I took the plunge this past weekend...
First, some comments/observations:
1) It's LOUD - definitely louder than I expected.
2) The install was straight-forward, but as mentioned by Samstag there were some alignment issues. Thanks Samstag for the high-temp. silicon idea. No leaks!
3) The welds and overall workmanship look to be first rate. The Stillen tips are just plain beautiful!
4) Gas mileage is gonna really go down. I just can't seem to resist pushing down more on the go-pedal!
5) The overall tone is very pleasing - just a bit on the loud side.
6) Looking at the Stillen flow path, I can see why there are likely (yet unproven) significant HP/TQ gains vs. stock. The X-pipe concept seems sound. I'm very sceptical about Borla's "H" pipe. The numbers reported so far seem to support these observations.
7) The Stillen muffler is substantially smaller than the stock unit. It seems that Stillen could easily have made the system more acceptable (noise-wise) by spending a bit more and making a larger muffler. I would have paid the diff. if it resulted in equivalent (or similar) HP/TQ gains with less noise.
8) I tried to quantify the noise increase. Using a Radio Shack SPL meter, tests cruising in 6th gear at 60,70,80 mph, A-weighting, slow response. Note: clearly at >3000 rpm the Stillen is MUCH louder than stock. That's not an issue for me. The real question is how much louder is it on a long trip, mostly freeway cruising at 70mph (in 6th, 2500 rpm). So... At 60 - no measureable difference (most of the noise component is wind/tire). At 70, +2dB. At 80, +4dB (75-76dB). That's pretty significant.
9) At least it doesn't sound "rice" (which I HATE). Well, my step-father said it sounds like a "Honda". Ok, maybe rice but about an octave LOWER. A really nice low-end grunt sound at partial throttle.
10) The wife's not convinced (it's her car). Then again, she said that she "left a few people in the dust" on her way to work this morning. OOPS - I see traffic school in her future... She let me drive it day 1 after the install (just to make sure it was OK - no leaks). I "surprised" a Boxter S on the way to work. He def. stomped on it too - actually his exhaust had a very similar tone - not quite as loud though.

Bottom line - I might be selling the Stillen, and going back to stock unless I can make the car a bit more "civilized" inside again (don't care what it sounds like outside)!

Next, some questions:
1) Everybody (regardless of exhaust type) seems to comment on a "break-in" period (up to 300-400 miles), after which the exhaust quiets down a bit (seems to be true for Borla, Fujitsubo, and Stillen). Can anyone explain this? Is it due to residue buildup, or purely perceptual (i.e. you just THINK it's getting quieter as you adapt)?
2) Hydrazine (and others) have described a substantial improvement by dynamatting the trunk. That sounds like a good solution. What areas need to be covered, and what type of material (also source + cost) were used?
3) Hydrazine describes a simple mod. to reduce the surface resonances coming from the Stillen muffler itself. Anybody else tried this?

2004.5 G35 Sedan | Garnet Fire + Willow | 6MT | Z-Tube

 

Now that I've had mine on for about 500 miles I have a few more observations that might help. First of all, you should recheck the fit and position of the muffler. After a couple days I looked at mine and the tips practically disappeared under the bumper. The whole system seems to have shifted forward for some reason, and I can't pull it back by hand. It was also being pulled up too high which caused it to rattle the bumper and even melt the plastic a little. I had to remove the forward hanger to get it lower, and also increased the bumper cutout with a dremel and sanding drum. The almost hidden tips are actually pretty cool since I like a "covert power" appearance. But definitely check that out before long.

As for loudness, it seems like it comes and goes on mine. There's a drone under a load around 2500 that seems to be caused by vibration more than exhaust. I just ordered 50' of exhaust wrap and some sound dampening material from www.fatmat.com for the trunk based on Hydrazine's recommendations. I'd like to do something for the muffler as he did but I'll probably save that for last. I think that with the vibrations taken out of the equation it will be a very nice system.

 

Hey man good to hear you like the power and stuff, but it sucks you dont like the sound :/ Give it a week or two, my Borla with test pipes was loud too but quieted down ALOT or maybe im just ude to it, if not i can trade you my borla for stillen!! Lemme know. Martin


Martin
2003.5 BS G35
Nismo Aero/Sport Package
Injen CAI
B+G Springs
ADR M-Classic 19's..

 

Not to sounds sales-y, but the HKS Sport Muffler would suit you perfectly. I did the HKS muff 3 weeks ago and I just added the Z-tube early this week. I absolutely love this combo!

Sounds great and the butt dyno feels more pull (especially at the top end after the Z-tube). I also installed a 350z engine cover (had to modify it to fit the crank fan on the sedan).

Entire setup feels great, sounds great and looks great.

I plan to write a full review on the HKS muff and post some pics later.

 

Wrk, that's cool that it sounds great and everything, but the pop charger prob gave you all of your gains!! The stock muffler isnt the restrictive part about the factory exhaust, its the cats and everything else, i think he wants gains and will not get that out of a muffler replacement but i could be wrong about what he wants.


Martin
2003.5 BS G35
Nismo Aero/Sport Package
Injen CAI
B+G Springs
ADR M-Classic 19's..

 

Here's the real skinny on exhaust systems for the G. You're not going to like it, but its the bottom line.

The problem with a cat back exhaust is that most of the restriction is in the exhaust valve itself, not the headers, the precats, the cats or the exhaust system. The farther from the restriction you try to improve things the more miniscule the gains are.

I totally agree with you that my gains with the HKS muff are probably zilch. That being said, the gains from replacing the CATs, Y-pipe etc. are going to be de minimus as well. The biggest "claim" I've heard of is 21 hp with the Stillen setup. Frankly, no one has corroborated this and things such as ambient temperature etc. can result in the swings in dyno reading that potentially could account for 60-70% of these so called "gains".

Point I am trying to make is that gains from exhaust systems for the G (even if they are $1000+ dollars, titanium etc.) are going to be minimal period.....of course those that have paid $1000+ plus for their systems are going to tell me I'm full of $hit....bring it on...reality is reality period.

My point to the original poster was that the tone and db he's looking for (I'm guessing based on this post) would be well served by an HKS+Z-tube combo.

I agree with you in that any so called increases that I'm perceiving are probably from the Z-tube.