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Discussion Starter · #1 ·
Haven't been on here in a while. Not that I posted that often to begin with. Anyway, looking to do a full exhaust on my '12 Advance in the next 6-9 months. Obviously going to do a long-tube J-pipe and high flow cat. We have to do annual emissions tests here so I'd like to keep it passable. I haven't done as much reading lately, so if I'm not mistaken, the long-tube J-pipe is only available from RV6, not ATLP (for the '10-13 models).


Beyond that, I'm probably going to have a shop in Kentucky do a mandrel-bent stainless catback. They've done a 3" stainless single on a '97 850 R for me in the past and their work is top notch. For sure removing the resonators completely.


My questions have more to do with the layout of the exhaust, post 3rd cat. The factory exhaust splits immediately after into 2-2.25" diameter piping (can't remember what my caliper said) and runs all the way out the back. I essentially have three options:

1) Have the custom exhaust split after 3rd cat;

2) Run a single exhaust over the rear axle, then a y-pipe and dual mufflers/tips; or

3) Run a true single to either side.


For cosmetic reasons, I prefer it to have dual tips because of the muffler cutouts on the rear bumper panel. Additionally, dual should be quieter. But whether or not it's kept single to the axle seems more based on the sound level as two resonators reduce noise more than one (in factory configuration) But I won't have resonators installed, so I feel like it might be easier and more economical to run a single pipe over the axle. Larger diameter to form the same internal area as two smaller pipes, but I haven't inspected the clearance over the rear axle, so I don't know if two smaller pipes fit easier than one large one. A single pipe with 41.4% larger diameter gives you double the volume, so if the factory exhaust piping is 2.125", a single 3" would provide the same flow as two 2.125" (that's based on outside diameter, so inside diameter differences could be slightly different). I also don't know if I should increase the overall flow rate, or keep it stock. If a slightly higher flow rate enhances the performance with the long tube J-pipe, I'd probably bite.


Rear of the axle, I'll be using straight-thru perforated mufflers, although I'd prefer to have cylindrical mufflers that run at a diagonal just after the axle, and have short piping to the tips, rather than the mufflers at the very rear with the massive tips on them. My 850 R had a black Apex'i N1 muffler with a 3" inlet and 4.5" tip, but I've found that most universal mufflers (that are standalone mufflers and not part of a system) aren't designed for in-line use with piping that extends beyond the muffler body itself. I'd really like to use components from a GReddy exhaust, but I've been looking around and the ISR exhausts sound really nice. Is it even considered acceptable to cut the 4" tips off the mufflers and weld in a 3" outlet to be used for the piping to the tips? I just really don't want two massive mufflers hanging below the rear bumper. I know Borla and other companies make the mufflers as standalone units to go someplace other than at the exhaust's exit, but I'm not a huge fan of the way they sound. I might use the factory exhaust tips for a sleeper look. Just haven't gotten that far. Technically I could have them split the exhaust after the 3rd cat and have the mufflers installed in place of the resonators and just run the piping to the tips, but I absolutely hate the way the resonators look sitting under the vehicle. Plus, I like the look of twin cylindrical mufflers branching away from each other behind the the rear axle.


So any input would be appreciated.
 

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What are you trying to accomplish by doing this?

If you're leaving all the cats and sensors in place (which you should) then I don't think you can "improve" performance. Remember, larger is not always better. At best, you could hope to "not make things worse". I doubt you'll be able to get any meaningful gains.
 

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Discussion Starter · #3 ·
What are you trying to accomplish by doing this?

If you're leaving all the cats and sensors in place (which you should) then I don't think you can "improve" performance. Remember, larger is not always better. At best, you could hope to "not make things worse". I doubt you'll be able to get any meaningful gains.
On the larger, I think you misunderstood. The point of a 3" (or similar) catback would be to only have to run a single pipe over the axle instead of two, being that I'm having it fabricated and replaced. The factory exhaust splits after the 3rd cat, so by only running a single pipe, the diameter would have to be larger to maintain the same flow rate. That said, a 3" single would be equivalent to dual 2.125", which may or may not be the exact diameter. If I remember, it's a 2" diameter, so total area would be 6.28 sq inches, based on outside diameter. A 2.83" single would give you the same area, based on outside diameter. But with mandrel bends, could go down to a 2.75" and probably get about the same flow rate. That idea is solely based on simplicity for the fabrication of the exhaust. I'd prefer to run it dual immediately post 3rd cat, but I consider my options.

The J-pipe is obviously for performance gains. Those have been dyno tested and get noticeable results. The rest of the exhaust is for sound. I like a good exhaust. I've already done some research on CAI/SRI and chip tuning, neither of which seems to give any gains (and a poorly done intake can hurt performance). But freeing up the exhaust is not going to make things worse, especially in the higher RPMs.
 

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Discussion Starter · #5 ·
While I no absolutely nothing about exhaust components, this video may be of interest to you- any question please ask board member 'NotaPilot' (haven't seen him post in quite a while...his last login was around January of 2016
).

http://www.mdxers.org/forums/74-second-generation-mdx-2007-2013/47116-atlp-j-pipe-07-09-mdx.html

The ATLP is the one I want, but that one is specific to 07-09 models. I could be mistaken, but I'm pretty sure the only long tube J pipes for the 10-13 is the RV6. Fortunately, that's one of the difficult components to replace if it's not already fabricated specifically for our vehicles. The rest is fairly straightforward. Thanks for the link.
 
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