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      11-22-2010, 03:29 AM   #1
erics02wrx
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Drives: E90 M3
Join Date: Aug 2010
Location: Snohomish WA

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Arrow DIY: OEM x-pipe secondary cat removal/gut

Looking for an after market x-pipe with secondary cat delete and resonators for your car? How about modding your OEM exhaust! There is VERY LITTLE difference between the aftermarket x-pipes and the stock one! BMW has built a very good quality exhaust system from the factory and it needs only a few minor tweaks to squeeze out the extra hp. I was looking for a x-pipe with 2nd cat delete with resonators but could not understand how the manufactures could justify there pricing, they must think we have $ to burn or that most M3 owners just believe the hype and buy

The secondary cat delete (Gut the factory cats) is very easy and only took me about 3 hours total including removal, modifying and reinstall. This is one of the best improvements i have done to the car. It will make the engine more responsive and should add around 8-15hp for $0.00 and a little bit of your time. If you are not the DIY type then an exhaust shop should be able to do this for less than $150-200.

+ The best part is the dealer will have no clue it is modded, it looks stock


So here is the process of doing a secondary cat gut / delete:

1. remove the x-pipe portion of the exhaust from car, you can leave the rear sip-on exhaust on the car
2. you will need to mark the exhaust pipe with 2 or 3 parallel lines on each pipe because you will use these later when you are realigning the exhaust tubing for welding. Now using a cut off wheel, cut the slip joint right behind the weld at the front of secondary cats. Be careful and only cut through the outer pipe wall, not all the way through


3. now this is what the 200cell secondary cats look like


4. just for reference, these are the tools that i used

5. (PUT ON DUST MASK) take your 1/2 HD drill and use a 3/4" +/- self feed spiral drill bit to remove the majority of the catalyst. If you try to just pound it out it will compress into a hard metal mass that will lodge itself inside the exhaust tubing(trust me) Remove most of the catalyst material and then use the pipe to scrape and push out the left over material. You should have a pile of catalyst like this from the first cat

and this is what it should look like with the first cat removed/gutted

6. now do the same for the next one and your pile of catalyst on the floor should look like this

7. you will need to rig up a wire brush on a piece of pipe and clean-up the inside of the exhaust pipe, it doesn't need to be perfectly clean just get most of the catalyst out


8. now that you have the gut complete you are ready to reassemble

9. you should now be able to realign the exhaust using the alignment marks you made at the beginning. I used a small MIG welder to weld the exhaust tubing back together. You will need to do a series of tack welds around the exhaust tubing as to not burn through, or set your welder to the lowest setting, this is very common for exhaust tubing.



10. if you are trying to be stealth then nows the time to clean up the welds

and this is what it should look like, once it gets a Little heat coloring on it the dealer will have no clue that it is modded!


In addition to what I wrote at the beginning, I did this mod so that I would not have to deal with a CEL and then a tune, and the inevitable chance that the dealer will reflash the car while in for service. I would then lose my tune and have to pay for it to be reflashed to the ECU, its just not worth it to me for an extra 10-15 whp that a tune gives you. I will probably in time gut the main OEM cats also, I just need to find a good CEL fix that the dealer won't find. Most of the hp people are getting out of our cars are from the removal of the cats (20-30 whp) NOT THE TUNE! (10-15 whp). I drive my car hard at the track and I want to know that if something goes wrong with the car, the dealer will have less to complain about and no reason to say I voided my warranty.

Hope this helps some of you that are thinking of doing this mod.......
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Last edited by erics02wrx; 11-22-2010 at 11:52 PM.
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