep13
Ram air works great, but not from what the name intends.
Hunter

Exactly, it works...but there is almost no pressurizing going on, and none that will have any significant affect on HP. Cold air...thats all you can strive for...but people will continue to spend 100-200$ on "ram air" kits promising 20-30HP gains.....

Originally posted by StealthElephant
Exactly, it works...but there is almost no pressurizing going on, and none that will have any significant affect on HP. Cold air...thats all you can strive for...but people will continue to spend 100-200$ on "ram air" kits promising 20-30HP gains.....
It's a mistake to assume ram air and cold air perform the same IMO. A cold air setup does not lessen intake manifold vacuum like ram air does. The engine benifits from an air blast straight into the otherwise power robbing vacuum.

Much better than a simple cold air setup IMO.

Yes, ram air and cold air dont perform the same....thats definatley true, but I think it is false to say it gets a straight shot into the intake, unless you design it just like that. Most ram air systems have baffles and other obstructions the air must negotiate.
But I will say that at high enough speeds, the intake vacum will lessen when ram air is used, but IMO thats not the reason it will gain you power.

Hunter

Originally posted by Jettison
It's a mistake to assume ram air and cold air perform the same IMO. A cold air setup does not lessen intake manifold vacuum like ram air does. The engine benifits from an air blast straight into the otherwise power robbing vacuum.

Much better than a simple cold air setup IMO.

There is no lessening of the manifold vacuum going on, you NEED vacuum, you don't have enough outside pressure to force air in, the ONLY thing putting air in the cylinder is vacuum...the engine doesn't take in constant air, it takes it in gulps. As stated before, the pressure one of those "ram air" setups could EVER give you is around .1-.2 at 100MPH, which is basically good for nothing, the baffle you put on is causing more aerodynamic drag under the car then any power it could be adding. It's not like with a cowl hood the engine must SUCK air in, and with ram air more air can go in because it's being pushed in as opposed to sucked in. The manifold holds a certain volume of air, the engine then takes in air in gulps. Its not constant, since we have determined that you cannot build any decent pressure the only thing you must do is make sure the intake is always at full volume. Any cold air induction with low restriction will do this.

Think of what it takes a supercharger to make boost, 10-25k RPMS....that is what it takes to FORCE air in, a N/A engine is a vacuum, thats all it is, that vacuum is the only thing making sure air gets in, because god knows that ram air setup with .1 PSI @100MPH isn't doing ANYTHING.

[QUOTE]Originally posted by StealthElephant
[B]"""There is no lessening of the manifold vacuum going on, you NEED vacuum..."""

There certainly is a lessening of vacuum FORCE when there is a wind blast into a vacuum.
Look at it this way. Ram air is comparible to sticking your head out the car window at highway speeds and takeing a deep breathe. Your lungs will fill with air in an instant.

"""The baffle you put on is causing more aerodynamic drag under the car then any power it could be adding."""

There is no aerodynamic drag with FTRA. Air is taken from a portion of the stock air deflector beneath the car.

"""It's not like with a cowl hood the engine must SUCK air in"""

No?? You might want to rethink that. A carb or TB in an open atmosphere must WORK to suck in air...as apposed to ram air.

"""...and with ram air more air can go in because it's being pushed in as opposed to sucked in."""

You are correct. You are beginning to see the light! :)

"""The manifold holds a certain volume of air, the engine then takes in air in gulps. Its not constant, since we have determined that you cannot build any decent pressure the only thing you must do is make sure the intake is always at full volume. Any cold air induction with low restriction will do this."""

Incorrect. A cold air setup hasn't the capibiity to match the air volume of ram air. Every bit of extra air counts.

To sum up my ram air experience...does my and countless others experience mean nothing to you? Having had cold air and switching to ram air (FTRA on an LS1 car) transformed my car into a different animal. I kid you not.

There certainly is a lessening of vacuum FORCE when there is a wind blast into a vacuum. Look at it this way. Ram air is comparible to sticking your head out the car window at highway speeds and takeing a deep breathe. Your lungs will fill with air in an instant.

