do ventilation intakes add to drag?

[aerohead]

Hucho devotes a whole chapter to HVAC.
Systems are designed for use as basjoos has described.
Ram affects aren't part of the equation.They're looking for a constant pressure differential across the entire speed range.
Make sure your HVAC extractor vent gravity damper is free to move.You may have to remove the rear bumper fascia to get at it.

[Gasoline Fumes]

I also have no airflow in the '91 Civic Wagon without the fan on. My HVAC intake is in the middle.

[freebeard]

JRMichler's mod sounds interesting. Don't forget to bellmouth the duct ends.

In my case the the vent is in the back of the hood in the center, facing straight up where it collects pine needles. With an internal fan and flow-through vents it's still a joke. What works is flipping the wind wings clear around so I get a face full of air and bugs at highway speed. Your car obviously isn't so equipped, so Google [vw] bee-catchers:



Make your own — put them in in the summer and take them out in the winter.

[basjoos]

The Schloerwagen has some interesting cabin vents installed in it. There is a little door scoop that pops open in the front just below the front windshield that lets air in. The other front air inlets are opened by warping inward the upper front corners of the two front side windows (next to the "A" pillars). I'm guessing these exhaust air from the top of the cabin. On the rear side windows, the upper front corners (next to the "C" pillars) are warped inward to allow air to escape from the back of the cabin. The glazing material was probably plexiglass (invented in the 1930's) as it is obviously flexible enough to be custom curved to match the shape of the car and to allow the corners to be bent inward an inch or two for venting purposes. Since this car was designed to be ultra low drag, I would expect the same care to have gone into designing the ventilation system to make its operation as low drag as possible.

If you look at the photo of the Schloerwagen with the propeller mounted in back, you can see it with all of these vents wide open. If you look at the photo showing the interior from the passenger's side door, you can see the clamps that warp open the upper corners of the front side windows. I suspect that downward facing handle just under the dash opens the front scoop vent.

[Sven7]

Originally Posted by texanidiot25

My '69 Chevy has vents in the kicker panels that open up to circulate air low in the cab, as well as through the vents, and the vent windows which move awesome amounts of air.

My '65 Ford truck has these foot vents too. They are unbelievable compared to a modern car! I noticed that with no door speakers, my Civic also gets drafts in a similar area during high winds. I seriously thought about adding real vents down there, with an outlet at the rear of the car in the spare tire well or hatch. I imagine with a couple small NACA inlets in the very front of the doors and short ducts through the door cards, one could have really well (passively) ventilated car.

This would be more for comfort than efficiency because the Civic's ventilation sucks. Remember that every time your car moves air, whether around the outside or through the inside (with the fan off), it's creating drag. Maybe the foot vent method could be adapted, modernized and tweaked for efficiency, because it is a really great way to stay cool.

[freebeard]

http://www.oldbug.com/gates.htm

VW called them 'crotch coolers'. They went away with the introduction of opening wind wings. That page is awesome if you want to see a highly detailed show-winning Bug.

[aerohead]

Originally Posted by Sven7

My '65 Ford truck has these foot vents too. They are unbelievable compared to a modern car! I noticed that with no door speakers, my Civic also gets drafts in a similar area during high winds. I seriously thought about adding real vents down there, with an outlet at the rear of the car in the spare tire well or hatch. I imagine with a couple small NACA inlets in the very front of the doors and short ducts through the door cards, one could have really well (passively) ventilated car.

This would be more for comfort than efficiency because the Civic's ventilation sucks. Remember that every time your car moves air, whether around the outside or through the inside (with the fan off), it's creating drag. Maybe the foot vent method could be adapted, modernized and tweaked for efficiency, because it is a really great way to stay cool.

With modern cars,EPA certification dynamometer loading presumes a drag coefficient with windows rolled up.Many automakers claim less mpg with windows down-ventilation vs windows-up air conditioning.
Honda's design may presume that you'll just use the air conditioner.
In the development of the GM Precept,cabin ventilation,as part of the total "features drag" hardly showed on the wind tunnel load cells.I personally don't believe it's something worth fussing over unless you're out to set a land speed record.