Custom exhaust tuning... help needed

[QSHIPQ at aol.com]

Common problem, turbo or N/A I5 Audis.  The mid muffler is what tunes out the 
resonance at highway speeds, however it also sucks midrange and highend 
power.  A couple of things you can do:
Put the cat back in, it also muffles sound.  High flow cats are best for 
this, I've found good luck using 3in cats on 2.5in systems (this brings the 
"urgent" tone down).  This also works in the center muffler application.  The 
best muffler for the center in terms of height and clearance is the 12in 
Borla XR1.  Again, going with the 3in version of this will create a lower 
tone, and really address the midrange drone, without sacrificing power.  As 
far as the rear muffler, I use the Borla (expensive) or the walker dynomax 
(best b4b) ultraflow.
As for what you have stock to work with, I haven't had a lot of luck using 
any "glasspack" type mufflers in the audi I5, they don't really do much in 
terms of quieting this unbalanced motor pulses.
As a rule, deleting the center muffler gives you great gains in midrange and 
high end flow, but *always* at the expense of the sound right where you drive 
the most often (a subchapter of Murphy's law applied to audis).  

HTH

Scott Justusson
QSHIPQ Performance Tuning
Chicago
'87 5ktqwRS2 10vt w/ 3in turbo back exh, 3in high flow cat, 3inxdual2.5 borla
'87 4Runner turbo w/3in turbo back exh, 3in high flow cat, hooker turbo 3in 
'84 Urq - formerly with 3in turbo back scorpion (dual muffler) w// 3in high 
flow cat
'83 Urq - stock rear and cat, flowmaster 2.5in center muffler
'85 FJ1387 - SS headers, supertrapp exhaust w 8 plates ;)

spokes at mail.the-wire.com writes:
Car: 1989 audi 90 quattro

Earlier this year I decided to do some custom tuning of the exhast system on 
my 
car. (look for a webpage coming up soon...i'll drop a URL to the list, photos 
will be taken on friday)

I replaced the stock rear muffler with a 12 inch resonator (2.5 inner dia). 
The 
result was a pretty darn sporty sound!  It's loud, but not super-rice-boy 
loud. 
It does, however, have a very annoying drone right at 3000rpm. 3000rpm is 
right 
where I end up sitting for normal driving.  

The result of the modification was a large increase in throttle response, the 
car now pulls all the way to the redline...it used to just die at 4500-
5000rpm...continually adding revs but not increasing the power much at all.

I'd like to 'tune' the sound, but without an exhaust lab that isn't the 
easiest 
thing to do! All I want to do is get rid of the drone at three thousand rpm. 
I 
don't mind going a little louder, I'd be happy just to 'move' the drone to a 
higher or lower rpm range too.

I haven't touched the centre muffler yet, it's an aftermarket stock 
replacement.

I have easy access to:
12", and 15" resonators
15" long universal mufflers round or oval shape
I can have anything custom made with an 8-14wk turn around (so, if I wanted a 
6" resonator...)



Any ideas as to what I should start playing with?  Now that my job requires 
lots of highway driving, I REALLY need to do something about that drone!

-Dave