ZBRA

Vehicle: C4 track car with no side windows.

Is the rear cargo area becoming a parachute? All the air coming in through the side windows has no where to go. Solution #1 would be a lexan back window with built in louvers like the old Ferrari F40:



Since no one makes this, and I sure don't have the fabrication skills to do it myself, I have another idea: exhaust for the interior. I'm thinking of running large air hoses from the back wall of the rear speaker holes, around behind the gas tank, and out the back bumper where the license plate opening is.

The speaker holes are the fartherst rear part of the interior. Obviously I do not have speakers or speaker plates in the car.

What do you think?

FastZR1

If your worried about it, just install one of those $15 vent masters that leaves the back window open about 2 inches. The air should go right out the back.

vetracer

I cut the weatherstrip out along the bottom of the rearmost part of the window. I was thinking about adding deflectors to the "A" pillars to keep the air out in the first place...

John Shiels

not much air comes in the car when the windows are open. Like a pickup truck the air in the bow becomes almost stagnant. It doesn't move. That's why when you put a net in the back it instead of a tailgate it is less efficient as the air flow through the net and then it flows over the sides to refill it. That is why a car like LGM's has NACA ducts to pull air in for cooling the driver in front of the window near the A pillar.

Bill Dearborn

The inside air swirls around the driver and seats but doesn't move around much behind that. I have actually had pieces of paper blow out of my closed center console due to the swirling air between the seats and you can hear it buffeting the microphone in my camcorder mounted to the roll bar but paper in the back doesn't move around much. If you open up the back window you will have air flow through the cabin but it will increase drag. If I remember correctly the F40 holes were for engine cooling.

Bill

fatbillybob

I have found nowhere does anyone talk about this. Some 911 guys run rear lexan windows with holes. The F40 holes are for engine cooling only. there is back glass behiind the driver. I do not know what a nascar does to deal with this problem. A car must be more aerodynamic with windows up so the windows down must be doing something negative. Whether venting will encourage drag is something I had not thought about. There seems to be no consensus on open window issues like there is with front spltters and spoliers and wings.

Slalom4me

Monitor for Carbon Monoxide poisoning.

Tasteless, odorless, colorless gas "blocks the absorption of oxygen into
the bloodstream from the lungs, and poisons the red blood cells so they
cannot carry oxygen. If body tissues do not receive a constant supply
of oxygen, they stop functioning. The brain is extremely vulnerable to
oxygen deprivation. Most of the early symptoms of CO poisoning are
the result of brain malfunction from the lack of oxygen."

Anytime I was in a station wagon or similar vehicle with an opening
from the cabin area to the rear of the vehicle, the smell of exhaust
fumes was usually present.

.

chuntington101

while your ducting all that air out the back of the car, you could mount the rad in the back with some nice big fans behind it. then you can run a rear rad setup!

shifts weight to the back of the car and menas you need less opening in the front, or you can duct more to the intake!

thanks Chris.

Solofast

REALLY BAD IDEA!!!!

1. The air at the side window is at a lower pressure and as others have noted, you will suck air (along with exhaust gas ) from the rear of the car into the passenger compartment.

2. If you want lower drag, just make sure that the air at the "B" pillar smoothly reattaches as it leaves the window area. Look at NASCAR windows, the "B" pillar is rounded to allow the flow to reattach. You can do pretty much the same thing with roll bar foam so that it makes the "B" pillar rounded. As a result there will be no "parachute" effect and you will have lower drag. The lowest drag results from moving the air smoothly around the car. The more air you induce into the inside of the car the more drag you create. Partially opening the rear backlite is going to create more drag by pulling air into the car, and then trying to reaccelerate it later....

99BlackZ51

With your side windows open you will immediately create a high pressure air pocket in the rear interior of the car. As soon as this happens no more air will enter the car since the air inside is at a higher pressure than the air outside, same as pickup truck beds. Venting would eliminate the high pressure pocket and create a lot of air flow through the car creating drag as mentioned.

The high pressure pocket under the hood of the C5 is a different story since it creates lift over 150 mph, which is obviously bad, and with the right venting you can turn it into usable downforce -look at the C5R's hood.

Scott

John Shiels

my wheelwells vent out through the hood.

ZBRA

Glad I asked before cutting holes.

parkerracing

For 2006 SCCA allowed roof vents in GT-1 (not sure about other classes). This lowered interior temps by 25-30 degrees (since heat fatigue is a major source of brain fade late in an event, this is a major safety improvement).
One area of concern is when using hood louvers. The air coming in the side windows would bring in all the debris flung out of the hood louvers (typically mounted over the wheels in a GT car).
I solved the problem with filters from a stove range top vent.
Sorry, I couldn't find a good pic.

vstol

The earlier C2's had the vent behind the drivers side which I thought was there for the same reason that ZBRA started the thread. I realize it was 40 yrs ago but were they on the right track?

BrianCunningham

The rear glass on tunnel back 68-7? use to come out. This was to suck air into the passenger compartment and out the windows giving the car better aerodynamics.

I have a photo of one in a wind tunnel.

vstol

Any chance of posting the picture? I’m contemplating on whether or not I need to put one back into my 64 Grand Sport before I finish the interior. It would be rear exit and I have side exhaust. It will see the track a few times a year. Thoughts?

parkerracing

See if this works

http://www.gt1da.com/board/index.php?showtopic=3366

vstol

Thanks for the site I was thinking of internally setting up a vent and exiting out the back.

fatbillybob

Assuming this is true can you help floww or flow separation with gurney flaps on the leading edge of the open front window just like is done on the leading edge of a wheel well? Kinda like this only picture I have.

Solofast

If the objective was to get more air out of the inside of the car, the short answer is yes, you could get more air out of the inside of the car putting a lip on the A pillar. Problem is, that is already one of the lowest pressure areas on the car, and air will flow out of there plenty if it has a way in. VW did a lot of drag work that they documented in SAE papers (that I used to have), and found that rounding the A pillars was a really big drag reducer, so you want a set of A pillars that look like the car in your pic. Spoiling the air at the A pillar would make the car look wider to the air, and it wouldn't reattach near the back, so you will get a lot of drag from a lip at the front edge of the window. Better to to put more curvature in the B pillar and reattach it, and then leave the smallest hole in the air at the back of the car to reduce drag.

Years ago cars had gutter lips that faced forward on the A pillar to prevent rain from coming around the A pillar and entering the back of the car, if you were crusing in light rain with the windows open. Mercedes found that they could round the A pillar and reduce drag, and made a catch step near the windshield to channel rain up over the top, and you see that feature in a lot of cars today.

Lots of air will flow out the front of the A pillar area, but it has to have a way to get into the car, and that is what you need to do if you have too much internal heat or fumes in the car, get some more air into the interior via cowl ducts or a window duct and you have the lower drag solution.