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A4/S4/RS4 B7 2005-2008

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  #21  
Old 18th July 2011, 07:47 PM
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Agree with most of that Doc, although I'm led to believe that the turboed cars benefit more from a full decat as the NA engines seem to need to bit of back pressure to operate at peak performance, hence why I went with 100 cell Milltek downpipes on the B6 S4.

I could of course be talking completely out of my bottom...
I think Doug from MRC recommended to RanjA8 to de cat his B6 S4 when he took it down, not 100% though.
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  #22  
Old 18th July 2011, 09:47 PM
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Has he supercharged it?
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  #23  
Old 19th July 2011, 08:20 AM
ainarssems ainarssems is offline
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I am no engineer but I do not see how back pressure can be better. Less pressure= more exhaust gasses can get out faster=emptier cylinder=more space for fresh air+fuel= more power. Correctly designed exhaust manifolds can even make negative pressure and suck exhaust gasses out. I can see how bigger pipe or removing cat can slow down gasses because of greater cross-section area reducing the suction effect and there-for evacuation of exhaust gasses.

Now 2 stroke engines are completely different case but that's another story.
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  #24  
Old 19th July 2011, 11:00 AM
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Has he supercharged it?
Nope, tried convincing him to either charge it or buy a B5 RS 4. But he didn't buy the 'RS' with fear of it getting nicked.
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  #25  
Old 19th July 2011, 01:41 PM
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Originally Posted by CliveH View Post
Agree with most of that Doc, although I'm led to believe that the turboed cars benefit more from a full decat as the NA engines seem to need to bit of back pressure to operate at peak performance, hence why I went with 100 cell Milltek downpipes on the B6 S4.

I could of course be talking completely out of my bottom...
If you go too large on the exhaust diameter you can have negative effects, but freeing up that lovely V8 and the noise..... oh the noise........

100 cell Millteks are a touch more legal tho!
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