Heh....thats a terrible comparison, an engine at WOT pulling 5000RPMs wont' be affected. We've already confirmed that the only pressure you could ever get on that kind of system is around .1PSI, and thats at 100MPH. The valve opens/closes so fast, vacuum is pulling air in...there is no "pushing".

Well I have to dissagree with our ram air myth author. Hes wrong for all the right reasons.

The ram air effect does exist at automotive speeds ( it is very weak but it is there).
He is correct in that most of the benefit of "ram air" intakes is actually due to cooler intake air, but that does not make the ram air effect nonexistant. In a poorly designed ram air, ie the head light duct system you will have very little ram air effect. In this case most of the compression occurs infront of the car as the air slows down, and very little occurs inside the duct system itself. In a properly designed system you can recover maybe 75% of the theoretical ram air compression.

Lets take his two key points.

1. Compressable flow vs incompressable flow. Actually that is a simplifying "ASSUMPTION" engineers use to make life easier when they do the calculations. At low speeds air acts very close to being incompressable so for many engineering calculations that effect is simply IGNORED. It is not that it doesn't exist, it simply is such a small effect that for most calculations like wind load on a sky scraper or lift on a wing It has a small effect compared to the primary load being computed and can be ignored.

[edit] for example NACA ( organization which became NASA) did some studies before WWII on maximum ram pressure at low and medium air speeds. At 150 mph the max ram pressure for incomressible flow was .027189 % of atmospheric pressure, for adiabatic compression the gain would be .027454%.

CODE




mph incompressible adiabatic compression
x atm pressure x atm pressure
70 .0059212 .0059338
80 .0077338 .0077553
90 .0097881 .0098223
100 .012084 .012136
110 .014622 .014698
120 .017401 .017509
130 .020422 .020572
140 .023685 .023886






2. Proper duct design. He correctly described a properly designed ram air intake. He described the exact design typically used in F1, and most open wheel racing series, and the design of the tall ram intake scoops popular in drag racing.

The inlet on the scoop setting up over the drivers head in the open wheel cars and on the hood of the drag cars is much smaller than the total opening of the intake at the carburator or throttle butterflies. There is also an expansion plenum behind that small inlet to allow the air to slow and compress to build pressure in the intake.

The following quote is from a Chrysler corporation drag racing reference available in the 1970's
========
"A hood scoop has two basic functions that it must perform. One is to provide cold air to the carburator intake an the other is to have this air forced into the carburetor inlet without restriction.

Any number of scoops or pickups can provide cold air. The important thing with cold air is to seal the scoop or pickup to the carburator inlet.

The forced-air aspect is more difficult. The scoops shown in Figures 16-2, 16-3, 16-4 and 16-5 along with the shaker and air grabber designs will provide forced air to the carburator."
========


The effect is small and is a function of the air density and the square of the speed. It works out to about 3% of static air pressure at 150 mph (.4 psi), so at 75 mph the value would be 1/4 as much or about .1 psi. Doesn't sound like much but under boost the turbo is running at a pressure ratio of about 2:1 so the engine sees a boost of about .2 psi. At 150 mph this becomes .8 psi which is not insignificant. On a 400 hp engine at 14.7 psi boost, this would increase power by about 2.7 % or almost 11 hp at 150 mph if you had a perfect duct. In the real world you'd get about 75% of that or about 8 hp (2 hp at 75 mph).

I agree in principle with his observations that folks expect too much, but to completely dismiss it as non-existant is wrong. If you are scratching for every little 1/2 hp increase in power it is worth looking at.

Larry

Originally posted by StealthElephant
There is no lessening of the manifold vacuum going on, you NEED vacuum, you don't have enough outside pressure to force air in, the ONLY thing putting air in the cylinder is vacuum....It's not like with a cowl hood the engine must SUCK air in, and with ram air more air can go in because it's being pushed in as opposed to sucked in..... a N/A engine is a vacuum, thats all it is, that vacuum is the only thing making sure air gets in...

If what you stated were true, a NA engine at WOT could/or would not function. You don't NEED vacuum. The engine does not SUCK in anything. It is being pushed in by atmospheric pressure, or a pressure differential if less than atmospheric.

