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      12-16-2008, 07:29 AM   #1
MrHarris
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Aftermarket exhaust aerodynamics

Is there any noticeable aerodynamic disadvantage with the way the aftermarket exhausts are designed compared to the stock exhaust?
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      12-16-2008, 10:36 AM   #2
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I doubt it makes much of a difference, but this is something I took into consideration when purchasing the Eisenmann muffler. it seems to be a lot closer to the stock design than the other systems out there with two seperate (dare I say generic) canister mufflers.
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      12-16-2008, 04:22 PM   #3
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This is a concern I raised very early.

The diffuser and meshed part of the rear bumper conver are designed to work in conjuntion with the under body panels of the car. This system, along with the shape of the OEM exhaust canister provide one or more of the following:
  • Exhaust cooling
  • Differential cooling
  • Reduced drag
  • Downforce (prob very minor)

Changing the geometry of this area the way many aftermarket exhausts do will certainly change some of the above effects. For the better or worse we won't know but it WILL be differnt than BMW designed and engineered it.
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      12-16-2008, 04:45 PM   #4
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This is a concern I raised very early.

The diffuser and meshed part of the rear bumper conver are designed to work in conjuntion with the under body panels of the car. This system, along with the shape of the OEM exhaust canister provide one or more of the following:
  • Exhaust cooling
  • Differential cooling
  • Reduced drag
  • Downforce (prob very minor)

Changing the geometry of this area the way many aftermarket exhausts do will certainly change some of the above effects. For the better or worse we won't know but it WILL be differnt than BMW designed and engineered it.
+1

Exactly! I'm not a physicist or aerodynamicist but based on the fact that I've stayed at many holiday inn express hotels, in the case of aftermarket exhausts with separate canisters and nothing in between, you are actually promoting more differential cooling at the expense of increased rear underbody turbulence from the differential to the valence which increases drag and lift. Very minimal to make a whole lot of difference on a 3700lb car in the course of a lap so I don't think it's anything to worry about.
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      12-16-2008, 04:48 PM   #5
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+1

Exactly! I'm not a physicist or aerodynamicist but based on the fact that I've stayed at many holiday inn express hotels, in the case of aftermarket exhausts with separate canisters and nothing in between, you are actually promoting more differential cooling at the expense of increased rear underbody turbulence from the differential to the valence which increases drag and lift. Very minimal to make a whole lot of difference on a 3700lb car in the course of a lap so I don't think it's anything to worry about.
???
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      12-16-2008, 07:05 PM   #6
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^ I was wondering what that meant too lol.
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      12-16-2008, 07:25 PM   #7
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^ I was wondering what that meant too lol.
humor.....haven't seen the commercials I'm guessing.
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      12-16-2008, 08:02 PM   #8
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^ I was wondering what that meant too lol.
It's from a Holiday Inn advertising campaign that jokingly implies that the mere fact of staying at a Holiday Inn will leave you so rested that you have more time and energy to excel at everything.
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      12-16-2008, 09:42 PM   #9
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LOL! Damn, I guess some of you don't watch any TV at all. Those Holiday Inn Express commercials are everywhere and have made its way well into pop culture and everyday conversational humor in the workplace, etc. Kinda like "I just saved a bunch of money on my car insurance" Geico commercials. Corny I know.
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      12-16-2008, 10:59 PM   #10
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LOL! Damn, I guess some of you don't watch any TV at all. Those Holiday Inn Express commercials are everywhere and have made its way well into pop culture and everyday conversational humor in the workplace, etc. Kinda like "I just saved a bunch of money on my car insurance" Geico commercials. Corny I know.
Haven't made it into my culture. Hey, but with free internet and a breakfast bar (per the website) you're good to go!
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      12-17-2008, 08:13 AM   #11
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The BMW release says that the factory rear muffler was designed to have the specific effects of rear diff cooling, lower underbody drag and a downforce effect. Read into that what you will
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