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Don 944 LA's Avatar
 
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?? about aerodynamics and the crap on the back ???

Basically all you people " In the Know ", help me out with a dilema..

I constantly get debris all over the back of the 944.
I can clean it off daily, and its back tomorrow. Could it be stuff from the road being sucked up from under ???

Mind You, I'm not a " speed limit " driver. I also drive 300 miles a day, some of it wide open 100-110 MPH... can the aerodynamics of the car be doing that and if so, is some sort of add on panel that will remedy it ???

Thanks for all the help

Don

BTW, glad it's not a smog question ???
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Old 06-16-2004, 10:18 PM
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you mean your rear spoiler attracts dust and dirt?

must be the static electricity of air passing over the polyurethane rubber of the spoiler.
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Old 06-16-2004, 10:26 PM
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Nothing will remedy that. The rear of the car is a low pressure area so all of the dust that would normally pass over the car gets sucked in to the swirling air just under the spoiler.
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Old 06-16-2004, 11:32 PM
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Of course if you can get it supersonic, the shock wave will take care of it. . .
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Old 06-17-2004, 06:11 AM
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Something has to be coating the back for the dust to stick too. What oil leaks do you have?
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Old 06-17-2004, 07:15 AM
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(only need to do speed limit to conduct this test)

let your friend dirve your car in the rain, while you drive his car and follow off to the side and a little behind of your car. look at the rear to note that the rain will flow off the rear and float about 3-4 feet before it falls back down also there is some water that flows up from the tire and when it gets to the Low pressure zone it will hang and or swirl behind the car. i believe this is what happens when it is also dry out and dirt/oil/ whatever else is on the road gets cought in the Low pressure zone. thus making the rear end dirty and dirt sticks to everything(dirt roads make the rear of these cars look worse).

i did this test and thats what i noticed (but my friend and i dont use speed limits so it was tested at about 100+MPH). only cure i found for it was washing daily.
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Old 06-17-2004, 07:44 AM
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You could install a spoiler like old station wagons had that directs air down through the low pressure area . They did it on wagons to prvent all that crap from sticking to the back window.
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Old 06-17-2004, 08:54 AM
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Quote:
Originally posted by SoCal Driver
Something has to be coating the back for the dust to stick too. What oil leaks do you have?
Uh, let me put it this way, 1 qt Mobile 1 15W-50 every other day..

Thats about every 600 miles.

I actually pulled into a Mobile station at Camp Pendleton and they said " Check your oil ? " I haven't heard that in a long time, so the guy put in a qt for me.

so, the air rushing under picking up slight oil dropplets and then sticking to the back ???

BTW, its all over where the " 944 " is and all the way down to the bumper.

It comes off with one of those " California dusters "
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Old 06-17-2004, 06:41 PM
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Quote:
Originally posted by kdfoust
One thing that is cool about the aerodynamics of the car is that I've noticed at between 80-90 the rear window will clear of dew in seconds...
I'm one for pushing 120 in the 944, but I don't think I would hit 90 when I couldn't see out the back. Thats what the defrost is for. Although I would like to remove the defrost on the rear so that I could see better out of the window.
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944 85.0 Kalahari Beige -- Dead/Gone/NotForgotten (Ran Like a Raped Banshee) 944 85.5 Guards Red
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Old 06-17-2004, 06:44 PM
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When the diff seals went out on my first tranny, the same thing happened. I was putting 1/2 quart of tranny fluid in every other day.
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Old 06-18-2004, 02:12 AM
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My transaxle had a leak , same thing, had oil all over the rear of the car. once I changed the seals it was fine.
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Old 06-18-2004, 03:25 AM
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I was also dumbfounded why the rear of my car kept getting sooo damn dirty, thinking it was crap coming out of my exhaust. I asked my mechanic who explained to me that when the air travelling over the car gets to the rear spoiler it gets kicked 'upwards' (not exactly directly upwards but more at a 35degree angle). As a result of this the air has a higher pressure with the air below this, directly behind the rear of your car, having a lower pressure. Due to this the air at the rear of your car basically acts like a vacuum cleaner sucking up all the crap off of the road and 'sticking' it to the back of your car.

