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Old 01-16-2011, 04:58 PM   #1
ScubaruImpreza05
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Question Exhaust wrapping... what do I need?

Possibly might need to wrap my 2.5i stock exhaust down to the catalytic converter. Have some questions since I did not see it addressed in the FAQ and couldn't find it in my searches.

1.) How much much wrap (assuming I am buying 2" wide stuff) would I want to get to wrap the headers from the block all the way to the catalytic converter? 50 feet? 100 feet? more?
2.) I have read people use metal ties or welding wire? What would I want to get?
3.) Do I need any sort of 'glue' or soak for the wrap when I apply it?
4.) Any other advice?

I may be doing this in conjunction with a catalytic converter gutting. I am hoping to fix an issue that leads to the conclusion that my cat is bad. I am getting about 15MPG right now after p0420 CEL, not cool.

PS - Anyone have a picture or link to a picture of the 2.5i exhaust to atleast the cat? I can't find any anyhere.
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Old 01-16-2011, 05:13 PM   #2
flightwatch
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Have you thought about getting it coated instead? I was originally going to wrap my header, but after hearing bad things about it (corrosion, flammability, etc) I got it coated.

Also, the stock exhaust manifold incorporates a cat into its design. I wouldn't suggest gutting that one as it will screw up your fuel trims...especially your LTFT which is derived from your rear o2 readings.

The second cat is further back in the mid-pipe, butI don't know what kind of gains (if any) you would see from gutting it.
Here is a pic of the stock '06 2.5i manifold:


And the stock mid-pipe:
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Old 01-16-2011, 05:34 PM   #3
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Hmmm, that sucks. I was thinking of gutting the midpipe cat. It doesn;t really look feasible to gut the front ones.

So, what if the front cats are the issue? Is that common or even heard of? I need to figure out why the heck my car threw the code and now is getting the MPG of an Expedition

Uncle Scotty suggested the code meant I had a partially blocked/bad cat. Is there a way to figure out which one it would be?

PS - thank you for the pics! They help out alot, I'm a visual kind of guy!
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Old 01-16-2011, 05:51 PM   #4
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So basically, I would want Borla headers or knock-offs, with the heat wrap then?

If the front o2 sensors would be screwed up by gutting the cats, wouldn't the Borla's produce the same results? Also, won't the UEL basically negate the performance gains over the EL stockers, or would eliminating those front cats make a big difference in conjunction with a gutted mid cat pipe?
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Old 01-16-2011, 06:27 PM   #5
flightwatch
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The front o2 isn't affected by the cats since it's in front of them. The borla reps or any other uel is meant for the sound. They will mess up your o2 readings since you have to move the sensors much further back in the exhaust than stock. (you will have to get tuned for the difference to negate the errors. I actually lost performance from the uel setup.
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Old 01-16-2011, 06:48 PM   #6
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So us 2.5i guys are screwed? Kind of blows. There is not point spending money to not gain anything and still screw up the reading. Just frustrating.

If I wrapped the stock setup and just reset the ECU, would it help anything? From what I have researched the p0420 deals directly with the rear sensor, so it isn't the front 2, or so I assume so.

PS - this thread I started yesterday has my o2 readouts through the OBD2 reader. maybe someone can figure out if it is a sensor or what. http://forums.nasioc.com/forums/show....php?t=2117694 (towards bottom is pics of my actron during live reading)

Last edited by ScubaruImpreza05; 01-16-2011 at 06:56 PM.
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Old 01-17-2011, 07:21 AM   #7
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As I understand it, the rear o2 sensor is just there to monitor cat efficiency. The front o2 is what determines the fuel trims and everything. A P0420 code is just the ECUs way of saying the rear signal doesn't match what it expects given what it's reading from the front sensor, which means it could be the rear sensor, the cat, or the front sensor.
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Old 01-17-2011, 08:48 AM   #8
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Yeah dude you can wrap your stocker but if you have the stock heat shield on it there is no point. All 2.5i Stock manifold are very well insulated against heat and noise. Under that 409 heat shielding is fiberglass packing, so it is a solid piece. You could gut the stock upstream cat as you have one more directly downstream of the Primary but you won't see many HP's as a result.

The rear O2 sensor is a check sensor nothing more you can tap behind the second cat and move the sensor there after gutting the primary, you can buy a new stock manifold $400, or you can go custom and move the cat to the mid-pipe.


A tip for wrapping: soak it in water (or even hi temp header paint) then wrap it and use the metal crimp clamps or screw clamps to secure it. The horror stories about it being flammable are from guys that allow oil leaks to persist and saturate the wrap then it ignites due to high temps. DO not base you choice off these accounts as they are clearly user stupidity A proper wrap job will last 2 years easily even through winter road treatments.
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Old 01-17-2011, 09:12 AM   #9
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Also if you have less than 80K you can get your cat replaced under emissions equipment warranty it will save you headache and there is nothing like a new cat for free
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Old 01-17-2011, 12:42 PM   #10
flightwatch
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In newer cars ('06+,) the rear o2 does more than check cat efficiency. It also helps calculate LTFT. Don't believe me?? Unplug your rear o2 for a tank of gas and watch those mpg's go South.
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Old 01-17-2011, 01:12 PM   #11
GEE-OTTO
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Actually you are right the rear downstream sensor is adversely affected when people go UEL and move that rear senor to a non OEM cat, it has to be corrected by tuning.

Curious if the sensor read below threshold and throws P0420 would it still exhibit the terrible MPG symptom?
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