Ram effect
I dont have the TECHNICAL DATA of Ram Air all I have is real world testing at the track. The cars I have done have all picked up close to 3 mph in the 1/4 mile. Yes these cars all run over 120mph. I also had to add fuel and I personally saw 3 lbs of pressure in my intake with the MAP sensor attached to the manifold directly below the throttle body.
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Originally Posted by MADMAN
...I personally saw 3 lbs of pressure in my intake with the MAP sensor attached to the manifold directly below the throttle body.
The equation for the velocity head (ram) of a fluid is: P = (p x v2)/(288 x g) where in this case, P is psi, p is the density of air, 0.076 lb./cu. ft., v is speed in ft./sec. and g is the acceleration due to gravity, 32.2 ft./sec./sec. so to get three pounds of ram pressure, even with 100% recovery of the velocity head, would require a speed of 350 ft./sec. or 239 MPH. It would also provide a power gain of ~ 22%. (Light aircraft and boat speedometers are pressure gauges calibrated on the basis of this formula.)
(Oops! I put in my $0.0174 before noticing I'd strolled into a hornet's nest, oh well, I'll let it stand now that it's written...)
I think my system was more in the neighborhood of 0.5psi increase, and note that is not 0.5psi on top of BAR, but over what the intake was seeing before.
My power difference was only around 5.6%
I don't know how well that follows what the equation would predict, but that's the raw data from the tests.
My power difference was only around 5.6%
I don't know how well that follows what the equation would predict, but that's the raw data from the tests.
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Joined: Dec 2004
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From: K-W, Ontario
I hate to be the second to question that value, but...3 PSI is a remarkable
gain.
I wonder if the calibration of the MAP sensor was thrown off, or the gauge
had been in error.
Another thought is the original setup was so restrictive, it was creating a higher
pressure in the manifold at wide open throttle, when compared to the new
intake system?
I don't know if this 3 PSI is reference to atmosphere, or relative to the old
system?
gain.
I wonder if the calibration of the MAP sensor was thrown off, or the gauge
had been in error.
Another thought is the original setup was so restrictive, it was creating a higher
pressure in the manifold at wide open throttle, when compared to the new
intake system?
I don't know if this 3 PSI is reference to atmosphere, or relative to the old
system?
Originally Posted by Adrenaline_Z
I hate to be the second to question that value, but...3 PSI is a remarkable
gain.
I wonder if the calibration of the MAP sensor was thrown off, or the gauge
had been in error.
Another thought is the original setup was so restrictive, it was creating a higher
pressure in the manifold at wide open throttle, when compared to the new
intake system?
I don't know if this 3 PSI is reference to atmosphere, or relative to the old
system?
gain.
I wonder if the calibration of the MAP sensor was thrown off, or the gauge
had been in error.
Another thought is the original setup was so restrictive, it was creating a higher
pressure in the manifold at wide open throttle, when compared to the new
intake system?
I don't know if this 3 PSI is reference to atmosphere, or relative to the old
system?
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On The Tree
Joined: Jul 2005
Posts: 158
Likes: 0
From: San Leandro(basically Oakland), CA
Madman, could a Hemholtz chamber in a Ram-Air equipped intake produce more boost or would difference in air intake frequencies only be useful when eliminating the amount of vacuum to take in a certain amount of air?
Sorry if you don't understand what I'm saying.
Sorry if you don't understand what I'm saying.
You lost me on that one. Explain some more!! 
Originally Posted by superGMman
Madman, could a Hemholtz chamber in a Ram-Air equipped intake produce more boost or would difference in air intake frequencies only be useful when eliminating the amount of vacuum to take in a certain amount of air?
Sorry if you don't understand what I'm saying.
Sorry if you don't understand what I'm saying.
Originally Posted by MadBill
Erm...
