So who has Milltek downpipes and catbacks installed?
12-27-2006, 04:29 PM
#1
AudiWorld Super User
Thread Starter
So who has Milltek downpipes and catbacks installed?
I'd like to hear impressions for those who have both the resonated and non-resonated catbacks with the downpipes installed. I take the performance increase as a given. What I'd like to hear are impressions of cockpit noise for the downpipes with both res and non-res catbacks. I already have 10K miles on my RS4, spend quite a bit of time in the seat traveling, and would be interested in the cockpit noise during normal cruising. I could care less if the sound is overwhelming under full throttle. It damn well should be. I'm more interested in whether downpipes and non-res makes sense on all day trips.
I've done a bit of research on the RS4 exhaust, and Audi did a nice job on the header designs. Instead of the forged header/collector on the S4 V8, they did the job right and designed a pretty decent tri-y 4-2-1 design on the RS4. There are some compromises, because of space, but they did a neet job of doing a high-flow design, with good port-to-port isolation. Too bad we didn't get the R8 design, though. There they had additonal room to do an even better matched design, that's how they peaked the low end torque on the R8 a bit.
With the header design that we have the engine will definitely feel all of the benefit of good exhaust system, like Kimbo's dyno plots showed.
I've done a bit of research on the RS4 exhaust, and Audi did a nice job on the header designs. Instead of the forged header/collector on the S4 V8, they did the job right and designed a pretty decent tri-y 4-2-1 design on the RS4. There are some compromises, because of space, but they did a neet job of doing a high-flow design, with good port-to-port isolation. Too bad we didn't get the R8 design, though. There they had additonal room to do an even better matched design, that's how they peaked the low end torque on the R8 a bit.
With the header design that we have the engine will definitely feel all of the benefit of good exhaust system, like Kimbo's dyno plots showed.
12-27-2006, 04:59 PM
#4
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Der Kimbo posted dyno results back in Nov. +20.4 whp and + 20.7 lb-ft torque...
check out:<ul><li><a href="https://forums.audiworld.com/rs4b7/msgs/29029.phtml">https://forums.audiworld.com/rs4b7/msgs/29029.phtml</a</li></ul>
12-28-2006, 03:43 AM
#5
That was for non-resonated/non-valved I *think*.......
I wonder how much for the others? My main concern is sound. Loud at cruise is just no longer acceptable to my aging ears.
12-28-2006, 06:13 AM
#7
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Here's a quote from jetjammer
"As far as performance, I felt an improvement from the catbacks alone. After the downpipes, OMFG! I feel a significant difference. She's always been fast but she feels much quicker now. I haven't had enough stick time to tell where she pulling now. It definately DOES NOT feel like there is any low end torque loss. For those of you who've driven or know what a difference the S4 stock vs. S4 w/Milltek fullback is, this feels umpteen times better."
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12-28-2006, 06:19 AM
#8
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Thread Starter
My comments
After looking at the design of the RS4 headers and the Milltek downpipes, I would expect the following:
1) The RS4 header is designed to empty into high flow pipes without obstructions. This is a much different design than the S4 V8 header, and will have significant performance implications. Whereas the S4 header will get "squirrelly" with various configurations of downpipes and catbacks, due to significant port-to-port back pressure in the header itself, the RS4 header is specifically designed to flow into an exhaust system with low back pressure. In the case of the RS4 header design, exhaust system back pressure is not your friend.
2) The stock downpipes place two cats in the flow path, one at the upstream side of the pipe and the other at the downstream side. On the Milltek downpipes, the cat has been placed on the downstream side only. This causes a longer path length from the exhaust port to the 1st obstruction, which is the hi-flow cat. That longer length should, in my opinion, open up the bottom end to mid-range torque even more.
3) With this header design, anything that reduces obstruction and reduces flow restrictions should help performance: high-flow cats, larger bore pipes, low flow silencers.
1) The RS4 header is designed to empty into high flow pipes without obstructions. This is a much different design than the S4 V8 header, and will have significant performance implications. Whereas the S4 header will get "squirrelly" with various configurations of downpipes and catbacks, due to significant port-to-port back pressure in the header itself, the RS4 header is specifically designed to flow into an exhaust system with low back pressure. In the case of the RS4 header design, exhaust system back pressure is not your friend.
