Cascade Crew

iansane · Posted: Fri Apr 25, 2008 9:13 pm Post subject: Aero Tech?

My car has had the weatherstripping at the back of the hood removed pretty much since I bought it. I've had an issue with some water leaking into the foot wells and since that striping is only $10 I figured why not, couldn't hurt. I popped that back in there and it seemed to help quite a bit.

On my way to work the other day I did a bit of a high speed run (speeding is baaaaaaaad) and noticed that the hood was lifting up quite a bit. Especially across the center. Almost a good quarter inch or so. This seemed to have only come from after putting the weather striping back in. Am I trapping air down under the hood? I also could attribute this to the frame of the hood coming unglued from the sheet metal in a few spots, correct? Also, at the leading edge of the hood there is also a sizable gap between the bumper cover and hood where the cover has "dropped" or something. I need to get under there and try to raise it back up. Is it just caused by the combo of the leading edge of the hood scooping air, the frame separating, and the normal amount of trapped air? Is the "normal" amount of trapped air bad?

Am I just seeing the effects of trapped under hood air moreso with these other problems and it's not that big of a deal or should I look into some aero mods? ala front breather conversion, some sort of larger airdam/splitter or even a vented hood?

/ramble

Dewey316 · Posted: Fri Apr 25, 2008 9:30 pm Post subject:

The issue is a few things, there real issue is the airflow across the top of the hood. Aerodynamics 101 here. High speed air across a surface = low pressure. Low speed/no movment = higher presure.

The only real way to reduce the effect, is to get the air out from under the hood, a front breather conversion won't really do this, unless you vent all the air from the radiatar out the hood (ala - Corvette C5/6 R hoods). You could put some vents on, the stock location of the side vents on the TA hood would help a little. You could also put some louvers behind the radiator in the hood.

The other solution, is to create an undertray IF you do this, you will need leave a 1"-2" gap along the trailing edge for the underhood air to escape, the air flowing along the undertray and then below the car, should create a pressure drop across the trailing edge gap, this will help pull air out. Ideally you would have a full flat undertray on the car, a venting system from the radiator exit, and a couple of NACA ducts to get engine air/heat out. But that is really overdoing it.

I would start by opening up your T/A rear heat vents, those being open should help vent. Some louver/cents behind the readiator (but as far forward as possible on the hood) will also help a LOT. THe lowest pressure on the hood, is very far forward, since the flow seperates and has a turbulant boundry layer the farther back the hood you go, the less low pressure zone there, so you want to vent the hot radiator air at the lowest pressure zone you can, which ends up being as far forward on the hood as possible, but behind the radiator.

You could also do a wicker-bill (small 1/8" 90* edge on the back end of the hood) and then just take off just a bit of the rubber trip on the hood. The wicker-bill will help created more low pressure at the cowl area as it works like a vortex generater, and will energize and accelerate the airflow there, this would really help to suck the air out from under the hood.

Hope that helps

--John

iansane · Posted: Fri Apr 25, 2008 9:38 pm Post subject:

Thanks Dew. I was hoping you'd chime in.

So, something like if I get a hold of a base bird hood and chop a hole right behind the rad? I'm picturing something a little tasteful though, like an inverted scoop facing forward?

I'm trying to visualize what you describe as the wicker-bill. Are you saying a wicker-bill and opening the rear vents? or removing the weatherstriping again and trying to pull it from underneath?

What would a wicker-bill be made of? lexan? stiff rubber type material?

I think the problem with the stock TA vents are they're mounted right next to where the hinges attach if I remember correctly. Which means chopping that area out I'd have to rebrace at least a little with some extra metal somewhere.

Dewey316 · Posted: Fri Apr 25, 2008 9:47 pm Post subject:

The wicker bill is made of sheet-metal or hard rubber, whatever. Yes, it will suck the air out from the cowl area. Think along the lines of a cowl induction, but it sucks the air out, instead of it going in there.

Here is what a wicker bill is.

that pushes the air up and energizes it (think like a spoiler does), because of this, a low pressure zone occures at the base of the windshield (since the fast moving air is pushed up and over the car), and will suck the air out from under the hood, as long as it isn't sealed with weather stripping.

Here is what I am talking about with the vent behind the radiator. This is how the C5-R does it.

That will suck the air out from the radiator, and it also doesn't allow that air to collect under the hood, created the high-pressure zone. To really make that work though, you also want to do an undertray to help get the air out form the engine compartment. the wickerbill will help, but it will just also suck up air from under the car, so you really have attack that also.

iansane · Posted: Fri Apr 25, 2008 9:50 pm Post subject:

I wonder how much room I'd have to go down like that? Have you seen a thirdgen (bird or maro) with a hood like that custom or otherwise?

Dewey316 · Posted: Fri Apr 25, 2008 9:53 pm Post subject:

nope, the closest I have seen is the japanees camaro. Without converting to a front breather, this gets a little more complicated. You would need to undertray from the air-dam back, but you can't go in front of the air dam, because you have to get air to the radiator. Then something on the top of the hood, to help vent air, and a wicker-bill would help.

You might consider just getting some generic louvers, and put them where the scoop would be, that big of a scoop really isn't all the practicle, but louvers there would help vent the air out, the wicker-bill would also help vent the air, T/A heat extractors would help vent the air, and the undertray would keep air from flowing in from underneath, and also help vent. You will probably still get some lift from the hood, but all those things would help minimize its effects.

iansane · Posted: Fri Apr 25, 2008 9:59 pm Post subject:

Would it be detrimental to just work from back to front? As far as the hood goes. Start with the wickerbill, maybe trying different heights/angles? Then louvers/vent at front and rear of the hood and after that the undertray/front breather issue? Being a driver restricts what I can do with this at one time.

Dewey316 · Posted: Fri Apr 25, 2008 10:02 pm Post subject:

I would start with the undertray, then do the wicker-bill, then do the extractors.

See, you can do louvers/vents something like the Mecham stuff too.

The key is just getting the air out from under the hood, but the first peice to that is really the undertray, otherwise the air just flows in from under the car, and you get no where.

iansane · Posted: Fri Apr 25, 2008 10:35 pm Post subject:

Hrmm.... Sweet. This'll give me something to dream about doing when I never have a second off work/school. Thanks John! Laughing

Dewey316 · Posted: Fri Apr 25, 2008 10:38 pm Post subject:

Yeah, most of the stuff is somewhere on my very long list of things I am "going to do one of these days"

STEEL · Posted: Fri Apr 25, 2008 11:04 pm Post subject:

Sounds to me like you need a two inch cowl on there....

Dewey316 · Posted: Fri Apr 25, 2008 11:16 pm Post subject:

No, a cowl won't help, unless you delfect the airflow, a cowl would have the opposite effect, without the wicker bill, you have a high pressure zone at the base of the windshield. With just a cowl, you make the problem worse.