Outside air is like 14.7.....a N/A engine is a vacuum....thats all it is.....the exhaust valve opens, air goes out, exhaust clsoes, intake valve opens, piston is at TDC, it drops to BDC, the piston dropping creates vacuum, air must come in via the intake valve to make up the difference.....timing and ignition/overlap etc changes some things...but in general it's a vacuum.

There certainly is a lessening of vacuum FORCE when there is a wind blast into a vacuum.Look at it this way. Ram air is comparible to sticking your head out the car window at highway speeds and takeing a deep breathe. Your lungs will fill with air in an instant.

This is not right. Have you ever stuck your head out teh window and opened your mouth? Air does not rush into your lungs. WHY? Becasue at speeds of 60 mph air doesnt have enough force to force into your lungs.

All of that aside, ram air is a working thing...but only at higher speeds. Like the article says, with a perfect duct, you would gain about 10 hp from ram air at 150 mph.
We dont have perfect ducts, and we are talking bout speeds around 60 to 120 mph.
Gains will happen, but not much
Which brings me back to my original point, the power gain you feel with ram air over a cold air induction kit which is taking air from close to the pavement is from the cooler air that the ram air induction lets the engine breathe.

Now about the engine being a vacum...
Yes a N/A engine uses vacuum to suck in the air fuel mixture. When the valve opens and the piston pulls down, it creates a pressure differential(vacuum) and pulls the air fuel mix into the cylinder. Thats correct right? For the exhaust, the exhaust gets pushed out by the piston. So it is an air pump right? But I wouldn't say the engine is a complete vacum, but it needs it.

Hunter

Guys, Arnie is right. There is no vacuum present in an internal combustion engine intake system. It is a pressure differential. It's only a minor point, but it does help to think correctly about how the engine works if you use the correct terminology. The intake manifold pressure is less than atmospheric pressure, but it's not a vacuum. Since the intake manifold pressure is less than the air pressure outside, the pressure differential PUSHES air in, no suction is involved here.

It "acts" like a vacuum then. If the correct term is pressure diff thats' fine. It's not a vacuum in the purest sense....but either way....it looks like we've established that ram air does almost nothing. I guess it's just a matter of whether or not you consider a 2-5HP gain to be worth 150$.

Vacuum - a space partially exhausted (as to the highest degree possible) by artificial means (as an air pump) c : a degree of rarefaction below atmospheric pressure

The piston drops, this causes the pressure to drop in the cylinder, outside atmospheric pressure is 14.7 I believe, this causes air to rush into the cylinder. I was always told and an engine was a vacuum. Are you talking about air going from the manifold to the cylinder or from the outside into the manifold. I'm not trying to argue with what you've stated I'm just interested in knowing what it actually is.

I'm just wondering....the way I look at it is the pressure drop in the cylinder pretty much creates a vacuum. This creates vacuum in the intake manifold. The intake manifold wants to "suck" air in....what creates the distinction between "sucking" and "pushing". Technically you could argue that the engine is sucking AND that outside air is pushing, cause and effect, you can't have the 1 without the other. I would think that since the engine itself is causing the pressure drop, that the engine is sucking. It just seems odd that if there is no vacuum present in an ICE then why do all carbs work off of vacuum, and why does every MAP EFI system use intake manifold vacuum? There must be vacuum going on SOMEWHERE in the engine if the term is applied everywhere....or is it misused...technically should it be a "pressure differtial" gauge instead of a vacuum gauge....is it the same thign?

My physics teacher always said, there is no such thing as sucking, its all pressure differntial.

But I know where Stealth's head is cause I am thinking the same thing....I guess everone just throws terminology around and it messes us up.
This is what I am thinking:
The piston drops and causes a pressure drop...agreed? This causes a pressure differential and air likes to be at an equilibrium, so air will rush into the clyinder to fill this 'void'. Is that not what a vacuum is?

All this damn terminology is messing me up...I am gonna go pull out my engine theroy books and do some reading.... get back to this tomorrow.

Hunter

Originally posted by StealthElephant
There is no lessening of the manifold vacuum going on, you NEED vacuum, you don't have enough outside pressure to force air in, the ONLY thing putting air in the cylinder is vacuum....

