I have this catback:
http://www.xs-power.com/mazda-exhaust-catbacks-1.htm

It does not look like it includes a presilencer/cat replacement pipe from the dealer... Though I got it used and mine came with a presilencer approximately the same size as the stock main (3rd) catalytic converter.

I also have the Racing Beat 1984-1991 6 port header:
http://racingbeat.com/resultset.asp?PartNumber=16130
(Website and brochure say different. The brochure that came with the thing said fits 1984-1991 13B, 6 port.)

Problem is, both are on the car and both the stock cat and the silencer are too short by about three to four inches.



I have not measured the stock cat or the presilencer that I have. In hindsight, I probably should have... But what can I put there that will make this exhaust sound decent.

The mufflers are straight through. They will most likely be LOUD. The header is obviously going to increase noise. Ditto with the presilencer...

I was thinking of going to a local exhaust shop (Meineke, Midas, etc.) and having them weld up either a custom length cat or muffler to go in this spot. I live in a residential area and need this thing to sound reasonable... (But I also need it to have a little kick. I need a little boost in power.)

 

Well the presilencer will help to make the exhaust quieter. I say take it to a shop and have them extend the pipe to whatever you need to make it fit.