Are downpipes worth it if ...?

n54fanatic · 11-30-2010, 04:03 AM

i get that if you go with just catless downpipes on an otherwise stock exhaust its not gonna sound a lot louder just gain 20 rwhp. but will the catless downpipes make the car smell... i just bought a pair of ar design catless downpipes this post got me thinking if itll still smell like sulfur after the exhaust goes through the secondary cats?? anyone have any experiences running just a catless downpipes on an otherwise stock exhaust.

Black Sheep · 11-30-2010, 11:20 AM

I just ordered some AR pipes cant wait to get them in

ETS Michael · 11-30-2010, 12:11 PM

Anyone have a link with 2.5" downpipes vs 3.0" downpipes. I'm curious to see the difference between the two. It seems that 2.5" downpipes should be more then enough for the stock turbochargers.

I would be interested to see some dyno results.

Michael

OpenFlash · 11-30-2010, 12:14 PM

Quote:

Originally Posted by ETS Michael

Anyone have a link with 2.5" downpipes vs 3.0" downpipes. I'm curious to see the difference between the two. It seems that 2.5" downpipes should be more then enough for the stock turbochargers.

I would be interested to see some dyno results.

Michael

+1

BrianMN · 11-30-2010, 12:26 PM

Quote:

Originally Posted by ETS Michael

Anyone have a link with 2.5" downpipes vs 3.0" downpipes. I'm curious to see the difference between the two. It seems that 2.5" downpipes should be more then enough for the stock turbochargers.

I would be interested to see some dyno results.

Michael

http://www.e90post.com/forums/showthread.php?t=316974

It does seem the 2.5" downpipes would be adequate for 500+hp,but does that mean that larger won't yield more power?

I have a set of AR dps to replace my 2.5", and will have another dyno comparison.

momstmg78 · 11-30-2010, 01:18 PM

I just ordered ar catted dps. What kind of difference would be expected between catted and catless? Thx in advance. I've also ordered a hpf fmic also.no tune as of yet. Leaning towards procede.

ETS Michael · 11-30-2010, 06:21 PM

It seems funny to run 3.0" downpipes then reduce the pipe down to 2.5" at the flange for the 2.5" exhaust system. Removing the cats from the system should be the most bang for your buck mod on the exhaust system even with 3.0" piping I doubt you will see a huge if any differences since they reduce down to 2.5"

Michael

BrianMN · 11-30-2010, 07:10 PM

Quote:

Originally Posted by ETS Michael

It seems funny to run 3.0" downpipes then reduce the pipe down to 2.5" at the flange for the 2.5" exhaust system. Removing the cats from the system should be the most bang for your buck mod on the exhaust system even with 3.0" piping I doubt you will see a huge if any differences since they reduce down to 2.5"

Michael

Well you're still getting a bit more room for the ~16 inches after the turbos...which is an important area. But I agree the cat's are without a doubt the biggest impact.

ETS Michael · 11-30-2010, 07:37 PM

Dual 2.5 inch

Pi x 1.25 x 1.25 = 4.9 x (2) pipes = 9.8
equivalent flow to a single 3.5" inch exhaust

Shouldn't have any problem with back pressure

tibra1 · 12-09-2010, 02:08 PM

Quote:

Originally Posted by ETS Michael

It seems funny to run 3.0" downpipes then reduce the pipe down to 2.5" at the flange for the 2.5" exhaust system. Removing the cats from the system should be the most bang for your buck mod on the exhaust system even with 3.0" piping I doubt you will see a huge if any differences since they reduce down to 2.5"

Michael

I gotta think that having a 3 inch downpipe that tapers down to a 2.5 inch exhaust is better for exhaust gas velocity then a 2.5 dp to a 2.5 exhaust? Considering ur using catless dps ofcourse.

It seems like simple physics, but then again nothing is simple w exhaust science :/

Drakos · 12-09-2010, 02:16 PM

Here is a simple vid with just AR DP's and the golf tee mod. It def sounds better than stock. Will prob get an AE exhaust setup in the spring.

11-30-2010, 04:03 AM	#23
n54fanatic Captain 150 Rep 807 Posts Drives: M4 Join Date: Nov 2009 Location: SoCal iTrader: (2)	i get that if you go with just catless downpipes on an otherwise stock exhaust its not gonna sound a lot louder just gain 20 rwhp. but will the catless downpipes make the car smell... i just bought a pair of ar design catless downpipes this post got me thinking if itll still smell like sulfur after the exhaust goes through the secondary cats?? anyone have any experiences running just a catless downpipes on an otherwise stock exhaust.
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11-30-2010, 11:20 AM	#24
Black Sheep A Zip an a Double Cup 80 Rep 4,462 Posts Drives: 2009 BMW 135i Join Date: Feb 2010 Location: McHenry, IL iTrader: (5)	I just ordered some AR pipes cant wait to get them in __________________ PTF Tuned \| RB's \| AMS FMIC \| AR DP's \| HPF Exhaust \| CP-E DCI \| Apex Arc 8's \| 235/275 Star Specs \|
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11-30-2010, 12:11 PM	#25
ETS Michael Major 80 Rep 1,155 Posts Drives: 335i Join Date: May 2009 Location: Vancouver, WA iTrader: (4)	Anyone have a link with 2.5" downpipes vs 3.0" downpipes. I'm curious to see the difference between the two. It seems that 2.5" downpipes should be more then enough for the stock turbochargers. I would be interested to see some dyno results. Michael
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11-30-2010, 01:18 PM	#28
momstmg78 Banned 12 Rep 376 Posts Drives: 335i sedan Join Date: Oct 2010 Location: Turkish's house iTrader: (0)	I just ordered ar catted dps. What kind of difference would be expected between catted and catless? Thx in advance. I've also ordered a hpf fmic also.no tune as of yet. Leaning towards procede.
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11-30-2010, 06:21 PM	#29
ETS Michael Major 80 Rep 1,155 Posts Drives: 335i Join Date: May 2009 Location: Vancouver, WA iTrader: (4)	It seems funny to run 3.0" downpipes then reduce the pipe down to 2.5" at the flange for the 2.5" exhaust system. Removing the cats from the system should be the most bang for your buck mod on the exhaust system even with 3.0" piping I doubt you will see a huge if any differences since they reduce down to 2.5" Michael
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11-30-2010, 07:37 PM	#31
ETS Michael Major 80 Rep 1,155 Posts Drives: 335i Join Date: May 2009 Location: Vancouver, WA iTrader: (4)	Dual 2.5 inch Pi x 1.25 x 1.25 = 4.9 x (2) pipes = 9.8 equivalent flow to a single 3.5" inch exhaust Shouldn't have any problem with back pressure
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12-09-2010, 02:16 PM	#33
Drakos Lieutenant 68 Rep 534 Posts Drives: 2022 G42 M240i Join Date: May 2009 Location: Canada iTrader: (1)	Here is a simple vid with just AR DP's and the golf tee mod. It def sounds better than stock. Will prob get an AE exhaust setup in the spring.
	Appreciate 0 Quote