Here in Europe,these things are marketed as AIRPOWER.They simply increase the air turbulence before it reaches the inlet manifold.It strangles the air at low revs giving you an illusion that as you step on the gas you get more power!!!!!!This is only so because it strangles it in the first place!!!!After all, if your air-filter is dirty doesnt your car feel slower???
On Turbo-intercooler cars(like my 3.0D) they recommend fitting 2 of these,one before the intercooler(after the air-filter) and another after the intercooler(near the inlet manifold).A friend of mine installed this on a Golf Tdi-150 (against my better judgement!) and lost max boost pressure,and gained more black smoke(proving that the Airpower restricts the air-flow mass!) .He asked for his money back!Each Airpower here costs about 90 Usd!!!!!!!(no wonder they recommend 2!!!!!)Now for some quick effective DIY power gain tip!Try drilling a 2.0" hole in your airbox!I got more boost pressure at lower Rpm,but mine is a Turbo Diesel!On a 3.0-4.8 ,the air-intake sound will bring a smile to your face..........

This mod was quite common on a Toyota Board that i belong to. Deckplate Mod

Are you saying that this thing is milled from a solid piece of aluminum? Can you post a pic? I'm curious about what it looks like. I had assumed the vanes are just folded over sheet metal and riveted or soldered. It's the rivets or solder that I was referring to as potential shrapnel.

It works on all cars.You will see more gains if your airbox is restrictive!We saw a power gain on a Fiat 2.0 Coupe Turbo of 15 bhp!!!!!thats just with the ECU adjusting by itself!No fine tuning involved!

this is the Airpower I have been referring to.........

Ah, that's what I had in mind. A sheet metal ring with 6 smaller pieces of sheet metal attached inside for vanes. All held together by ?

Go to thread...vote for my next mod by ROC3b
 

It is posted there, for some reason you cannot post the same pic twice here. I even renamed it.

http://www.xoutpost.com/attachment.php?attachmentid=1929That one looks quite different. I see what you mean about it being one piece. I'd venture to guess that the cross sectional area open to flow is about half of the intake opening. That's gotta produce a pressure drop.

That might be where this one is different. If you look close at this picture the inside of the peice it is flat. I ran the shop vac in reverse to see if I could see something or feel somthing in my hand...I did not notice any drop off and in the tub it fits flat agianst the inside of the tube.

If you folded the vanes back up it would be just short cylindrical piece of tubing. With a short length of round ducting I could make one of those in 15 minutes. Then I could rig up a test to measure the pressure drop using your shop vac idea. Might be a fun science project.

Have you thought about using some smoke in combination with the shop vac to see if it creates a vortex? You really need to put the thing in a section of tube for a proper test though. The boundary effects are significant for creating the vortex.