I've had this catback exhaust for 4 months now, and I'm ready to do something to quiet it down a bit and I need some advice from you guys.
- I love the power, especially low-end torque
-After Dynomatting the car, the sound still a bit loud, I enjoy it at times and hate it when I have guests in the car

What if I change out the resonators? Is this possible, and how would it affect performance?

Has anyone had any success with modify the Stillen Exhaust?

 

You could try changing out the resonators for longer ones like Magnaflows but I doubt if it will significantly quiet down the sound level. Or you could try adding two more additional small resonators after the other two if at all possible. Good luck as I don't think anyone has attempted to do what you are seeking. You're pretty much going to be experimenting.

04' G35S 6MT Ivory Pearl, Willow, Premium
Z-Tube / NFC Y-Pipe / Custom Mid-Pipe / 350 EVO Rear Sway

 

I hear twin-turbos will quiet-down an exhaust with aplomb...

'03 G35s 5AT, Garnet Fire/Willow
Staggered 18" SSR GT1/Bridgestone PP S03
Eibach Springs/Sways, Stillen 2-pc BBK
Stillen Intake & SS Cat-Back Dual Exhaust

 

Gotchaa,

I had the same experience... After a while the fun wears off and it gets to be too loud.

I went underneath the car to investigate the exhaust system by tapping on all the various exhaust system parts with a small stick. I was looking for any part of the exhaust system that would resonate excessivly. The intensity of sound pressure generated by a running engine will be enough to acoustically excite any metal part if that part is willing to ring or resonate. Tapping with a stick will identify all these same parts without the engine running.

I noticed the dual stainless tubing does have a tendancy to ring. Fortunatly a nice exhaust heat wrap should damp much of the metal tube ringing.

But much worse than the tubing, I noticed the very thin sheet metal used to make the muffler is a big time ringer/flapper. And a nasty one at that. Because the muffler has two flat panels on the top and botttom, with rounded sides, the flat panels will flap/vibrate madly from the intense pressure waves pulsing within the muffler. These flat panels add a whole lot to the sound you hear comming from your car. But it's not the sound you want. The thin flimsy sheet steel being pinged by the pulsing exhaust flow sounds makes it sound like a metal trash can. These thin metal flaper panels need to be damped.

Here was my solution. I won't necessarily say everybody can do this because I have a small machine shop in my garage, but I reduced the sound dramatically. I cut two pieces of stainless sheet metal to the same size as the flat metal panels on the muffler.
I then went to home depot and purchased fiberglass cloth to work as a damping material. I folded several layers of the fiberglass cloth to form a (~3/16") pad of only slightly smaller area than the mufflers vibrating panels. I took the muffler off the car, laid the glass pad on top of the vibrating panels, put my stainless sheet metal on top, smushed it firmly against the panel and TIG welded it into place. I did this on both the top and bottom of the muffler.

The result is probably ~6db less sound and the quality of sound is much improved. It's still loud, but it got rid of the harshness generated by the metal flapers.

I originally intended to document the entire procedure but then figured it wouldn't be of much help to the average forum member. As I mentioned above, my garage is a small machine shop and I don't expect others to have the tools necessary to do this sort of thing.

Anyways, I put the mufler mod to the test. I went to work with my carpool budy and asked him if he noticed anything different about the car. ( I didn't tell him anything about a custom muffler mod.) He said "It's quieter... what did you do to it?" I felt it was quieter, but at that point I knew the mod worked. My carpool budy picked it out without me hinting anything. My wife also commented that it is quieter.

Good Luck!!!!

In Theory, practice and theory are the same.
In Practice, practice and theory are not the same.

2004 G35 6MT Blk/Blk Sedan Stillen Air, Stillen Exhaust

318865-Muffler a.jpg

 

One more shot.

In Theory, practice and theory are the same.
In Practice, practice and theory are not the same.

2004 G35 6MT Blk/Blk Sedan Stillen Air, Stillen Exhaust

318866-Muffler b.jpg

 

Hydra...

I've got access to a TIG welder...so i was wondering if you might be willing to cut the metal for me? Also, what do you think about using the "accumat for under the hood" instead of the fiberglass?

Lemme' know.. I'll pay ya for your work and parts if you like.... cheers, ted


'03.5 Sedan 5a: BS/G, Prem, Aero/Body, Sport, Nav
Click for MODS - www.teamtransport.org

 

SoCal,
It shouldn't be a problem, I have enough material. I'll see if I can bang out a couple of them this afternoon. PM a adress to send it to. I'll ask my wife if she could UPS them Monday or Tuesday.

"Accumat"???... I'm not familiar with it. If it is more dense than folded glass cloth that would be good. Dense is good. What ever the damping material is, it should be good to at least 1000'F.

About 20 seconds after a 1/4 mile uphill sprint, I measured muffler internals (up the muffler tip end) with a laser pointer pyrometer @ 530'F. Temperature was falling rapidly while measuring!




In Theory, practice and theory are the same.
In Practice, practice and theory are not the same.

2004 G35 6MT Blk/Blk Sedan Stillen Air, Stillen Exhaust