If removing the rear muffler didn't make a difference, I might suspect that you have some exhaust restriction in the stock components (like a plugged cat as you suggested). Does the car make adequate power? Does it stumble, hesitate, or feel like it hits a power ceiling? Is there anyone local to you who has some experience with 928s who could tell you how your car is running? The later model cars are powerful enough even under less than ideal conditions that you might not appreciate the fact that you are missing power.

Just my 0.02

 

It doesn't feel any faster than my 4.5.

:|

 

Just a polite humorous query- have you had your hearing tested recently?

Assuming that is sound- if you want to use an X pipe and an RMB the practical solution is to modify the centre section. If you have the larger central resonator it will perform better than the later small one in that regard but doubtless is most likely going to be obnoxious socially.

The solution is to fit an after market muffler into the stock pipes. I used Bullet mufflers. We cut out the central resonator, tack welded the new mufflers in situ for alignment purposes and then had the assembly welded up by a local company who specialise in welding more exotic materials- SS was a breeze for them. The sound is awesome.

A while ago my wife was loading the shopping into her car at the local supermarket late one afternoon. Not too far away she heard heard the roar of a car accelerating hard up to expressway speed and said to my daughters "that sounds like your Dad's car" - it was!

A note of caution: if you do any welding like this in-situ on the car disconnect the battery earth lead and disconnect the LH/EZ leads while you do it.

Regards

Fred R

 

Guy goes to see the Dr and says:
"Doc, Ive been having a problem with silent gas. In the elevetor coming up here I had several episodes of silent gas, and sitting in your reception area I kept having silent gas, and even sitting here now I just had several eposodes of silent gas"
Doc says:
"Well, first thing we are gonna check is your hearing."

 

The exaust note is really a musical insturment and what sounds good is often hard to predict... it is however quite easy to make a 928 sound like an old 65 Chevy truck with a rotted out exhaust....there is NOTHING unique about the 928 firing order and it has a very typical V-8 sound.

 

I have an '98 S4 with Ott X-pipe, RT cats, Dynomax 14" mufflers, and 2-1/2" tailpipes out to rear. And DRONE at about 2200 RPM.

I've been doing a little web browsing this morning and found a thread (below) that describes some success that the Mustang folks have had in eliminating drone by adding ~24" resonance tubes teed off of the exhaust. There are some good links to exhaust and resonance control theory scattered among the three or so years of posts.

http://forums.corral.net/forums/gene...tely-gone.html

A rough measurement of my tailpipe lengths from the X-pipe to the tip is 8 ft 3 inches for the drivers side and 9 ft 3 inches for the passenger side. I assumed that the 8-cylinder effect starts at the X-pipe and the cats and mufflers count as part of the tailpipe length, since they're both straight-thru design. Using the info in one of the references,

http://www.ashraeregion7.org/tc26/pa...st_Control.pdf

the resonant frequencies for those tailpipe lengths calculate out to 2442 RPM and 2180 RPM, respectively.

The tube length should be a quarter wavelength of the resonant frequency so that it bounces back and becomes a half wavelength interference sound pulse. In my case, those lengths are about 2 ft 1 inch and 2 ft 4 inches.

Apparently sticking some fiberglass in the tubes will widen out the interference band and compensate for any real-world discrepancies.

I am sure there are plenty of fellow rennlisters that know a whole lot more about this kind of thing than I do, so please have at it.

If it actually works, what are the downsides? I can think of weight and placement for starters. On the other hand, it would be a pretty inexpensive change that doesn't add resistance to the exhaust stream.

 

My bimmer has a resonace muffler ( dead end) and an appendix pipe in the oem system. To reduce harmonics, I guess It works.

 

I had a quiet sounding S4 before, and it was running rich from intake leaks and other things. Everything will go rich (versus lean) when the car has issues. That is my guess for the op.

 

That's interesting, lspeed. Why silent when rich?

 

My 87 has an RMB and an X-Pipe with the high flow cats and it is a good blend of growl and quiet. There is a light drone on the highway but it is far from offensive to my mind and is more than made up for by the sound it makes when I jump on it.