So really there isn't any way of keeping it off aside from driving slower :P buuuuuut i cant see many of us doing that so it looks like we'll just have to keep washing 'em.
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Old 06-19-2004, 02:05 AM
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You could always remove the spoiler like on the 924!
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Old 06-19-2004, 08:00 AM
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Installing a 944 rear valance (Euro) helps keep it clean and cleans up the rear view IMOP
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Old 06-19-2004, 11:27 AM
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Hey don, if you want to ditch the spoiler i got an old 924 glass hatch sitting around
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Old 06-19-2004, 05:38 PM
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Quote:
Originally posted by Brando
Hey don, if you want to ditch the spoiler i got an old 924 glass hatch sitting around
That may be an idea....

What would be the drawbacks of not having a spoiler on the hatch ???
I'm sure it serves some function.. Like keeping the rear end on the ground ??

Is there the same effect with a 968 rear spoiler ???
I've always liked the look of the 968 one.
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Current Stable 944 83 Kalahari Beige manual rack, short 5th gear951 86 Guards Red, pristine TurboYou must not anger the Porsche Gods - you MUST leave one small item unrepaired, lest the Stuttgartians smite thine car with bad Ju-Ju-AF Juvat
Old 06-19-2004, 06:16 PM
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Wow - you openly admitted you drive your Porsche at high speeds, and no one chewed your ass (yet) for doing so! There may be hope after all.....Yes, I am being a smartass and wholly endorse driving these cars in the manner for which they were designed...

Anyhoo...have you considered putting a 951 or Euro type lower valance on the car? It may alter the rear aero characteristics enough to reduce the problem. I have an S2 and have mainly owned 951s, and haven't noticed the problem.
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Old 06-19-2004, 09:43 PM
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Quote:
Originally posted by 72widebody
Wow - you openly admitted you drive your Porsche at high speeds, and no one chewed your ass (yet) for doing so! There may be hope after all.....Yes, I am being a smartass and wholly endorse driving these cars in the manner for which they were designed...

Anyhoo...have you considered putting a 951 or Euro type lower valance on the car? It may alter the rear aero characteristics enough to reduce the problem. I have an S2 and have mainly owned 951s, and haven't noticed the problem.
I was thinking along those lines..
does everyone think that would help ??

It's just a pain to clean the junk off everyday. Its only because I drive so many miles that it accumulates fast. I do use the duster, and it only takes a couple minutes.

Oh, I forgot, now that the sunroof isn't a freeway frisbee, I can run it through a carwash ( small leak- hold towel up by rear sunroof seal )..
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Current Stable 944 83 Kalahari Beige manual rack, short 5th gear951 86 Guards Red, pristine TurboYou must not anger the Porsche Gods - you MUST leave one small item unrepaired, lest the Stuttgartians smite thine car with bad Ju-Ju-AF Juvat
Old 06-20-2004, 09:43 PM
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A 968 spoiler wold also help because it lets air pass under but it still creates downforce. A 968 turbo one would be even better.
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Old 06-20-2004, 10:51 PM
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Yeah, looks like thats the best option...

do I have to change ALL the things around the rear glass ??
Or , just the spoiler/wing

hey, how bout I put a big ol' 4 foot whale tail !!!!.. yeah, thats the ticket...

-- too much vino

I could also add the headlight washing system and just re-route to the back. Hell, I can't even get my front washers working.
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944 85.0 Kalahari Beige -- Dead/Gone/NotForgotten (Ran Like a Raped Banshee) 944 85.5 Guards Red
Current Stable 944 83 Kalahari Beige manual rack, short 5th gear951 86 Guards Red, pristine TurboYou must not anger the Porsche Gods - you MUST leave one small item unrepaired, lest the Stuttgartians smite thine car with bad Ju-Ju-AF Juvat
Old 06-21-2004, 11:35 PM
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