[s-cars] Downpipe & Stromung exhaust for 95.5 S6

Postupack, Jeff Jeff.Postupack at analog.com
Thu Jun 24 09:20:33 EDT 2004

Hi Robert:

 I have the dubious reputation of being the Stromung guy, having organized many GP's for this system.  I can tell you alot based on personal experience. 
There are four generations of Stromung. The latest, Gen 4, provides the best audio qualities. I think it is fair to say the sound levels are flat through the rev range, with no boominess in the cabin. See below. You need to ride in a car with Gen4 to get the correct perception of how it sounds today. 
For most RS2 class owners, it is a great product at a great price. Guys in Colorado have taken custom designs further and into 3.5".
Welds: There were 3 instances I know of where the DP welds fatiqued. One was the RED RS2 modifed S4 Bruce M owned. He was racing it, and used it heavily. Stromung told us under racing conditions the DP should be changed after 2 seasons use.
The other 2 intstances were early versions of the RSS DP, now in production. In both cases 
the wastegate pipe broke where the weld attached to the DP tube. Stromung replaced the DP for free. A brace and gusset was added to support the wastegate. I have not heard of any more instances.
Clearance: Yes I agree the OEM system is tightest to the chassis. On my 1003 S4 with H&R and Bilstiens, I do not scrape the muffler system. other experiences vary widely and depend upon the installation and hangers that support it. 
Jeff Posto 
Historical information. I'm writing this from memory in an airport, and later can supply component parts numbers to clarify what's what. I think this is ture below.

I'll refer to the original Stromung built, TAP sold system as Gen 0.
(Stromung is now at Gen 4)
Gen 0 had no resonator, and the muffler was Magnaflow. IT did have a Cat. But was freakin' loud. 

Gen 1, was the first time I stepped in to organize the GP's circa 2001.

Stromung simply inserted a tubular resonator, which did nothing for sound attenuation.
This piped into the same MAgnaflow muffler as Gen 0, and I believe this was a 2.5" OD muffler inlet.
THe stainless piped necked down to that OD. Since this was so loud, Ralph P's kids labeled it the Boom Car, and Stromung gave us free magnaflow resonators to quiet the beast.

Not good. 
Gen 2 added the Magnaflow resonator standard, did not change the muffler so now (circa early 2002) I think Mike's observation remains true at the muffler inlet.

Gen 3 changed a lot of things: (Circa Fall 2002) 
We had to make it quiet, because it woke the babies living next to the Don. 
The rear muffler was made custom and large as the cavity could accommodate, and Stromung made that muffler inlet 3" OD. They also imporved the straight shot flow from downpipe exit to tail. Plus they used this new resonator that was larger and provided more clearance. 

I think Gen 3 and Gen 4 now are 3" OD, from the 2.5 inch to 3 inch transition point at the downpipe. 
Stromung nailed the sound qualities once and for all. A deep rich tone at idle with no boomy cabin noise. At WOT, yes it roars. 

Gen 4: Goal to improve the DP.
Stromung found the labor high to make a full 3" from the turbo flange, all the way back. 
The owner also talked to Corky Bell, who advised contrary to our wisdom.
COrky told Stromung that the turbo exhaust gases depart like a twisted rope, and his experience showed a DP built with an (motocorss term) expansion zone would allow it to escape quickly and unwind. There 2 points biased the design of the RSS DP.

Gen 4 Stromung  moved the wastegate tube entry downstream, and added stainless flanges at the roadside. Added a 2nd bung for EGT. Turbo flange remained cold steel.

I think the actual vehicle testing MP did with a 3.5 inch DP does prove a lot more useful than all this theory.

Jeff Posto 

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