|0 inches = downpipe exit
The system starts with a manifold (not seen here) and downpipe from a 4000 Quattro.
The orange thing is a cap for the CO test tube outlet.
|0 - 17 inches|
Normally the 4kq catalyst follows, but the coupe floor pan does not leave room for one here. So the next piece is a curved pipe, like the one I cut and welded here from spare parts. This piece should point straight to the rear of the car and be nicely centered - this one isn't, really. This pipe is also where the OXS bung is mounted, unless your cat has provision for one.
|17 - 41 inches|
If desired or required the catalyst is mounted next, under the stock Coupe heat shield. This particular unit was removed from a 1980 5000 Turbo. I do not think a 4kq unit will fit here, since it is a wide flat design.
|17 - 61 inches|
The section after the catalyst should run straight down the center of the tunnel.
There was a conflict between where the curved pipe I made enters the tunnel (a bit to the port) and where the rear pipe lines up (too far to the starboard). This resulted in small but annoying (noisy) leaks at the cat joints. So I chopped out the cat (pasted back in here for show) and clamped in a piece of pipe. This smoothed out the racket to a growl that only bothered people behind the car.
Then, unfortunately, N.H. changed their rules and pre-1985 vehicles that had catalysts were required to have them. (11/99)
Rear edge of floor pan.
|61 - 81 inches|
There are two hangers here, normally for the stock middle box, one just behind the rear edge of the floor pan and one just ahead of the panhard rod.
|81 - 92 inches|
This is one of the difficult parts - humping the pipe up over the panhard rod and the rear axle without anything hitting when the car is in motion. I think this is best arranged with the cars weight on the road wheels.
|92 - 127 inches|
Straighten out and set up for the rear box, which hangs from two brackets at the 110 inch mark. This muffler is also from the 1980 5000 turbo, and is a straight-through perforated pipe design. I would love to use a pair of stainless glass packs here - side by side, each with their own tip protruding from under the bumper.
The tail pipe and the coupe bumper. Not a pretty sight from this angle!
|I think the bumper was designed for the 4kq and used on the coupe to make my life miserable. The cutout is lined up nicely for the way the laterally mounted rear box on the 4kq sets up.
On the coupe, however, the longitudinal muffler is not aligned with this notch and the tailpipes have to jump sideways about a foot (if the rear box has a center outlet, anyway) to get to it. I hope to get my bumper fixed so it has no cutout, by plastic welding in a section of a donor bumper. Then the tailpipes can shoot flames straight out the rear.