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I know almost nothing about cars so sorry if this is a really stupid question, but I have NPP on a non-Z51 and always drive it in 'loud' mode. Just hit 500 miles and the 1st and 4th tail pipes are pretty dirty but the 2rd & 3rd are as shiny and clean. Curious why that is.

BTW what product do you guys use to clean them?
 

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I have NPP on a non-Z51 and always drive it in 'loud' mode. Just hit 500 miles and the 1st and 4th tail pipes are pretty dirty but the 2rd & 3rd are as shiny and clean. Curious why that is.
The majority of crud on #1 and #4 appears to be carbon mixed with water, which evaporates into a black stain as the engine/exhaust warm. I think this is prevalent on #1 and #4 because they are welded at a lower position on the muffler than #2 and #3, which makes #1 and #4 the preferred path for water exit.

BTW what product do you guys use to clean them?
I use Glen's procedure (Glen's exhaust tip procedure) with the buffing cone, but with Meguiar's "All Metal Polish". I use CQUK and Reload on the exhaust tips (I also use this product on my wheels) - they wipe clean, and I hit them with a reload application once a month.
 

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That actually makes sense Mobius...I alwasy thought it was becasuse of the NPP shutting the valves on the 2 muffled pipe tips on the interior and opening the 2 outer, louder pipes.
 

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That actually makes sense Mobius...I alwasy thought it was becasuse of the NPP shutting the valves on the 2 muffled pipe tips on the interior and opening the 2 outer, louder pipes.
Pretty much. Outer pipes open result in a pretty straight shot out of the muffler. When closed, all that junk gets dissipated Inside the muffler on it's way to the inner pipe outlets and consequently not so noticeable externally.

Theta pic:
npp-vi.jpg
 
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Pretty much. Outer pipes open result in a pretty straight shot out of the muffler. When closed, all that junk gets dissipated Inside the muffler on it's way to the inner pipe outlets and consequently not so noticeable externally.

Theta pic:
View attachment 10194
There is one other thing at play which keeps the inner two pipes cleaner on NPP systems, if the outer NPP valves are open.

It turns out that Bernoulli's principle manifests itself, and, get this, the airflows on the center two pipes are INTO the mufflers instead of out of the mufflers.

I just saw a YouTube video of this tonight. The guy and his girlfriend kept trying to blow up a - er... membrane... yeah, let's call it that - placed over exhaust tip number 2. However, each time he started the car and/or drastically increased the RPMs, the, er, "cylindrical protrusion of the membrane" would keep getting sucked back into the muffler instead of blowing out like a balloon like they desired. They could not figure out why.

Yelp, it's the same thing at work there that causes an airplane wing to develop lift and fly.

How cool is that?

-Rodney a.k.a "Dr. Nerd" over and out
 

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Makes sense, and it's difficult to argue with the experimental evidence.
 
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CEPupper, it's annoying and unsightly but it only takes me less than 30 seconds to quickly wipe off the residue before wheeling away.

SF
Rick
 

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I have Bullets, which delete the NPP, and my tips are equal opportunity carbon build-up points.
 
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