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More DX / EX exhaust fun

  #1  
Old 05-14-2011, 05:59 AM
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Default More DX / EX exhaust fun

Perhaps my search skills suck, but I haven't been able to find anything on this...

Is there some reason why a DX owner can't us an EX cat-back exhaust by shortening the down tube (the one with the bend in it, after the DX's stock cat) and adding a cat flange at the distance where the EX cat would have been? Seems like it would save you a whole lot of heartache of exhaust manifold swaps and messing with the O2 sensors...

FYI: Don't care about [beyond stock] performance, just that the aftermarket catback exhaust are cheaper than the honda pipes when the center of your exhaust rusts out!

x

[00 civic dx, MT]
 
  #2  
Old 05-14-2011, 07:29 AM
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  #3  
Old 05-14-2011, 08:23 AM
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Yes. I'm trying to avoid the pain of everything described in there. O2 sensors are expensive, as are manifolds and catalytic converters.

If you look at the first diagram... the item labeled "downpipe". Why can't you shorten it and add a 3 bolt flange like the cat has with a welder? Am I missing something? If the resonator in the way?

The "detailed thread" link in the article you referenced has the guy adding a flange to use the DX downstream exhaust with the EX manifold / cat. I want to do the opposite, but am unsure if there is a gotcha. I would like to know before I cut the down tube.
 
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Old 05-16-2011, 04:48 PM
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No responses. I find it nearly comical that no one has attempted this, vs. purchasing an ungodly number of parts.

1) The easy part. Remove your old exhaust system you will want to leave the "down tube" in place. Keep the long strait section of pipe after the down tube close by, we're going to need to measure it for a cut. From hear on out I'm going to call it "st-res" for straight resonator [pipe].

Notice the first problem: the catalytic converter end ['cat'] has a 3 bolt flanges and everything else has a 2 bolt flange.


2) We're going to need a new 3 bolt flange to mesh everything up. The cat flange gasket makes a nice item to trace into 1/4" plate for the flat flange (my catback system didn't use the donut flanges):


The plate came from Lowe's. We'll get back to that in a second

3) Test fit the new system. I used zip ties in place of the rubber mounts for the fitting:


I also finger tightened all the flanges without using the gasket. It's important to note that finger tight doesn't mean let it slop. Slop will throw off the measurements in the next step, as will to much hang in the ties. Tighten up the ties after everything is hanging to get the exhaust hanging close to where the stock pipes were.

4) Compare where the end of the EX system is with the st-res pipe and mark it. This is where the st-res pipe needs to be cut. It should be before the heat shield, so don't worry about removing the shield:


Tomorrow I'll hopefully be able to cut the st-res pipe and finish fabricating the flange.
 

Last edited by xuare; 05-16-2011 at 04:54 PM. Reason: Mistake. the downpipe was used in place of the first long section of pipe after the "down tube"--correcting
  #5  
Old 05-16-2011, 04:58 PM
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One other side note: my st-res pipe rusted through just before the resonator. This will make my section of that pipe _much_ shorter than a stock one. Also the rest of my st-res pipe is rusty on the bottom. I am going to invert my section of pipe of the condensed water is in contact with a different part of the piping. This is do-able because the st-res pipe connects to the down tube with a 2 bolt flange (invertible) and the section of pipe I am going to be reusing is straight.
 

Last edited by xuare; 05-16-2011 at 04:59 PM. Reason: typo
  #6  
Old 05-18-2011, 12:40 PM
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good luck! keep us posted on how it turns out.
 
  #7  
Old 05-18-2011, 02:35 PM
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If I recall right, the DX downpipe is already shorter than the EX downpipe. So you would actually have to lengthen the downpipe or fabricate a separate piece for it to reach the point where it would bolt up to the rest of the resonator/pipe/etc. However, if you wanted to fabricate something to work that way instead of using a bolt-on solution, that's your prerogative. Most people like the easy, bolt-on route. I'm more of a DIY guy, myself, though.

The easiest way is to get a salvage EX header and catalytic converter and bolt that onto the catback system. You would reuse your O2 sensors and just get an extension harness for the one that's furthest from the harness. That gives the full benefit of a slightly larger, better flowing exhaust system. The DX header/cat combo will still be a bit restrictive in the setup you are suggesting.
 
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Old 05-18-2011, 06:19 PM
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Originally Posted by WellFedHobo View Post
If I recall right, the DX downpipe is already shorter than the EX downpipe. So you would actually have to lengthen the downpipe or fabricate a separate piece for it to reach the point where it would bolt up to the rest of the resonator/pipe/etc. However, if you wanted to fabricate something to work that way instead of using a bolt-on solution, that's your prerogative. Most people like the easy, bolt-on route. I'm more of a DIY guy, myself, though.

The easiest way is to get a salvage EX header and catalytic converter and bolt that onto the catback system. You would reuse your O2 sensors and just get an extension harness for the one that's furthest from the harness. That gives the full benefit of a slightly larger, better flowing exhaust system. The DX header/cat combo will still be a bit restrictive in the setup you are suggesting.
Yes, the downpipe itself is not long enough. The pipe after it, which is mostly straight and has the resonator needs to be sacrificed. I'm calling this pipe the "st-res" pipe for straight resonator pipe. It's the one I'm "shortening" and adding the flange to. In my case it already rusted through so it has no worth to me anyway. I'm also not wanting to make my car a performance car. I personally would not pick a civic for sporting purposes (I'm omitting details to avoid a flame war)

It been raining so I have made little progress. The biggest downer was my drill press vice wasn't big enough to hold the plate steel flange, so I'll have to try a workaround so I can cut out the ID.
 
  #9  
Old 05-26-2011, 04:30 PM
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On vacation, hope to show more when I get back.

Some notes: The exhaust was actually 1 7/8" on my DX so I needed as expansion adapter to get to 2 1/4", procured at Advance Auto Parts. I welded it in place. I also tac welded the flange I made to the vice for drill pressing, which worked well (again 2 1/4" hole saw bit).
 
  #10  
Old 05-26-2011, 04:39 PM
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Nice! Yeah, I used the write-up listed above because I don't have the skills or the tools to do what you did. I look forward to seeing the finished results. I hope you have a great vacation!
 

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