eliminating main cats and resonators - do I need to code out G130/G131?

[kismetcapitan]

right, so I'm going to get the main cats chopped out and straight pipes welded in. I'm looking at the exhaust system diagram however, and the O2 sensors are *before* the cats...do I need to get these coded out? Or leave them and have them installed into the straight pipes?

And any thoughts about chopping out the resonators? My understanding has usually been that the resonators got rid of drone, and the end mufflers took care of silencing. Loudness is good, but droning exhausts on the highway gets pretty annoying.

Anyone with non-res exhausts, comments on the exhaust volume when cruising at 80mph for long periods of time? Is it still pretty quiet? (stock, it's dead silent, I can't even hear wind buffeting, just tire noise really).

What is going to be most cost-effective for me at this point to reduce backpressure and open up the exhaust note is to "cut and paste" - cut out the resonators and underbody cats, and weld in straight pipes. The SE muffler section will remain unmolested, and I'll eventually get around to getting rid of the precats and maybe even fab up a straight pipe final section so I can swap the SE mufflers in and out, for when I really want to raise hell....

[JSRS6]

1. Try to reuse the clamps between the main cats and the resonators. Have the shop make a clean cut before the main cats where the pipe is straight. Then use the clamps and new piping. A lot of shops will just spread the end of the pipe, slip it over, and weld it.
2. There have been numerous testimonials on here and rs246 regarding the non res. Youtube mooch and his old rs6. Its personal preference. My preference will be straight pipes all the way back to milltek tips. Once i get around to it.
3. You wont be doing anything for backpressure with the main cats and resonators. This mod will be ALMOST purely for sound. You MIGHT get a few hp out of removing the mains. Nominal at best.
4. Good idea about the removable mufflers, might incorporate that into my straight pipe idea, or install dump valves or something if i need to be quiet...

[kismetcapitan]

damn, it's a pity that all the backpressure is in those damned downpipes, and that they're so hard to get to, and carry some risk in snapping studs...

I definitely will have them use all stock clamp connections, so that my exhaust remains modular. And because the last section is fairly short, one can have straight pipes made, and store away the mufflers. Swapping them back and forth would be easy enough that dump valves would probably not be worth it. My issue with DVs...where are they going to dump to?

[JSRS6]

True, would a lot more cost effective to have a couple short pieces made with hangers to go in place of the mufflers when desired. Local Indy shop installed one on an m5, right around the rear diff area where the two pipes go in different directions. Sounded WICKED! Just a thought.

[Spidercat]

Here's what you need if you decide to keep the secodary O2 sensors:

www.034motorsport.com/fabrication-exhaust-plumbing-o2-sensor-spacer-banjo-style-ultra-low-profile-p-20198.html

I can't actually check this link from work due to security blocks, but I believe these are what I have.
Go to 034 Motorsports and search O2 sensor spacers. You'll obviously need two. They are ~$42 each and function by taking the secondary O2 sensors out of the direct stream of higher airflow. When I had my main cats replaced by straight pipes and electric dump valves, I was getting secondary O2 lamda sensor codes about once/month without the spacers. Post-spacers, about q 6 months. I just delete the codes, but CELs are always a little unnerving.
Or you could just adjust your tuning program and code them out, I guess. I'm very satisfied w/my tune, so I went this route.

[Spidercat]

Doh! Sorry!
These are what I bought:

http://store.42draftdesigns.com/O2-S...cer_p_306.html

Really nice quality. They do nice work.

[4everRS]

These look very nice Spidercat - good find.

Doh! Sorry!
These are what I bought:

http://store.42draftdesigns.com/O2-S...cer_p_306.html

Really nice quality. They do nice work.

kisme, if you or anyone else decide to remove the resonators, I would love to get your feedback and maybe even post a video. I'm interested in getting a little more sound, but not too loud.

[na1mt]

I am picking car back up tomorrow.....catless downpipes(stockers) with welded in test pipes and non resonated Milltek exhaust......I'll see if I can figure out how to post sound clips or vids. I have a short vid on cell phone that shop sent if you care to hear pm me yer cell number. Oh....and so far shop informs me no CEL

[kismetcapitan]

I am picking car back up tomorrow.....catless downpipes(stockers) with welded in test pipes and non resonated Milltek exhaust......I'll see if I can figure out how to post sound clips or vids. I have a short vid on cell phone that shop sent if you care to hear pm me yer cell number. Oh....and so far shop informs me no CEL

yes, do post up a vid, as well as your thoughts on noise levels when cruising on the highway!

Is there any benefit to keeping the O2 sensors, like improved fuel efficiency while cruising? When I map JDM cars, I don't bother with O2 closed-loop feedback mapping, and just map 100% open-loop, no O2 sensor inputs.