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.

 

What is your (Madman) ram setup like?

 

You havent seen it? Search BIG GULP its a crazy setup non the less..

 

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...)

 

Be careful, trying to dispute Madman with math and logic will get you locked in your room with all the furniture in your house piled up against your door...

 

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.

 

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?

 

I cant argue on equations. I do know that the FAST data log showed pressure not vacuum. I was using the MAP reading to add fuel based on pressure. Now this was with the t/b sealed completely to the RAM Air. I had to keep cutting the inlet hole bigger till I got a pressure reading instead of vacuum.

 

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.

 

You lost me on that one. Explain some more!!

 

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.

 

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")

 

Is that 101kpa ?

 

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.

 

Actually what I was trying to say is explained in 300bhp/ton's long post that talks about funtional ram air. I was trying to explain if the altering of the frequency of the air charge would change things.

 

You mean pitot tube? The rain guage with a funnel doesn't act the same way air would. More air doesn't get rammed in just cause the opening is bigger. Only so much air will flow through the opening based on the demands of the engine, any extra will just spill over. You can't fool the air into the funnel by driving into it, the air will get out of the way.

 

I ran a very simple test to confirm what is very well modeled mathematically here.

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.

 

Cool experiment, but you don't know how much cabin pressure is changing with speed.

 

I logged the MAF at WOT with and without the ducting, I saw no meaningful difference.

 

Interesting thread. We were discussing similar context in the Corvette forum. I linked the guys over to this thread.