is ram air real?

[SkifDank]

I'm the owner of an '87 firebird and was getting info on various intake systems when I came across this guys site.. I'm not sure if anyone is familiar with this guy or his page but can someone please tell me whether or not he knows what the h*** he's talking about??
you guys know alot more than I do but I think this guy is just trying to sound scientific (he even throws newtons law in there) and indepth, but seems rather confused about basic concepts.

http://www.gemair.com/~phorine/Artic...ir%20Myth.html

Thank you.

[Backfire]

Having just skimmed that page, it seems like most of the individual facts he presents are correct. But I am not sure on the sum of the parts. The relation between air velocity and pressure is correct. And his point about needing to slow the air to increase the pressure is correct as well. I had always assumed the point of the ram air scoops was to put the inlet in a high pressure region.

When an airfoil (airplane wing) is traveling through a fluid (such as air), there is a point on the surface of the airfoil called the stagnation point. This is where the velocity of air is assumed to be 0 and pressure is greatest. The stagnation point is generally on the leading edge of the airfoil. As the air passed on top of and below the airfoil the velocity increases. The path of the airflow on top of the airfoil is "longer" than the bottom, therefore the air must travel faster on top of the airfoil than on the bottom. Since the velocity of the air on top of the airfoil is greater than on the bottom, the pressure on top of the airfoil is less than the pressure on the bottom of the airfoil. Since pressure is a force distributed over an area, the greater pressure on the bottom means the air under the airfoil pushes up more than the air on top pushes down. This pressure difference is what provides lift to the airfoil.

So how does that apply to cars??? Without any testing, its hard to say. But just by looking at it, the positioning of ram air scoops like the SS and WS6 seem like they would be more closely related to the top of the wing than the stagnation point. Meaning the velocity is going to increase and the pressure will drop compared to atmospheric conditions. My guess is that at typical speeds, the differences in pressure are not drastic enough to make a noticable performance difference. When you look at a dragster with the butterfly thottle plates, you will probably see the difference. You are looking at speeds in excess of 200mph. And with the positioning of the butterflies, the air may actually slow down at their face, causing a pressure increase.

If someone with a ram-air hood had access to a couple manometers and some small diameter tubing, you could run a few experiments to test the pressure at the different locations and see if you benefit from the scoop. That would be the best way to set this straight.

[ August 02, 2002: Message edited by: Backfire ]</p>

[Dojo2000]

<blockquote>quote:</font><hr>In plain English, a car is just too slow for ram air to work.
<hr></blockquote>Sums up everything on that site and what Backfire said above.

In the past its been said for ram air systems that 100 MPH = ~1 PSI boost

I've never believed that "ram air" system ever created a "pressurizing" effect in the intake. But I do believe that a "ram air" intake system is much more free-flowing than stock intake sitting in the middle of the engine bay. It seems to me that in a ram air system air is more readily available for the engine to inhale. When your cruising down the road in your WS6 Trans Am more of the air being sucked into your engine is being replaced by air rushing into the intake than when your cruising in your 93-97 f-body with the air box sucking air from your wheel well(and hot engine bay). Kind of a crappy description/comparision but you get the picture.

[ August 02, 2002: Message edited by: Dojo2000 ]</p>

[Arctc Wolf]

Hook up a boost gauge to your engine and put on the ram air kit. see if the intake makes the needle go towards zero. if it does, the ram air kit helps, if not, it's a bunch of crap.

[93v6firebird]

one of the ways Acura gets an extra 40hp into the TL Type S from teh regular TL is w/ an effective ram air system, at least thats what the salesman told me when I asked how the hell they got 40hp more w/ the same engine and why was it I couldnt do that for a lot less than 3000 bucks?

[nova]

<blockquote>quote:</font><hr>Originally posted by Backfire:
The path of the airflow on top of the airfoil is "longer" than the bottom, therefore the air must travel faster on top of the airfoil than on the bottom.<hr></blockquote>

Absolutely correct except for this part.

This situation does not exist very often in an airfoil. Generally when this situation exists the aircraft is in a condition of stall because the speed differential and therefore the pressure differential is very miniscule.

Also the fact is that many airfoils are actually simmetrical between the top and the bottom so the top path and bottom path are exactly the same.

The velocity differentials between airflow over the top of the wing and airflow below the wing are affected by many different variables including angle of attack and various frictional interactions between the fluid and the surface of the wing which are not entirely understood.

Trust me, I'm an aerospace engineer in training. [img]smile.gif[/img]

[2001 Green machine]

Look at it like this-- Take your shop vac , put any nozzle you want on it , get a long extension cord, hold the nozzle in front of you, turn it on and run....Think real hard.... Are you getting any more air into the shop vac because your running?

I agree with Dojo, it's merely a more free flowing system.