do ventilation intakes add to drag?
 

i'm talking about the vents in front of the windshield.

my reason for asking as that i recently noticed on my car the intakes are in an odd location. the car's hood kicks up a bit near the windsield and thus forms a bit of a recess where the wipers sit = good. however the actual intakes are locates at the outer edges near the a pillars, and the plastic covers actually show these intakes being ducted to the center where the ventilation fan motor is.

this seems a bit odd as i would assume that the high pressure bubble is strongest at the center/base of the windshield and not near the sides at the A-pillars where the air accelerates to move around the car. Also the fact that the intakes and ducts are the same piece of plastic, just changing the locations of the holes would do the job (and drilling or cutting holes would still do).

why this bothers me is that i have to run the fan most of the time to get some air in the car while my previous car had the intakes where i think they should be, and ventilation was much better.

any thoughts on this?

Does the car have pollen filters and if so have they been changed when they should ?

Same here: ventilation intakes on the sides, hidden under the hood. No air without fan:(
I think moving it to the center won't help much since it'll still be under the trailing edge of the hood which helps hide the wipers.
I think there are only two ways to get forced air into the cabin: either a duct from the high-pressure bubble ahead of the car, or air scoops a la Peugeot 206. Though my Dad-in-law had a P206 and I remember that the fan also had to be on all the time.

As far as i know it has no such filter, it's an older car originally designed in 1988 and mines a 1995 model when the line ended but basically not much changed. It could be the ventilation is more restrictive internally than my previous car... that was a 1985 opel kadett and after it was parked under a tree for quite a while bits of leaf would blow out of the vents :D None of that on this car fortunately, so perhaps there is some sort of filter internally. The fan looks like some kind of hamster wheel so that should make for some restriction too when it's not turning... Still when you design a more restrictive ventilation system wouldn't it be logic to try and tap into the ram effect even more to compensate?

some previous mercedes models and some other cars i've seen have a grill in the hood just ahead of the windshield before the wiper recess that if i recall correct is ducted to the ventilation.

maybe with modern climate controle and filters natural airflow has become less important, but since i'm running the fan a lot i'm looking for ways to reduce my electrical load (as long as that dousn't bring any new drag)

Had one myself. Same problem. I tried to resolve it by removing part of the ductwork under the scoops. I think it was to help keep rain out of the pollen filter but i tried it anyway. Definitely helped airflow into the cabin but it was a bit noisy and kind of howled as i got up to motorway speeds.

ollie

I think that biggest reason why we need more fan, is that air can't find its way to out.

Old VW beatle was dense like mordern cars. (Beatle could float on the water pretty long time) Heater couldn't blow the air from back of the car to cabin. It was needed to add also air outlet to back of the car. I think that same thing would help with modern cars. Easy way to test this theory is to open window littlebit and you get much bigger flow.

Beatle also needet thermal insulation to inflowline to get cabin warmer.

I think that you can't get measureable gains to FE by changing the intake place. Outlet place is more importan. Same thing with cd: You can get more gains from back off the car than from front.

This is just my point of wiev. :)

Modern cars just aren't designed to flow air that way through the cowl, that's what they designed A/C for. 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. New cars aren't designed to take advantage of this now days, and I'd asume the recessed cowl vents under the hood have a large part of this too.

One thing I noticed was that as I added aeromods to reduce my car's Cd, the non fan assisted air flow also got progressively less as I reduced the front high pressure/rear low pressure differential that drives air flow through the vents in most cars. So, in an ultra-low Cd car, is it more efficient to run the vent's electric fan (with its attendant alternator load) to provide cabin ventilation or is it better to accept the added drag of a vent scoop on the hood or windshield to move air through the cabin.

I used to own a 1968 Volvo 144. That car had the air intake in the center at the base of the hood. The air flowed around a baffle, down over the blower motor, and down through the heater core. When parked, snow would find its way into the motor and onto the heater core. The motor was an open motor, with the bearings and windings directly exposed to the snow.

When the engine started to warm up, the snow would melt, and the defroster was a window fogger until the heater core dried out. And the moisture destroyed the blower motor. And it was an eight hour job to replace the motor.

I finally got tired of the problems, so removed the heater blower, sealed the cowl opening, made a fiberglass duct from the cowl through the engine compartment, and installed a GM heater blower in front of the radiator. The heater blower had the inlet facing to the rear.

Since the heater blower inlet was in a high pressure area, I did not need to run the blower at highway speeds. Since the blower was far away, I could not hear it on low, and could barely hear anything on high. And zero problems with rain or snow.

Sometimes, I'm tempted to do something similar to my Canyon to reduce electrical load.

cowl vent
 

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.

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

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:

http://www.wolfsburgwarehouse.com/BD374ab.jpg

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

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.

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.

http://www.oldbug.com/125%20074.jpg
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.

Civic
 

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.