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All You Need to Know About Downpipes

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All You Need to Know About Downpipes

Old 12-18-2009, 10:46 PM
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All You Need to Know About Downpipes

If a mod approves it and stickies it, this will hopefully be the Downpipe thread to end all other Downpipe threads.

What is a Downpipe?

The downpipe is the portion of the exhaust that connects the turbo to the rest of the exhaust system (cat-back exhaust). On our cars the dowpipe comes from the factory with two Catalytic Converters on it (more on Catalytic Converters http://en.wikipedia.org/wiki/Catalytic_converter) their main purpose is to help reduce the emissions coming out of the tail pipe, because of this they do restrict the flow of exhaust gases and because were all about making more power that's a bad thing. The stock/factory downpipe is the most restrictive component in our exhaust system. Replacing the downpipe with an aftermarket unit will greatly improve the flow of exhaust gasses out of the engine and in turn help us make more power anywhere from 10-15WHP and 10-15WTQ if tuned for the downpipe, on stock cars and cars with GMS1 or other canned tunes (Superchips, PPC, ZZP) the downpipe will most likely not add much power if any at all (read advantages/disadvantages section below). Below is a picture of a stock downpipe from a 2008-2010 Cobalt SS Turbo





If you plan on upgrading you basically have 2 main options here and they are as follows:

Catted Downpipe

An aftermarket catted downpipe may be purchased, these downpipes remove the (2) stock factory Catalytic Converters and replace them with one High Flowing unit, these downpipes also get rid of that little dimple you see by the O2 bung (which also reduces flow). If you have strict emissions laws in your state/province this is probably going to be your best bet as the high flowing catalytic converter helps you meet your emisions targets but flows significantly more than the stock cats do. These downpipes are louder and in my opinion better sounding than the factory exhaust and they do improve exhaust gas flow and in turn help us make more horsepower.

http://www.youtube.com/watch?v=YhtirXSzZCs (Cold start up)
(If anyone has a sound clip or video of a catted downpipe with a stock exhaust please let me know and I'll put it in)
Video


CIA Shown


Catless Downpipe (commonly called Off-Road)

An aftermarket catless downpipe may be purchased, these downpipes remove the (2) stock factory Catalytic Converters and replace them with a straight mandrel bent 3" pipe they also remove the dimple you see by the O2 bung. If you don't have strict emissions laws in your state/province or your just a rebel this downpipe may be your best bet. These downpipes are a little louder than the catted downpipe they provide more of a deeper gurgle type tone and yes they do improve exhaust gas flow and in turn help us make more horsepower, the catless downpipes can help us make an additional 1-3hp over an aftermarket catted downpipe (if tuned) because they have no cats at all.

http://www.youtube.com/watch?v=4Glk6jXowoA
http://www.youtube.com/watch?v=iw2ODRztqkg (Catless w/ Cutout Option)
http://www.youtube.com/watch?v=I2byHMos08A (Cold start up)
http://www.youtube.com/watch?v=jGfskjEeOLM
(If anyone has more sound clips or videos of a caless downpipe with a stock exhaust please let me know and I'll put it in)
Video


OTTP Shown

Advantages of an Aftermarket Downpipe (catted and catless)

- Improved exhaust gas flow = more power (again only if the DP is tuned for by Trifecta or HP Tuners)
- Stock cars or cars with canned tunes (GMS1, Superchips, PPC, ZZP) will see some power gains in the mid range but probably wont see any peak power gains
- Improved sound (Catless sounds great, Catted sounds great as-well but slightly muffled)
- Faster turbo spool up (slightly)
- Weight savings over stock downpipe

Disadvantages of an Aftermarket Downpipe (catted and catless)

- Potential of throwing a Check Engine Light (if catless) I'll talk more about this later
- Increased emissions (if catless)
- Possible odurs from exhaust (if catless)
- Cost
- Louder than stock
- Possible warranty issues

O2 Bung/Chamber

The O2 Bung/Chamber is the threaded hole where the Oxygen Sensor (O2 for short) sits. The design of it is important especially on a catless downpipe if the O2 sensor does not like what it's reading like when there is no Catalytic Converter infront of it it may trigger a Check Engine Light (CEL for short), which can be cleared via a code reader/clearer (can be picked up for relatively cheap) or completely disabled via HP Tuners [if anyone has the link to the thread talking about CEL's for this please let me know]. If the thought of having to go get your CEL cleared or disabled scares you, you should probably just go the safe route and get a catted downpipe. Some vendors offer an angled O2 Bung/Chamber (usually for an extra cost $20-50) which limits the amount of exhaust gasses the O2 sensor sees this helps reduce the chances of getting a CEL especially with a catless downpipe I highly recommend getting the angled O2 chamber if getting a catless downpipe shown below:


OTTP Shown

Other things you should know about

Electric Cut-Out
Some vendors offer an option for an electric cut-out which is welded into the downpipe, what this does is let you via a switch mounted in the cabin by-pass the whole cat-back exhaust and vent your exhaust gasses right at the downpipe this improves exhaust flow however it makes the exhaust very loud and should probably only be used at the track unless you want a nasty ticket.

Second O2 Bung
If you have a wideband that you want to use some vendors offer the option to weld in a second O2 bung into which the wideband can be plugged in. This second O2 Bung is welded in before the Catalytic Converter.

Aluminized or Stainless Steel
If your on a budget or you don't plan on keeping the car for very, very long you can go ahead and get an aluminized downpipe as it is cheaper because it is more prone to rust. However if you never want your downpipe to rust or stop looking pretty get stainless steel.

