Opened or closed rear windows when racing SWB car

[1QuickS]

Yes, dash vent open and door vents open as well. I find it hard to believe about the exhaust entering the car when at speed and windows open but this is my deduction.

Upon reflection, it might be my imagination and lack of earplugs...

[TheTorch]

I have experimented with all the permutations I can think of and I believe it to be exhaust wash coming in the drivers window, and noticeably worse with the rear vent window open. I have rebuilt the whole fresh air assembly, and the only time I don't get wash is with all the windows closed, or with the blower motor on 2-3 (which makes it's own annoying noise). If I have the fresh air vent open but no blower running -- exhaust almost regardless of speed. I have the stock single driver's side exhaust outlet.

Like Paul I keep wondering how the backwash makes its way forward at all speeds, but I swear it does. And I like most prefer to drive with my windows open.

I would love to be wrong here, so please fire away.

[1QuickS]

I was wondering when rear pop-out windows became fixed. The front quarter windows disappeared in 1969. Were rear pop-out windows un-cool, too expensive, facilitators of thievery, or possibly due to exhaust back-wash issues?

[edmayo]

Most sources say to save money.

[sithot]

I have experimented with all the permutations I can think of and I believe it to be exhaust wash coming in the drivers window, and noticeably worse with the rear vent window open. I have rebuilt the whole fresh air assembly, and the only time I don't get wash is with all the windows closed, or with the blower motor on 2-3 (which makes it's own annoying noise). If I have the fresh air vent open but no blower running -- exhaust almost regardless of speed. I have the stock single driver's side exhaust outlet.

Like Paul I keep wondering how the backwash makes its way forward at all speeds, but I swear it does. And I like most prefer to drive with my windows open.

I would love to be wrong here, so please fire away.

"Aerodynamic" thread on Pelican:

http://forums.pelicanparts.com/porsc...ml#post7477047

[1QuickS]

The image of the original 901 prototype with yarn flowing has rear pop-outs closed. When open they will create a pressure drop within the window opening due to the accelerated air across the open window, much like the pressure differential on an airplane wing. Also note the yarn strips become turbulent below the rear bumper which also points out the body itself is like a wing, accelerated air flows over the top of the body creating lift and air below the body is at a higher pressure. Potentially the low pressure of the open pop-out will draw air from below the rear bumper. The high pressure may direct air under the car which could carry exhaust fumes with it.

Another comment: One of my absolutely favorite features of the 911 is there is no buffeting of my ear when driving with the window down. I have owned Beetles, BMW 2002s, and four door sedans of German, Japanese and American origin and all will buffet my ear. My conclusion is air flows out of the driver's window or at least inrushing air enters behind my head. If the air flow is neutral or if it flows out the window then this would imply a negative cabin pressure which would also help suck exhaust into the cabin.

The duck tail and other aero improvements change the air flow characteristics but on the original chassis I think it is technically plausible to suck in exhaust through open pop-outs.

[John Straub]

I always keep the rears open. I don't know if it helps anything. I just think it looks cool! LOL!

John

[ejboyd5]

See a somewhat companion discussion: https://www.912bbs.org/forum/threads...he-roof.60754/

[Jay Laifman]

I might add that on my 912, I was so fond of those original orange foam tubes for the heater in the back of the engine compartment. And I felt comfortable that the full system was in great shape and adjusted well. But, at some point, I removed those tubes and the smell in my car changed dramatically for the better. I hadn't even really noticed it being bad. But the second I made the change, I noticed the improvement. I don't think that matters if the windows are open or not. But might we worth checking out too.

Since I don't really use the heater, I have the foam tubes back in, but the air is capped at the bottom. So nothing flows up into the passenger compartment.

[sanders]

911R quarter windows were vented.