G37s catback exhaust - finding the right balance

[regen]

I have a 2012 G37S, which I just bought after selling my 2005 G356MT which I drove for 162,000 miles over five years (150 round trip commute). I was so pleased with the durability, reliability, and fun-to-drive combination of the G35 that, when it came time to sell, I stayed in the G family.

I had always envied the sound of the G35 coupe and thought from time to time to do something with the G35 exhaust but never did. When I first drove my G37S, I was dismayed that it was as quiet as a tomb under all speeds no matter how deep into the throttle I got so I decided to look into options.

On this forum there are a number of posts dealing with cat-back exhaust mods. I followed one that recommended a Magnaflow 11385 as an X pipe to replace the two stock resonators and dual 12221 mufflers to replace the OE mufflers.

The first step I took was the 11385. I bought the part online from Autozone for $95 and had a local muffler shop install it. The job entailed the removal of the stock setup just aft of the cats, piping in true dual exhaust into the 11385, then connecting to the stock mufflers. The shop charged $285 for the piping and about 2 1/2 hours labor. I've seen others comment that the job shouldn't cost more than $100 but the pipes alone were $90 so I'm pretty sure I got a fair deal.

The result was a really pleasant growl on acceleration from about 15000 - 2500 RPM that wasn't there at all before. I rode with this for a couple of weeks, then decided to replace the OE mufflers with the 12221's. Autozone sent me a 20% off online coupon with free freight so I got both mufflers for $136. The installation was another $225.

I took the car from the muffler shop and started my 75 mile drive home, which takes me up and down many hills as I wind my way through central Virginia. Arrgh! The drone from the mufflers at 2500 RPM, or 65 MPH which is what I'm set at for most of the drive, was unbearable! It got much louder under load as I went up hills. When I got home and did some Google searches, I found that Magnaflow mufflers on many other cars have had the same problem (although this isn't just a Magnaflow issue, it applies to other after market mufflers). Some of the postings said the problem would get better after the mufflers brake in but I absolutely couldn't stand it so I had the shop reinstall the OE mufflers (another $125) and I'm quite happy now. When I told the shop guy about the posts that said the drone would get better over time, he said it would get louder but not so sure that equals better in this case. I've seen others comment in these forums that the same setup resulted in no drone so not sure what was different in my setup.

The lesson I'd like to pass along is, for me, the 11385 is a SWEET mod that gives me just the right mellow growl under acceleration but the sound doesn't intrude into the cabin at any other time. While the dual 12225 muffler mod was awful at 2000 - 2800 RPM, it did have a sweet rumble at idle that I enjoyed. Just thought I'd share my experience.

[kmckis1029]

so where there any noticable gains in performance? seems like you only concerned with the sound. after switching to an aftermarket intake on my G37x sedan, my exhaust note deepened and more sound from engine bay; but it's completely quiet on the highway at cruising speed (80mph for me).

[regen]

The cat-back upgrade certainly allows the G37 to breathe better at high RPM's, which should translate to minor performance improvement over say 5500 RPM. The stock setup takes two 2 inch pipes from the two catalytic converters, runs them through two resonators, then combines the exhaust stream to one point before expanding it to two pipes again before the dual exhaust. Think of the center point in an X. This pinch-point looks to be a 2 1/2 inch pipe. My new setup takes two 2 1/2 inch pipes from each of the cats to the Magnaflow 11385 which has two 2 1/2 inch inputs in and out then directly into the OE mufflers.

But your point is accurate, I did it more for the sound than the fury. I've had the G37S for about a month and I'm still surprised with the thrill of onramp merges, downshift-and-pass maneuvers, and 1-2-3 shifts with nice EEK's in 2 and 3. I did the exhaust modification because I was looking for some "ggha--ggggggha" to go along with the fun but only when I jumped on it. Towards that end, I am truly satisfied.

[audtatious]

So, how much did you eventually spend? For a budget I considered a used system but eventually went with the Invidia and other than one issue with a broken weld I've been quite satisfied.

[regen]

If I had just installed the 11385 and stopped, I'd have spent just under $400 all in. As it was, I spent an additional $475 putting on the 12225's then taking them off again. Ouch! (but I'm happy with how things ended up)

[audtatious]

Yeah, that's quite a bit more than I paid for the complete Invidia setup which is done very well.