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iCarbon N55 Downpipe Review


11182010, 12:56 PM  #46  
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11182010, 01:05 PM  #47 
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Excellent Work. Real quality! It looks trick! Now if you would only fabricate some N54 Z4 downpipes... :P
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11182010, 08:13 PM  #48 
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i want a DP but not sure if i should wait or buy now ? dammmm
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USED TO HAVE A 385 whp 479 tq N55 335 2011 (AT) AND NOW A 135 M package 2010 (AT) 447whp/504tq

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11182010, 08:56 PM  #49 
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11182010, 09:10 PM  #50  
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Both downpipes delete the cat, so the source of the biggest restriction is gone in both DPs. Is there something that I'm missing? 

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11182010, 09:28 PM  #52  
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As for n54 (dual) downpipes, the notion that 3" pipes will outperform 2.5"pipes is funny considering each downpipe only needs to channel half the exhaust flow. But the idea of "bigger is always better" sells to those who don't know any better. Shiv 

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11182010, 09:32 PM  #53  
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11182010, 09:38 PM  #54 
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Dual catless 2.5" vs. dual 3.0" ID downpipes doesn't really matter to me. Both are adequately sized to easily support 250bhp (x2). Besides, the 3.0" downpipes taper back down to 2.5" where the meet up with the midpipes. Granted, the downpipes have a pretty sharp bend. Which makes 2.5" more appealing than the 2.25" that would usually be associated with that perbank power level.

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11182010, 09:43 PM  #55  
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11182010, 09:44 PM  #56 
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11182010, 09:52 PM  #57  
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Someone (sorry, don't remember whom) posted this link a couple of weeks ago and I found it extremely interesting. Here's a quote: Quote:
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If I recall correctly, someone on this Forum had custom 3" midpipes done that tapered down to 2.5" at the mufflers. I suppose such setup could have easily handled over 500whp given the reduced backpressure caused by moving the taper so far down the exhaust. Walter
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2013 E92 M3  6MT  AlpWhite  SilverNovillo  CarbonTrim  ZCP  PremiumPkg  Alarm
2009 E92 335i  6MT  AlpWhite  CoralRed  AlumTrim  MSport  Nav  Logic7  Alarm (sold to a friend  still in the family) 

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11182010, 09:58 PM  #58  
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11182010, 10:04 PM  #59  
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But it's true that you do want to push ID transitions as far downstream as possible since that is where the exhaust is coldest and has the least velocity. But in the case of the n54's dual exhaust system where each downpipe is only flowing half of the total exhaust flow, even 2.5" is sufficient. Running dual 3" exhausts (downpipe+midpipes) wont help or hurt you anymore than running dual 5" exhausts. It's all overkill above a certain point. I think the most important point that Jay made is that you want to make the transition between the turbine output and the downpipe inlet as smooth as possible and then gradually flare it out from there. This would suggest that the idea exhaust system would start off at ~2.25" coming off the turbo, flaring out to 2.5" (or 3") and staying that diameter all the way to the dual tips. Shiv 

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11182010, 10:06 PM  #60 
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Spot on
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11182010, 10:53 PM  #61  
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Based on the transition smoothness part, I imagine that in our case slight (perhaps irrelevant) turbulence might be created with DPs with collectors larger than ~2.25". Thanks for the follow up Shiv. Walter
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11182010, 10:58 PM  #62  
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11192010, 12:49 AM  #63 
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If any of you is counting your pounds, this DP will save you about 5 pounds off the front of your 135/335i

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11192010, 03:05 AM  #65  
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http://www.e90post.com/forums/showthread.php?t=455010 

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11192010, 03:19 AM  #66  
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And why did mr. 5 gain hp using 3" dps over 2.5s? I'm not trying to hijack anything, I deal with HP Autowerks all the time and Harold is one of the best people I've ever had the pleasure of talking to and doing business with. I can't knock the fitment of it or the gains of it (18hp is nice), the only thing I'm criticizing is the use of an oem size flange which from the factory is a bottleneck to begin with. And 360/370 hp is it? Are you so sure about that? 3 years ago you said you were uncertain if we could break 400hp in an N54, and look where we are at now. Last edited by itsbrokeagain; 11192010 at 03:49 AM. 

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