If what you stated were true, a NA engine at WOT could/or would not function. I alluded to this ? in an earlier post. What is the vacuum reading in the intake manifold, on a NA engine, at WOT, with an efficient induction system?

It's not like with a cowl hood the engine must SUCK air in, and with ram air more air can go in because it's being pushed in as opposed to sucked in.

Are you stating the cowl area of vehicles, for which properly matched/designed cowl induction/cowl hood was intended, is not a high pressure area? It's about understanding the areodynamics of the vehicle a person is referring to, that determines where in the airstream a person chooses to position the intake opening, that makes for an effective high/higher pressure air entrance. To blanket a specific area, on the body of ANY vehicle, as being ineffective (or effective), would not be correct. Also, I'm confident those reading this thead understand, the pressure obtained is relative, IOW, it would not be comparible to a FI system. However, as previously stated by another, the correct position of the opening is but a part of the 'equation'. The pressured air entering the ducting, if it must be filtered, will be severely compromised. But again, presure obtained is but relative, and not high pressure per sa. Expect a difference between 'cold air', and the (so called) 'ram air', if properly located. How much? :shrug: My main intent however, is to focus on the ? above.

ouch, a thread about a myth has become all confusing by an even bigger myth! Vacuum. Although in laymans terms the vacuum does 'suck air in', your just describing the effect, not the actual cause.

The word vacuum describes the low pressure side of any pressure differential. It can also mean the total evacuation of air. It doesn't have a strict scientific definition and therefore it gets used in confusing manner.

Vacuum cannot and does not suck. The high pressure side pushes the air in. The only reason air goes into a motor is because the cylinder going down creates an area of lower pressure. The air in our atomosphere is being pulled down by gravity. For every square inch of earths surface area there is a mass of air in the imaginary column above it that results in approxiamately 14.7 lbs of downforce. This external pressure pushes the air into the motor/cylinder.

If this is still confusing, just avoid the word vacuum altogether. It doesn't describe anything that can't be explained in terms of pressure.

Although i don't agree with the way they present space as a vacuum (it's just an empty area), here is a link that may also be relevent.
http://science.howstuffworks.com/question200.htm

maybe all this is being picky, but this is the advanced tech forum :)

-Brent

THANK GOD!!!!!!
Brent that is exactly what I was trying to explain......all these damn terms are screwing us over!!!!

So lets through out the vacuum term....so yes pressure from the atmosphere is pushed into the engine because of a pressure differntial caused by teh faling piston. There its done.

In relation to ram air....I dunno where it all fits in, but I think we have come to the conclusion that ram air will give some power gains, but people still dont agree on WHY we get a performance gain.

Hunter

First off, this thread is great! Lot's of good info here. I don't browse the advanced tech section much because some of the info here is a little overwhelming. Anyway, I would like to present something that jumped out at me after reading Jettison's statements-

I'm sure that you are getting a good gain out of the free ram air mod. When you say FTRA I'm assuming you are talking about the mod that a lot of the LS1 guys do which involves cutting the tray that the induction lid sits on, allowing it to draw air directly from the cavity where the radiator sits behind, or doing something similar to this. However, I don't think the ram air effect is what you are feeling. IMO the stock LS1 induction is pretty restrictive, there is not much area for it to actually "draw" air in as it comes stock. If I remember correctly there is a "slit" about 1/3" tall and maybe 10-12" wide that is where the air has to enter, even if the car is equipped with factory ram air. Well, if you cut a huge hole right under the filter, you are able to draw more air in.

Just a thought.

John

Well FTRA shows much better gains than FRA (free ram air). FTRA (Fast Toys Ram Air) is a high quality kit made from stainless steel and is a true ram air induction system. The only incoming air comes from directly above the plastic air deflector beneath the car (the deflector that sometimes hits steep driveways). The forced air goes through a duct that goes into the SEALED airbox. This system consistently shows 2 mph and .1 in the quarter.

FRA on the other hand is not sealed and shows little or no gains even though the airbox is less restrictive.

BTW both FRA and FTRA work best with a lid.