I have been driving for about a week with Stillen cat-back exhaust (along with JWT pop-charger and Z-tube). Well, the car is LIVELY, to say the least. It scares me - acceleration is VASTLY improved. I sort of raced an Audi S4 a couple of days ago, and kept catching up and tailing him any time he tried to get away. That was funny - the guy kept looking in his mirror with a confused "I have a V8!!!" look on his face.

But the problem is, at ~80mph in 5th gear - that's about 2500 rpm - there is a definite droning growl from the muffler. It gets annoying a little, but since I usually have music volume blasting at 23, I mostly don't hear it. Yes, photos to follow.

I have heard people say that Stillen cat-back will quiet down a little after it's "broken in" - well, how much is "a little" and how long does it take to beak in? Searched, but to no avail... Please help!

 

Believe it or not, my Stillen toned down alot AFTER I installed a Z-Tube. Since you already have it, the only difference is that I have the K/N in the stock box. Mine just seemed to tune out the drone with the Z-Tube. Almost like the resonances cancelled each other out. If you still have the stock airbox, get a K/N drop in and try it out. You will be surprised. Might even feel a little more torque gain with the stock box too.

 

i have a JWT pop-charger. i don't hear it over the exhaust. with the window open and stationary, i can hear whistle from the intake when revving the engine. but while driving, all i hear is exhaust. growl, very respectful, but still just a tad too loud... if i had a 6MT, i'd have an option of driving in 6th gear on the highway, and then my RPMs would be around 2300 at ~80mph... as it is, though, in 5th gear at ~80mph it's at around 3000 rpm (correction to my original post) and it's almost intrusive (when the music is off, that is )...

 

update: talked to Rob at zcargarage today - was there for a new Hotchkis sway bars install (speaking of which, need to update my sig ) - he drove the car and said that it does sound quite a bit louder than the same stillen cat-back they put on another G35 sedan. he called stillen, they said they'd get back to him about this... still keeping my fingers crossed...

 

another update: reset my ECU a couple of hours ago. got it on the second try, used instructions from technosquare as i couldn't find the FAQ thread on these forums.

the car seems to accelerate better, shift easier, and the exhaust...

well, IT'S NO LONGER LOUD! the volume cut down by about 30%... to say the least. it's objective, i know, but still. i drove it hard - accelerating hard all the way to mid-3rd gear.

there is still slight hesitation when beginning in 1st (manumatic) from around 2k to 4k rpm, then it takes off like it's on fire. still not too satisfactory, though - since i had crawford plenum installed friday, the idle is at 800rpm, and it used to be around 650. ECU reset did not help. will have the guys at zcargarage look at it monday morning, when i am there to fight for right-offset rims (see this thread for more info on that one).