The equation for the velocity head (ram) of a fluid is: P = (p x v2)/(288 x g) where in this case, P is psi, p is the density of air, 0.076 lb./cu. ft., v is speed in ft./sec. and g is the acceleration due to gravity, 32.2 ft./sec./sec. so to get three pounds of ram pressure, even with 100% recovery of the velocity head, would require a speed of 350 ft./sec. or 239 MPH. It would also provide a power gain of ~ 22%. (Light aircraft and boat speedometers are pressure gauges calibrated on the basis of this formula.)
(Oops! I put in my $0.0174 before noticing I'd strolled into a hornet's nest, oh well, I'll let it stand now that it's written...)
The equation for the velocity head (ram) of a fluid is: P = (p x v2)/(288 x g) where in this case, P is psi, p is the density of air, 0.076 lb./cu. ft., v is speed in ft./sec. and g is the acceleration due to gravity, 32.2 ft./sec./sec. so to get three pounds of ram pressure, even with 100% recovery of the velocity head, would require a speed of 350 ft./sec. or 239 MPH. It would also provide a power gain of ~ 22%. (Light aircraft and boat speedometers are pressure gauges calibrated on the basis of this formula.)
(Oops! I put in my $0.0174 before noticing I'd strolled into a hornet's nest, oh well, I'll let it stand now that it's written...)
A rain gauge with a funnel on top will fill up a whole lot faster than a straight rain gauge, but we all the straight rain gauge gives the only accurate reading.
Now I don't have any formula's to back up what I've written, but I did stay at an Holiday Inn Express last night.
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From the standpoint of stagnation pressure, (the pressure produced by bringing the airflow to a stop), it doesn't make any difference what shape the pressure tube is. Of course to do any good, we need the air to flow into the pipe/tube and then to the engine, thus the shape needs to flow like a typical air bell. A funnel is not a good shape! I have a book by David Vizard showing the flow of various entries and they range from ~ minus 7% for a square edged tube to minus 5.5% for funnel shapes to plus almost 6% for an eliptical radius into a flat plate.
As far as Helmholtz resonance (if I understand your question to Madman), this phenomenon would operate totally independent of any ram air pressure and is very limited in effect when more than four cylinders are being fed by one plenum. (there's good info in that same Vizard book, "How to Build Horsepower Vol. 2")
As far as Helmholtz resonance (if I understand your question to Madman), this phenomenon would operate totally independent of any ram air pressure and is very limited in effect when more than four cylinders are being fed by one plenum. (there's good info in that same Vizard book, "How to Build Horsepower Vol. 2")
Originally Posted by jimmyblue
Here's one angle on it... the SS hood has an inlet area
of about 11 square inches (at least, this is what I
recall from measuring every orifice in the tract one day
in a fit of new-owner enthusiasm). That's 0.076 sq ft.
Traveling 60MPH is 5280 ft/min. That means that the
inlet -encounters- only 400CFM of air, that is all that
would pass through a zero-air-resistance hole at speed.
So don't expect big things from it, at street speeds.
You get her up over 100MPH, maybe it starts to make
up for some suction losses in the front plumbing. Or not.
In fact, if -anyone- with a "ram air" setup can show me
a vehicle log in which MAP exceeds BARO by more than
1kPa, at WOT (a big 1%), I will be impressed.
Of course, to benefit modestly all you need is to bring
air temps down to where they do not mess with the
timing. That's a much easier mark to hit.
of about 11 square inches (at least, this is what I
recall from measuring every orifice in the tract one day
in a fit of new-owner enthusiasm). That's 0.076 sq ft.
Traveling 60MPH is 5280 ft/min. That means that the
inlet -encounters- only 400CFM of air, that is all that
would pass through a zero-air-resistance hole at speed.
So don't expect big things from it, at street speeds.
You get her up over 100MPH, maybe it starts to make
up for some suction losses in the front plumbing. Or not.
In fact, if -anyone- with a "ram air" setup can show me
a vehicle log in which MAP exceeds BARO by more than
1kPa, at WOT (a big 1%), I will be impressed.
Of course, to benefit modestly all you need is to bring
air temps down to where they do not mess with the
timing. That's a much easier mark to hit.
