Radical G37 Coupe Muffler Experiment (with Pics)
 

So I wanted to experiment with the OEM muffler that comes with our G37 Coupe. I’ve always loved the sound of it, just wanted to increase the volume a bit so we can hear it in the cabin. This is the main purpose of this experiment.

Couple of Disclaimers:

• I don’t care about weight savings by going to a straight pipe and eliminating the muffler. I want to keep the “stock look”
• I'm not too concerned about back-pressure increases (within reason) even though the final solution is not increasing back-pressure (see explanation below)
• I don’t care about potential horse power gains by going with one muffler over another (I've tried axle-backs and did not like any of them)
• I don’t care about “wasting” a few bucks trying to find a way to make this exhaust louder (see pricing below).
• This was just a science experiment that I’ve always wanted to try with this car.

Stage 0: “Exposing the OEM Muffler in all its glory”
The following pictures shows the internal components and chambers of the G37 coupe’s muffler. The first picture is one that I found on this forum and the remaining few pictures where from my own muffler.
https://cimg5.ibsrv.net/gimg/www.myg...47793a98e5.jpg
Fully exposed internals in all its glory. Notice the Helmholtz tube (at bottom of pic) that’s used to cancel out certain frequencies and spans both internal chambers
https://cimg7.ibsrv.net/gimg/www.myg...b96a257ffd.jpg


My exhaust: Incoming exhaust flows from the TOP and enters the internal chamber to the right.
https://cimg1.ibsrv.net/gimg/www.myg...25a57d1fe2.jpg
Opposite side of the incoming exhaust. Notice how the perforations are different. They are polar opposite of the left side. Must have an effect on the sound

What I did from here is I went through 4 distinct stages and separate trips to the muffler shop (R&J Welding in Apex, NC) to try to come up with a sound that I liked. The four stages where:

1. Stage 1: “No More J-shape tube”
2. Stage 2: “Flush cutting the Outlet Piping”
3. Stage 3: “Close off the internal Chambers”
4. Stage 4: “Enough of this, just straight pipe it!”

Stage 1: “No-More J-shape tube”

I figured the most obvious thing to do was to eliminate the J-shape pipe coming from the incoming exhaust to the internal echo chamber. Figuring this would increase the volume a bit so off to R&J Welding I went.

Result: Just a minor increase in loudness and it kept the G37 coupe original sound. I was not pleased with just the subtle increase in volume and I wanted more. Was initially thinking that this would dramatically increase the sound and possible drone, but it did NONE of that.

Cost: $40

https://cimg1.ibsrv.net/gimg/www.myg...95d13a6282.jpg
Exhaust gases enter from the bottom of this photo and to the left, however the J-Shape pipe was cut off.

Stage 2: “Flush cutting the Outlet Piping”

Went back to the welding shop after tearing open a donor muffler from @The Pope . @The Pope had one sitting around and figured having 2 mufflers will enable me to drive the car and experiment with the other one. Then I can swap them as I make changes to each of them.

I noticed the exhaust port had a 2" extension sticking out and was figuring that this could be not allowing some of the sound to escape so I had the muffler shop flush cut it.

Result: Was very surprised by this change. Using the muffler from @The Pope (his was from a 2014 Q60, mine is from my 2011 G37) it was actually quieter than the previous Stage-1. I wasn’t sure if it was due to being a newer muffler from the Q60, but it actually was quieter. So I took off the muffler damper (hard-rubber round knob hanging out on the driver side of the muffler) to see if that made a difference - nothing! So after talking to the techs, they suggested closing up the hole to the internal chambers. Onto Stage-3.

Cost: Another $40

https://cimg4.ibsrv.net/gimg/www.myg...b90f902268.jpg
In this photo, exhaust gases enter from the top and exit to the right. Notice the "near-flush-cut" on the exit port.

Stage 3: “Close off the internal Chambers”

This time we had the j-pipe cut out, the flush cut on the exhaust exit-port and now the tech closed up the big hole leading into the internal chambers. Note that the internal chamber has many perforated holes in it, so its not totally closed and the sounds will be canceled from the left to the right exhaust ports.

Result: Well, I was hoping "this was it" but it only increased the sound a little bit. At this point, I felt like my options were over. But the more I studied the picture, I figured I'd just go big and gut the internals as much as a I can. Onto Stage 4.

Cost: Another $40 (see the pattern? :-) )

https://cimg6.ibsrv.net/gimg/www.myg...b01bfdd105.jpg
Internal chamber flush cut

https://cimg8.ibsrv.net/gimg/www.myg...6819c1c2af.jpg
Internal chamber covered up.