2) The stock downpipes place two cats in the flow path, one at the upstream side of the pipe and the other at the downstream side. On the Milltek downpipes, the cat has been placed on the downstream side only. This causes a longer path length from the exhaust port to the 1st obstruction, which is the hi-flow cat. That longer length should, in my opinion, open up the bottom end to mid-range torque even more.
3) With this header design, anything that reduces obstruction and reduces flow restrictions should help performance: high-flow cats, larger bore pipes, low flow silencers.
12-28-2006, 07:36 AM
#10
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Design differences in S4 vs. RS4 headers
All of these pictures come from the Bentley Manual.
This first picture shows the S4 V8 header. This is a cast assembly, typical of many auto exhaust headers. It's easy to manufacture, but not especially high performance, since all exhaust ports empty into a common chamber. This causes exhaust port interference and exhaust gas to flow into neighboring combustion chambers. The ultimate limit to flow performance is this header. Cylinders 1 and 6 get hit with some nasty backpressure from neighboring cylinders 2 and 8, which cannot be fixed by any downpipe or catback system.
<img src="http://www.teraspeed.com/RS4/s4_header.jpg">
The second picture shows the RS4 header on the left engine side. The configuration is a double Y 4-2-1. This type of design pairs exhaust ports that are maximally seperated in exhaust valve opening, to ensure their independence.
<img src="http://www.teraspeed.com/RS4/rs4_left_header.jpg">
The third picture shows the right side header. Notice that that Y has been changed to different port branches from those on the left side. This is a consequence of the V8 firing and exhaust valve opening order. To keep the exhaust ports maximally separated the header Y ports need to be swizzled.
<img src="http://www.teraspeed.com/RS4/rs4_right_header.jpg">
This fourth picture shows the complete RS4 header assembly. You'll notice that the the 2nd Y is not formed until the downpipe flange. This is a classic "independence" design, where exhaust is delivered independently from each port down to the flange, before being allowed to travel back up to adjacent ports. At the downpipe flange, it is expected that there is larger bore pipe, with lower restrictions than the individual header pipes. If this is the case, then the majority of the exhaust wave (pulse) will travel downstream, and little will flow back up to other exhaust ports.
<img src="http://www.teraspeed.com/RS4/rs4_complete_header.jpg">
Nuff said?
For those interested, here's a picture of the R8 header, which was even further optimized
<img src="http://www.teraspeed.com/RS4/r8_header.jpg">
This first picture shows the S4 V8 header. This is a cast assembly, typical of many auto exhaust headers. It's easy to manufacture, but not especially high performance, since all exhaust ports empty into a common chamber. This causes exhaust port interference and exhaust gas to flow into neighboring combustion chambers. The ultimate limit to flow performance is this header. Cylinders 1 and 6 get hit with some nasty backpressure from neighboring cylinders 2 and 8, which cannot be fixed by any downpipe or catback system.
<img src="http://www.teraspeed.com/RS4/s4_header.jpg">
The second picture shows the RS4 header on the left engine side. The configuration is a double Y 4-2-1. This type of design pairs exhaust ports that are maximally seperated in exhaust valve opening, to ensure their independence.
<img src="http://www.teraspeed.com/RS4/rs4_left_header.jpg">
The third picture shows the right side header. Notice that that Y has been changed to different port branches from those on the left side. This is a consequence of the V8 firing and exhaust valve opening order. To keep the exhaust ports maximally separated the header Y ports need to be swizzled.
<img src="http://www.teraspeed.com/RS4/rs4_right_header.jpg">
This fourth picture shows the complete RS4 header assembly. You'll notice that the the 2nd Y is not formed until the downpipe flange. This is a classic "independence" design, where exhaust is delivered independently from each port down to the flange, before being allowed to travel back up to adjacent ports. At the downpipe flange, it is expected that there is larger bore pipe, with lower restrictions than the individual header pipes. If this is the case, then the majority of the exhaust wave (pulse) will travel downstream, and little will flow back up to other exhaust ports.
<img src="http://www.teraspeed.com/RS4/rs4_complete_header.jpg">
Nuff said?
For those interested, here's a picture of the R8 header, which was even further optimized
<img src="http://www.teraspeed.com/RS4/r8_header.jpg">
