I used to be into land-speed-record stuff, and I remember back a couple of years ago, a few of the guys went out on their runs on the salt flats and recorded the so-called "ram air" pressure going into their hood scoop at different mph... the results were not what you'd expect to say the least.

So I did the same test on my basically stock-bodied Neon, and I started in the driver's-side fender where most people mount the end of their CAI. The stock resonator-intake-box was removed from the inner fender. I used a digital industrial +/- psi transducer to get these readings (don't ask where I got it) Here's what I came up with in psi:

0 mph ------ 0.00 psi - idle
30 mph ----- 0.17 psi - 4th gear
40 mph ----- 0.23 psi - 4th gear
50 mph ----- 0.20 psi - 5th gear
60 mph ----- 0.06 psi - 5th gear
70 mph ----- (- 0.14 psi) - 5th gear
80 mph ----- (-0.19 psi) - 5th gear
90 mph ----- (-0.22 psi) - 5th gear

There is obviously cold air getting inside the fender, but right around 60 mph the amount of incoming air from the front bumper can't keep up with the air escaping the bottom of the fender (as well as the air being taken in by the CAI).

I concluded that the negative air pressure at higher speeds was due to a combination of things. The aerodynamics of the front bumper tends to push most of the above, below, and to the sides of the car... not through the bumper. The opening on the bottom of the driver's-side front fender is larger than the opening in the front of the bumper. At higher speeds, the pressure wave coming off the bumper gets forced under the car, and as the air moves around the car, it tends to vacuum the air inside the fender out of the hole in the bottom and take it with it....

So I took a piece of plastic, cut it to the shape of the hole in the bottom of the bumper/fender, and sealed it flat. This way I was hoping the air would come in the front of the bumper and get trapped in the fender where the CAI could gobble it up. Here's what I got (same gearing):

0 mph ------ 0.00 psi (duh)
30 mph ----- 0.22 psi
40 mph ----- 0.27 psi
50 mph ----- 0.30 psi
60 mph ----- 0.32 psi
70 mph ----- 0.34 psi
80 mph ----- 0.36 psi
90 mph ----- 0.37 psi

I suspect that if this test could somehow be done with a Neon at 150 mph (ha ha not my Neon), you'd see it top out around 0.5, and start dropping again after that, but that's a completely different story. Anyway I guess this goes to show that just because a CAI is getting cold air, it doesn't necessarily mean it's getting the most air it can. I took a $0.80 piece of plastic to "seal" the fender on the bottom and improved the air density in the fender substantially, just by cheating the aerodynamics of the car.

This also disproves the 3-or-4 psi gains that people like to throw around about "Ram-air"and scoops and everything else...I don't think so.

 

well i've seen people make theit own "ram air" system on a neon before... all they did was use some sort of extendable pipe and a plastic scoop sort of thing that fit right into the space on the corner of the bumper and had a filter on it as well and there you go... ram air.... how effective it was i cant tell ya but its all good.... im good with my CAI for now... and you should have measured the pressure inside the CAI pipe b/c that would more accuratly give you the reading of how much air it is getting at any given speed instead of how much air is passing into and out of the front fender and fascia, also after you put that plastic piece on the bottom of it did you consider the drag you have now put on the car.. i could bet that you have canceled out how much power you think you have gained due to drag... but thats just a thought b/c instead of the air having somewhere to go it will just fill that compartment and then try to force itself back out the way it came thus defeating the purpose slightly but its all good....i mean those numbers are fairly impressive but they dont tell you how much air is actually inside the CAI piping which is what matters most.... and those negative readings you got in your first test could also be due to the fact that in 5th gear at 70+mph the engine is not reving high enough to need all the air that is passing through the CAI piping... but good results anyway you look at it

 

Interesting testing showing admirable attention to detail.

A link that might be of interest from Australia:

http://autospeed.drive.com.au/cms/A_107824/article.html

 

dat is usefull info

 

ORIGINAL: Izero

after you put that plastic piece on the bottom of it did you consider the drag you have now put on the car..
^^^^I know the stock resonator fills in that gap so it is almost sealed. I mean...if it was hurting the cars performance drag wise they easily could have not done that. Good point though. That is also worth looking into. It might hurt the power...idk

but they dont tell you how much air is actually inside the CAI piping which is what matters most....
^^^^Another good point.

and those negative readings you got in your first test could also be due to the fact that in 5th gear at 70+mph the engine is not reving high enough to need all the air that is passing through the CAI piping... but good results anyway you look at it
^^^^True...maybe. I thought that there was some kind of vacuum suction. If so, does it increase the more the TB is open?

Very interesting info though. Thanks for posting man

 

I'm sure the vacuum would increase at WOT in a lower gear. I doubt that there are many aerodynamic differences between having the plastic in there or not in there... kind of like the myth of driving with your windows down---their is no noticeable difference.

But anyway, the point I was trying to make was that it helped airflow get to the CAI more efficiently... but not drastically like many claim.

 

well actually we did a physics experiment using a few CAD drawings supplied by a few different companies and using computer analysis to figure all of the tough stuff out, and the results we got were that at speeds of 60mph is is actually more efficient to have the AC on than have the windows down, b/c the engine is actually doing more work to overcome the drag put on the car at cruising speeds. and at roughly 160mph if you were to open ONE of the windows you can actually throw the car into a spin which will most likely overcome the friction between the car and the ground and hurl the car into a few flips but hey its all good.

as for that small plastic part i doubt it will have much effect on daily driving but at the track i would think that it could quite possibly cause a difference of a little less than a hundreth of a second, which sometimes can mean the difference in winning or losing in any type of serious competition.....but just for street driving i doubt it will have much of an effect...

and as for the vacuum being greater at WOT, the answer is yes there would be more of a vacuum inside the CAI pipe because the TB is opened more than it would be at anything less than WOT thus the term (Wide Open Throttle) i'd actually love to know how much pressure is inside the pipe at those speeds so if you do another test dont hesitate to post up the results.... but you also might want to include a lower gear at a higher speed...

 

Yeah, I already knew most of that, although I disagree with the 160 mph flip by opening a window... in the real world that would not apply very accurately.

I would have did the vacuum test in the CAI itself, but I didn't feel like drilling and making an extra bung to do so. Maybe if the opportunity presents itself again I will do that, but to be completely honest, I don't really think I'll ever have the time or the reason to pursue this much further than I did. If someone else would like to input more data though, that would be great.

 

Dont know about the 160 mph flip thing but, I can personaly tell you at 160+ mph the drag is terrible and any slight change in anything is extreme. You dont realise it till you go that fast.

 

Yeah, about the only time I went 160mph for a long period of time was in a '85 Mustang GT convertible... unfortunately I was the passenger which made it even more nerve-racking than usual, but anyway yeah the air whipping around the top and the sides was pretty violent.