Stage 4: “Enough of this, just straight pipe it!”

I made V-cuts into the internal chamber to open up the entire muffler as best as I could. So I brought it back down to the muffler shop. The tech later texted me with an idea which was to just place 2 90-degree pipes back to back and connect the exhaust input to the exhaust output. I was worried about the reducing of the pipe diameters but if you look closely at the pictures, each of the incoming exhaust and outgoing exhaust pipes are already reduced, so I said - why not? See the picture below to see how he was able to fit the intake to the exhaust ports (photo shows a semi-finished double 90-degree bend prior to welding it together).

Results: Well I gotta say, it sounds pretty damn good. Warm startup is not any different than before. Cold startup is definitely louder but not obnoxious. Normal driving mode is no different than stock, but when I get on it, it comes alive. However the refined, baritone sound of OEM G37 coupe exhaust is not there (all of the noise canceling is probably gone). There is more of a bass sound coming from the exhaust plus it’s a louder. I can finally hear it in the cabin and the wife said - "oh yeah - its definitely louder outside of the car". Also, there is no drone whatsoever.

This car now has a split personality that comes alive when you want it, but is mellow when you don't. So I'd recommend giving this a try if you don't want to spend a lot of an aftermarket setup.

Cost: $60 - I asked if they needed more, but they said nope, $60 is enough. Tech gets $20 tip (plus other tips along the way).

Total Cost of this experiment:

• $50 for OEM Muffler +
• $180 muffler shop
• Total Cost = $230 (but if you are interested in trying this, I just saved you $170 - you can thank me ;-) )

https://cimg3.ibsrv.net/gimg/www.myg...e846ea006b.jpg
Spot fitting the bends to get it just right.

https://cimg8.ibsrv.net/gimg/www.myg...3e1a3381c5.jpg
This is a key photo. See how the original OEM muffler was reduced on the incoming of the exhaust gases? Seeing this, I wasn't too worried about a slight reduction in pipe diameters to make this work. Its the same same as the OEM pipe.

Cold Startup. Finally got around to doing one before the morning workout. I think it sounds great, quiets down. One of these days I'll try to get a drive-off video (been too busy this time of year).

Hope you enjoyed this fun experiment. Would recommend it to those that 1) wants to save some cash but 2) wants to increase the level of sound from their coupes.

Wow, thanks for the pics! The OEM coupe muffler is extremely advanced.
Years ago I put a VQ35DE into an old Maxima and I so badly wanted the G35 coupe sound. I tried many different mufflers, this explains why I couldn't get the "coupe" sound from off-the-shelf mufflers.

The sound of the stock coupe exhaust is so perfect I don't get why people even bother "upgrading" to aftermarket exhausts. But, then again, I don't "get" why people like their rim lips to stick out past the tire sidewall and fenders.....

Stock sound is nowhere near perfect but to each his own.

Stock sound is perfect, but to each their own. :thewave:

If someone can get the G37 to sound like the G35, count me in!

If someone could make the VQ sound like a straight-six, I'd be all over that like white on rice.

Congrats to the OP for having a sound (pun very much intended) idea and a vision for achieving it and the persistence to experiment until he found what he wanted. Thanks for the photography, I never expected the OEM muffler to have no batting inside.

Based on what I learned, I think the BEST possible option to make the G37 sound like the G35 is this.

Go the straight-pipe route (stage #4) but instead of using solid pipes, use perforated 90-degree pipes. That way sound can escape quickly but sound also makes it way into the internal-chambers to create the sound. That's what I'd try (may still do that, but need to find another donor muffler to achieve this).

so swapping a G35 catback exhaust onto a G37 and modifying to fit won't do it?

Is the sound only unique to the vq35? I highly doubt it since the Nissan Altima has the same motor but sounds nothing like the G35.

My friend has a G35 coupe, it sounds exactly the same as my Q60 (G37) but seems more "pronounced" or louder overall. The tone is exactly the same between the 2 cars.

The reason the Altima V6 doesn't sound like the G coupe is the same reason the G sedan doesn't sound the same. It's also why I could never get my VQ35 powered Maxima to sound like a G coupe. This muffler design on the coupes is unique. The VQ35 cars with a spare tire wells need basic mufflers. The coupe forgoes trunk space in favor of a complex, transverse muffler, and voila, we have a difficult to replicate sound.

When I research aftermarket exhausts for the coupe, I get drawn to models like Ark Grip and HKS Hi-Power, and they have the Helmholtz resonator similar to the OEM coupe muffler (only diff is external/internal).