aero-mods,installment#9(internal drag)

[Otto]

Originally Posted by holypaulie

...
CONS
- more cutting
- require ducting
- require holes for hinges
- less airflow at low speed or traffic
How to mount those hinges to the flap without drilling a holes? How to prevent flap falling inside (down) ?

Epoxy or JB Weld is your friend: no holes to drill. Ducting via Coroplast and duct tape, or aluminum foil tape. With push-pull cable (from bike shop) adjust cowl flap angle. Add (with JB Weld) small lip to keep flap from falling down. Cut one more slot beyond the 3 you were already gonna cut.

How to cut? Dremmel tool? Laser? Router? Hi pressure water jet? This would require a practice run on a scrap piece of metal, using tape to protect the paint surface. Properly done, you would only need to use touch up paint to color and protect the edges after the cut, to prevent rust on the exposed metal edges. Probably best to remove the part from the car and do the work on a bench. Probably worthwhile to ask somebody who does custom body work for input, or artist who works in sheet metal. Probably best to position the hinge on the cut line before making the cut, to make sure all is in perfect alignment after the cut.

[holypaulie]

Thank you very much for details Otto. Your plan require good skills, a lot of work and spent some money. Too much hustle more me, though. I don't know if is worth it.

[Xringer]

Those cuts across the support members look like they will take away a lot of the strength of the hood.
It might actually bend the hood if someone slammed it shut too hard.

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That looks like a screen mesh inside the vent. If it is, surface turbulence on the mesh might restrict air flow. I would try it first, without the screen.

Those are observations of a novice. Likely to be wrong.

Cheers,
Rich

[holypaulie]

Today I have checked my underhood and I can tell there is not much room. On the left side is air intake resonator, on right is air conditioning pipe. Maximum width that I can make a cut and bent it down freely is about licence plate width. I marked on pix where bent would be. Is that enough for efficient working vent ???

[Xringer]

How about installing a cowl induction scoop? (it's like a backwards air scoop).


Might even be able to mount it so it keeps out the rain..

[holypaulie]

Originally Posted by Xringer

How about installing a cowl induction scoop? (it's like a backwards air scoop).


Might even be able to mount it so it keeps out the rain..

I wonder how they would effect aero drag. I guess more front area.

[Xringer]

I'm not sure. Since it's sitting in front of the windshield, does it really add to the frontal area?

The main selling point is, these things don't intrude down into the engine compartment
and I think (at speed) they may actually suck air out.

It would be nice, if one could use the intake and hood-hole size to balance the amount of air flowing out of the vent, so it matched the speed of the air flowing around the outside of the cowling..

[MechEngVT]

Cowl hood scoops are supposed to provide pressurized air to the carburetor inlet at highway speed. The transition between the flat hood and the rather vertical windshield of old muscle cars created a very high air pressure at speed, and the cowl scoop took advantage of this to provide a "cold air" intake with a little extra pressure on it. These do not work well to vent hot air at highway speed.

I have seen pictures of tri-5 shoeboxes run at the Silver State classic road rally with tons of aero tricks to try to keep the front wheels on the ground above 100 mph. Some of those folks cut a wooden block for each rear corner of the hood that's about 3/4-1" high and slam the hood on them. The raised rear corners of the hood bleed off underhood pressure as they are further from the stagnation point in the center of the windshield and the gap runs parallel to the air flow. Placing a side- or rear-facing outlet near the windshield will have to be done with care, and probably by moving it far toward the sides of the car.

[Xringer]

The cowl induction 'scoops' (Output vents?) I've seen on the web look pretty low profile.


If I were to install one on my CRV, I would place it close to the nose,
in order to suck the air out of the area behind the radiator.
The one in this picture seems to be too far back.

Rain isn't going to be able to get directly to the engine, and if you made a small rim around the hood hole and drilled some small drain holes in the cowl, that would drain off any water that ran inside the output vent..

[aerohead]

About 60% of the fuels energy,at any given load, is lost to waste heat.About half of that heat goes out the tailpipe,the other half into the cooling system.As to how much can go back into the inlet tract,I don't have a clue.Charge density would suffer at some point,with power falling off.The PNGV cars were moving the heat exchangers to the rear quarter-panels,ala Ford Probe concepts.As to the "pointy" nose,the body of research suggests we can do as good with less radical architecture.