ram air a myth?
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Joined: Aug 2001
Posts: 19
From: Long Island NY
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.
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.
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Joined: Aug 2001
Posts: 19
From: Long Island NY
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.
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.
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Joined: Sep 2002
Posts: 672
From: New Jersey
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...
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...
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Joined: May 2002
Posts: 199
From: Seattle Area
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
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
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Joined: Sep 2002
Posts: 672
From: New Jersey
Originally posted by teamsleep13
Ram air works great, but not from what the name intends.
Hunter
Ram air works great, but not from what the name intends.
Hunter
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Joined: Aug 2001
Posts: 19
From: Long Island NY
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.....
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.....
Much better than a simple cold air setup IMO.
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Joined: May 2002
Posts: 199
From: Seattle Area
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
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
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Joined: Sep 2002
Posts: 672
From: New Jersey
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.
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.
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.
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Joined: Aug 2001
Posts: 19
From: Long Island NY
[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.
[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.
Last edited by Jettison; Sep 20, 2003 at 06:01 PM.
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Joined: Sep 2002
Posts: 672
From: New Jersey
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.
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
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
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Posts: 1,462
From: smog zone adjacent to a great lake
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...
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...
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Joined: Sep 2002
Posts: 672
From: New Jersey
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.
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Joined: May 2002
Posts: 199
From: Seattle Area
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.
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
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Joined: Jul 2001
Posts: 727
From: Wolverine Lake, MI
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.
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Posts: 672
From: New Jersey
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$.