Spun Metal Cat
Smaller higher quality Catalytic Converter offered by some vendors.

Where can I buy an aftermarket downpipe?

There are many vendors that sell downpipes as far as I can tell there isn't a big difference in between them all the main one being catted or catless and O2 Bung/Chamber design options. Here is a list of the ones I have heard of (in alphabetical order to prove that I am not favoring a particular brand):

CIA (Clear Image Automotive)
http://www.clearimageautomotive.com/...%20SS%20TC.htm
Catted, Catless, Electric Cut-Out, Aluminized or Steel Options

Dejon
http://cobalt.dejonpowerhouse.com/
Only Catless

Exhaust Depot
http://www.exhaustdepot.net/cosstudo.html
Catted or Catles Options

Hahn Racecraft
http://www.turbosystem.com/ProjectVe...TCdownpipe.htm
Lots of options

Modern Performance
http://www.modernperformance.com/081...c-473_599.html
Catted or Catles Options

OTTP
http://www.ottperformance.com/store/...ipe-27p908.htm
Catless, O2 Chamber Design, Wideband O2 Bung Options
*Myself and other members on this forum have had fitment issues with the OTTP Catless DP which OTTP has been less than eager to resolve properly* (Just a heads up)

Synapse Turbo
http://www.synapseturbo.com/mm5/merc...ode=downpipegm
Only Catless

ZZP
http://www.zzperformance.com/cobalt_...1016&catid=155
Catted, Catles, Spun Metal Cat, O2 Chamber Design, Wideband O2 Bung Options

(If I didn't list all of the vendors or some should be taken down please let me know, also if there is any information that is missing and or wrong please let me know and I will fix it)


How do I install a downpipe?

You can either do it yourself if you have some mechanical abilities and some basic tools (Here is a link to a very good how to https://www.cobaltss.net/forums/how-guide-43/how-cia-down-pipe-warning-big-pics-160726/) or take it to your local exhaust shop.

Last edited by tom.g; 08-08-2010 at 02:50 PM. Reason: New Info
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Old 12-18-2009, 10:51 PM
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well written..Sticky definatley! please!
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Old 12-19-2009, 02:47 AM
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Originally Posted by TCguy View Post
well written..Sticky definatley! please!
I agree. Excellent info!
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Old 12-19-2009, 10:05 AM
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Please someone sticky this^^^
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Old 12-19-2009, 10:16 AM
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Bout time someone did this to avoid constant new posts..

I think you should add "Possible foul odors" to the disadvantages of catless. Although these don't seem to smell as bad as other cars I've been around, catless cars often produce strong and overwhelming odors some people might not like.
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Old 12-19-2009, 11:26 AM
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omg thank you so much. Someone sticky those so ******* newbies stop asking the same questions
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Old 12-19-2009, 12:08 PM
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Sticky, nice write up.
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Old 12-19-2009, 12:14 PM
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My god this needs to be stickied ASAP!...I would probably suggest plopping it in the LNF section instead but either way works...this may be the solution to all the n00bs not using the search button! Very nice write-up. This restores a little faith in the intelligence level on this site!
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Old 12-19-2009, 12:19 PM
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now all we need is a thread like this but on tuning and one on intakes and we will be set
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Old 12-19-2009, 12:23 PM
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amen! haha
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Old 12-19-2009, 12:46 PM
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sticky sticky sticky
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Old 12-19-2009, 04:01 PM
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Definitely a great write up! Thanks!
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Old 12-19-2009, 07:21 PM
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Originally Posted by ssilver View Post
Bout time someone did this to avoid constant new posts..

I think you should add "Possible foul odors" to the disadvantages of catless. Although these don't seem to smell as bad as other cars I've been around, catless cars often produce strong and overwhelming odors some people might not like.
Thanks, info has been added
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Old 12-21-2009, 12:46 PM
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Bump and vote for sticky
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Old 12-22-2009, 12:22 PM
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Bump.. STICKY PLEASE !!!!
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Old 12-22-2009, 03:12 PM
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Great Job! STICKY!!!
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Old 12-24-2009, 10:30 PM
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Originally Posted by slowbalt84 View Post
now all we need is a thread like this but on tuning and one on intakes and we will be set
agreed.
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Old 12-25-2009, 01:22 AM
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Great Thread!
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Old 12-25-2009, 01:31 AM
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Agreed on Sticky
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Old 12-25-2009, 08:35 PM
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Sticky bump
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Old 12-26-2009, 04:09 PM
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Thanks to IsItFast? for a new video of a Catless DP with a cutout option!
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Old 12-27-2009, 01:04 PM
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Were on the downpipe should the wideband O2 Bung get welded. Before or after the CAT?
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Old 12-27-2009, 07:39 PM
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Originally Posted by Vee's SS View Post
Were on the downpipe should the wideband O2 Bung get welded. Before or after the CAT?
After the cat.

Last edited by tom.g; 12-27-2009 at 09:38 PM. Reason: As per Terminator2
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Old 12-27-2009, 08:11 PM
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Originally Posted by Vee's SS View Post
Were on the downpipe should the wideband O2 Bung get welded. Before or after the CAT?
Before the cat. If it is installed after the cat it will show leaner than actual A/F.
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Old 12-27-2009, 09:36 PM
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I need to get a video up soon of my Dejon 3" Catless Downpipe with a cutout....
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