Is that 101kpa ?
6600 rpm clutch dump of death Administrator
Joined: Dec 2001
Posts: 4,983
Likes: 13
From: Texas
There is plenty of racing lore about ram air. The vast majority is simple B.S. Most cars don't see any "ram-air" until well into the triple digits. At street speeds, no effect. That why I and others dispute the claims that you see on the C5 boards about ram-air intakes.
Its not to say that at higher speeds you don't see some ram-air efect. But 99.999% of the cars on this site would never see any benefits from ram air.
Madman messes with some serious cars which have the beans to reach the velocity needed to get some effect.
Most of the gains folks see aren't from ram air, but rather from getting cooler denser air in rather than hotter air from underhood which will cost hp based simply on IAT.
Its not to say that at higher speeds you don't see some ram-air efect. But 99.999% of the cars on this site would never see any benefits from ram air.
Madman messes with some serious cars which have the beans to reach the velocity needed to get some effect.
Most of the gains folks see aren't from ram air, but rather from getting cooler denser air in rather than hotter air from underhood which will cost hp based simply on IAT.
On The Tree
Joined: Jul 2005
Posts: 158
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From: San Leandro(basically Oakland), CA
Originally Posted by MADMAN
You lost me on that one. Explain some more!!
Originally Posted by jamnut
I don't know if this makes any difference, but I do know that a PTO tube on an aircraft is shaped like a point such as > with just a little hole in the tip, the ram air that MadMan uses is a big *** funnel such as <, so IMHO it should grab & force more air than just a regular old pointed tube.
A rain gauge with a funnel on top will fill up a whole lot faster than a straight rain gauge, but we all the straight rain gauge gives the only accurate reading.
Now I don't have any formula's to back up what I've written, but I did stay at an Holiday Inn Express last night.
A rain gauge with a funnel on top will fill up a whole lot faster than a straight rain gauge, but we all the straight rain gauge gives the only accurate reading.
Now I don't have any formula's to back up what I've written, but I did stay at an Holiday Inn Express last night.
Originally Posted by MadBill
Erm...
The equation for the velocity head (ram) of a fluid is: P = (p x v2)/(288 x g) where in this case, P is psi, p is the density of air, 0.076 lb./cu. ft., v is speed in ft./sec. and g is the acceleration due to gravity, 32.2 ft./sec./sec. so to get three pounds of ram pressure, even with 100% recovery of the velocity head, would require a speed of 350 ft./sec. or 239 MPH. It would also provide a power gain of ~ 22%. (Light aircraft and boat speedometers are pressure gauges calibrated on the basis of this formula.)
(Oops! I put in my $0.0174 before noticing I'd strolled into a hornet's nest, oh well, I'll let it stand now that it's written...)
The equation for the velocity head (ram) of a fluid is: P = (p x v2)/(288 x g) where in this case, P is psi, p is the density of air, 0.076 lb./cu. ft., v is speed in ft./sec. and g is the acceleration due to gravity, 32.2 ft./sec./sec. so to get three pounds of ram pressure, even with 100% recovery of the velocity head, would require a speed of 350 ft./sec. or 239 MPH. It would also provide a power gain of ~ 22%. (Light aircraft and boat speedometers are pressure gauges calibrated on the basis of this formula.)
(Oops! I put in my $0.0174 before noticing I'd strolled into a hornet's nest, oh well, I'll let it stand now that it's written...)
Running a manometer for relative pressure between the cabin and the ducted intake through the nose (license plate) of a C5, my results confirm the equations generally. No consideration for resonance was made.
I got no measurable increase at 60MPH and only 6 inches of water at 100mph.
about .25 PSI. But it looks neat.
I also ran temperature transducers throughout the engine compartment, at 20mph it is almost ambient everywhere, there is even air moving under the intake manifold.
So cutting your hood up for more air may be counter productive.
Originally Posted by P Mack
Cool experiment, but you don't know how much cabin pressure is changing with speed.
