October 03, 2004

Review: Stratmosphere Milltek Cat-back Exhaust
Text and Media, Don Pavlik

The B6 S4 comes equipped with a V8 stuffed under the hood. Hit the key and it will fire up and settle down to a quiet burble. There's no mistaking the exhaust note as a V8 but from inside when underway it's barely audible over road noise. For a performance car the factory exhaust is quiet and, for many, potentially a waste of perfectly good V8 music.  

Enter the Stratmosphere Milltek dual exhaust. The Milltek is a dual cat-back system that is available in two flavors, resonated and non-resonated. The resonated system is a step up in sound level/sound quality and performance over the factory exhaust. The non-resonated is yet another notch louder. Both versions will be louder still if you choose to run the Milltek downpipes Stratmosphere also offers. 

I tested the resonated system with stock downpipes and it turns the muted S4 into one with the presence befitting a performance sedan. The burble at idle is smooth, deep and will surely put a smile on anyone who likes the sound of a purring V8. Select a gear and move off swiftly and you're treated with excellent V8 sounds--deep, with quality harmonics that turn into a V8 wail as the tach swings to 7,000 RPM. It isn't a boomy or harsh sounding exhaust by any means. With the tach still up the rev range back off the throttle and, again you're rewarded with well tuned sounds as the V8 rumbles down the RPM range against it's own compression. Mmmmm. So sweet. 

In daily driving, the Milltek exhaust note makes it's way into the cabin but it's not so loud that it becomes overbearing. With the factory exhaust on my Tip equipped car, if I drive in a docile manner the exhaust note is nearly inaudible and I can't really hear the exhaust note differ on gear changes. With the resonated Milltek the exhaust is loud enough that I was able to hear the exhaust note change on lazy upshifts. The exhaust note is present as a low background rumble at engine speeds below, say, 2,100 RPM and it mellows out to a purr as the revs increase. The added exhaust feedback would certainly be a plus for drivers with a manual transmission who want to shift by ear rather than by the tach. 

Exhaust Comparison - 2:31 (mpeg, 6.68MB)

Note: you will need good speakers or a subwoofer 
to hear the full tone of the exhaust systems

I'm one to prefer a silent exhaust (read: stealth) and I found the exhaust a smidge too loud for my taste from time to time (like when in parking garages) and sometimes I preferred the silent nature of the stock exhaust when puttering along in slow traffic. That said, I'm usually the exception to the rule on exhaust noise so consider where you fall on the scale of exhaust noise when weighing my comments. Stratmosphere first released the resonated version and after customer feedback released the non-resonated version because many customers thought the resonated was still to quiet. Stratmosphere offers both so the choice is yours. 

Sound level measurements revealed that overall peak sound pressure readings (SPL) are indeed a bit higher. Remember that a 3dB change in SPL means twice the sound energy. Exterior readings were taken with a meter placed on the vehicle centerline 15' from the rear of the vehicle. 

The stock exhaust on early 2004 US-spec cars include flaps in the muffler pipes that are supposed to reduce exhaust noise by closing a valve above 1900 RPM and routing the exhaust differently through the muffler. My measurements didn't yield any difference with the flap system disabled nor was I able to hear a difference in loudness or the sound (tone) of the exhaust. Go figure. 

Exhaust Noise Measurements
  Stock Milltek
Exterior idle 85dB 86.5dB
Interior idle 70dB 71dB
Exterior full throttle departure 91dB 93dB

The Milltek is an all stainless steel system with a near-mirror finish on the stainless steel mufflers. Exhaust construction is very good with all mandrel bent bends. Weld quality is clean. It uses factory exhaust hanging points and the exhaust hangers look very well made and quite substantial. The exhaust comes in 7 pieces comprised of 2 mufflers, 2 tips, 2 resonators and an H-pipe. The well crafted exhaust tips are available in your choice of 90mm and 100mm. All clamps are supplied as are instructions, latex gloves, zip ties and exhaust paste to ensure a no-fuss, leak-free installation.  

Installation was a quick and painless ordeal that took about 45 minutes (performed on a lift). Fitment was spot on. It's tucked up under the car nice and tight so no worries about snagging low hanging bits if you happen to have suspension that lowers the car. I didn't experience any problems with it contacting anything under the car although it does come close the fuel evaporation line on the right side of the spare tire well. The supplied documentation discusses the fuel evaporation line and includes additional ties for the line to ensure you maintain proper clearance. The 100mm tips on my sample exhaust filled out the lower valance cut-outs perfectly. Installation-wise it just doesn't get any better than this.

Enough of this fluff you say... what about performance? Stratmosphere claims dyno numbers of 15 hp and 20 lb-ft of torque at the wheels. My own testing with accelerometer based measurement equipment yielded an "on the road" gain of 8 hp over stock. Given that my data is affected by rolling resistance and aerodynamic drag I'd say Stratmosphere's dyno numbers are pretty much on the money.

Stratmosphere also offers manifold back downpipes to complement the cat-back system. Downpipe/cat-back combination yields claimed dyno numbers of 30 wheel hp over stock. Wow. 

The Stratmosphere Milltek cat-back exhaust is a fine exhaust indeed. It simply shines in all categories. It's well made, looks fantastic and has perfect, trouble-free fitment. Add that with bringing out the voice of the S4's willing V8 and wringing out extra power and you have a winner. You simply cannot go wrong with this exhaust. 

Stock Exhaust

Stratmosphere Milltek cat-back

Stratmosphere Milltek cat-back system: $1095

28 Boulder Creek Drive
Rush, NY 14543
Phone 585-533-1777
[email protected]

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