What is the purpose of the upper pipe that bridges the OEM mufflers together?

What is the purpose of the upper pipe that bridges the OEM mufflers together? Does it serve the purpose of an X/H pipe? I could have sworn I came across a thread of someone that cut the ends off the upper cross pipe a bit and installed a downward facing "T" pipe with an electronic exhaust valve. I can't seem to find that thread again though. I'm looking for a cheap way to get a bit exhaust sound without spending the ridiculous money the aftermarket companies charge for a catback which doesn't add meaningful, if any, power. I know can unbolt and slide the OEM joining pipe over to create an opening, but it's not a good sound, largely because of how the exhaust escapes through the small opening causing wheezing/raspy sound. https://cimg2.ibsrv.net/gimg/********.com-vbulletin/1220x767/muffler_photo_3c6a9a3a0f61a969c1e5c17d6cac9cb485a496b5.jpg

I think most people seem to call it a "balance tube" which definitley helps the exhaust sound "smoother". I opened up the gap by sliding the sleeve over on my Boxster S which did introduce a bit more exhaust roughness/rumble. Not long after this I was able to buy a complete headers/mufflers set from a local club member that had replaced his Cayman S setup for full Soul Exhaust (nice!). So I thought I would experiment... I noticed that with the gap opened up, I could hear a "fluffy" sound which I took to being the gaspulses firing at each other and then out the small gap. So I opened up the gap a bit more by chopping a few inches off one side and fitting a bit of a pipe bend so the pulses weren't firing at each other anymore. That removed much of the fluffiness I was hearing and so I thought I would finish the job. I hacked off even more, acquired a pair of shorter radius stainless bends, re-used the original clamps.. The factory tip in this last shot has been angled down so I could take the photo but was then pivoted back up into the normal position. You couldn't see the extra outlets as they were hidden by the bumper. I thought this setup sounded quite good (all subjective of course) and also allowed the exhaust to burble nicely when you got off the throttle. Interestingly, I have not yet transfered this setup to my Cayman, nor have I even opened up the top sleeve, it's all still stock. I still have the extra set of orignal mufflers that I was intending on DIY Carnewall modding...one day. Cheers, Julian KCMO

Op, search P9 for FREE EXHAUST MOD. or similar words. This trick on the 987 has been discussed many times over the years. I tried it but decided to instead get a Fabspeed sport exhaust catback.

Yeah, the free exhaust mod is the one where you slide the bridge pipe over and basically create a gap with the two pipes firing at each other. I've already done that and as Apexhunter987 noted, it creates raspyness, roughness, and rumble. This is likely due to the exhaust gases smashing into each while also escaping and catching the edge of the piping as well as the sound bouncing all over the muffler area/cavity.

Yep, I remember driving your Boxster last year and noting that it sounded pretty dang good, but also a bit loud inside (not super loud) and then you showing me your exhaust mod. I'm thinking about doing something similar by getting an exhaust "T" pipe to bridge the two mufflers together and aiming it downwards and back a bit to clear the exhaust tip assembly and then connecting a slash cut pipe horizontal to the ground so that the passing air helps pull the exhaust out. Aiming the tip down to the ground may also help at keep some of the exhaust resonance at bay rather than aiming it to the bumper area cavity. If it sounds decent, then I'd consider adding a electronic exhaust valve so I can reduce the volume on longer drives. Or maybe I'll just buy a used 987.2 OEM exhaust, borrow your welder, and mod the exhaust like Carnewal does

The free mod can give you some drone on the highway. Especially at 2k with PDK . But it does sound really good. Combining the free mod with carnewal or PSE is also a lot of fun but can be droney as well.

Too bad the Fister mod is not available on our 987s. Did it on my 996 and produced a nice exhaust note, no drone, not too loud, with small burbles on pedal let-off. And for around $600.

Getting back to the original question, generally a tube like that allows exhaust firing pressure pulses to "communicate" between both halves of the engine. Just an educated guess.

It isn't? Odd - my '09 has it. Former owner put it on. He included the stock exhaust when I bought the car, I never had any desire to reinstall the stock system, so I sold it. The Fister does make a very nice noise with the top down, especially in underpasses and tunnels. Very nice noise. And burbles not pops (pops are much too JDM for me..)