Audi 4000 Turbo quattro Conversion
of rear half of 3" exhaust system.
For a turbo motor to work well it needs to breath well. The old rusting exhaust system on my car had to go. To start with it was 2.25 inch for the most part and had been spliced a number of times by different muffler shops. The catalytic converter also smelled pretty bad some times.
A word of caution: I did not read this elsewhere until I had already finished my exhaust system. Putting this exhaust system on a normally aspirated car will be VERY LOUD!!!
Since I first put this exhaust on before having the turbo motor installed I had to use a reducer adaptor to change from the stock 4k down pipe to the 3" exhaust. I used the same ball socket joint. For the non-down pipe side I cut part of the catalytic converter off and welded the adaptor to that. Right behind that I mounted the new 3" converter. Then a small degree bend and then a straight shot back to the middle muffler which I have slightly ahead of the stock location. Then the hard part begins. I put the 3" slip joint in the location of the factory ball socket. This lets you install the mess once it is all welded together.
I TIG welded everything. In no place was the smooth transitions of the mandrel bends not used. This was hard at the entrance of the rear muffler as I had to put the muffler all the way back to have enough room to make the 180° bend. The section of the pipe that goes from the middle to rear mufflers has 6 sections of bend, 3 straight sections, and a slip fit joint. That is were the bulk of my time went.
It took me the better part of two days to remove the old system and install the new one. I think in the future I could do it quicker. The lowest part of the car is now the middle muffler, but it is almost touching the drive shaft as it is. The rear muffler is too low, but that is just installer error as it could be moved up some.
I have not welded the middle muffler in place yet as I am still considering other options for this position. Once I am settled I will probably mark it, remove it, and weld it. Even without the turbo conversion I think the engine felt a little happier above 4000 rpm. Of course as loud as it was you did not want to run it that fast anyway.
3" Down pipe
To make the best of my efforts on the 3" exhaust system I continued all the way up to the turbo now that it is installed. Since the turbo outlet on the KH is just under 2 inches I had to use a transition cone (my terminology - I don't know what they are really called) to get up to 3". Since the stock exhaust had three tubes there was a good amount of space for the 3" pipe to come through. I added a 3" stainless steel flex coupler between the cat and the down pipe to keep things from cracking. The picture below shows the new down pipe next to a stock 5kt down pipe. Things are quite a bit larger now. In this picture the waste gate pipe and O2 bungs are not yet installed. I am using two O2 locations, one for the CIS sensor and one if I want to run my wide band sensor currently residing in the Race Rabbit.
Here is a picture of the down pipe installed in the car. Now the entire exhaust system is 3" mandrel bent from 1 inch after the turbo exit to the tip of the tail pipe. I still have some muffler clamps under the car as I want to hear the exhaust note before I make my center muffler choice permanent. At least now if the car does not perform well I can't blame it on the exhaust. Note also the thermal coating on the exhaust manifold and the heat shielding.
I think this setup is a little two resonant when the windows are up. It is very nice with the widows down except sometimes when it first starts idling. With the windows up it is starting to get a little old. I suspect part of it may be some section of the piping resting on the chassis. I need to get under there and rework the bends right after the cat. Once I put the down pipe in things did not match up perfectly. It is also possible that the resonance is due to the tail pipe ending about 1" before it gets out from under the bumper cover. I may just go get a 3" coupling and slip it on there for a test drive to see if that helps things. If it does I will rework the tail pipe.
On the plus side the exhaust note is VERY nice. It sounds very similar to my 5.7 liter Suburban V8 when they both idle. It gets louder with engine speed, but nothing that will attract too much attention. I noticed the other day at a light on a 3 lane road that when I pulled away I was the quietest car while accelerating. All the pickup trucks and such things around me were louder. My only contribution was that faint turbo spool.
I finally got around to recording the exhaust at idle. I have
it as a small video file in my Audi