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Mazdaspeed Miata Downpipe - Aftermarket with Catalyst


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For Sale: Aftermarket downpipe for Mazdaspeed Miata.

This is a bit of a niche part, but I thought I'd list it here regardless in case there happens to be an interested party with one of these cars locally.

With the cat installed, this part is legal for Street Touring in addition to Street Prepared (no cat required). This part would not be legal for Street category.

This started out as a catless eBay downpipe that I ran for 5 years as-bought. Really helped spool and overall throttle response. I got sick of the smelly exhaust and later decided to add a cat that was professionally installed early last year.

Catalytic converter is a Magnaflow spun metal cat with 2.5" inlet/outlet and 4" body; model 54956 (linky). Fits perfect in the space with the stock mid-chassis bracing, as shown in photos. It has two O2 sensor bungs, one at the rear behind the cat for the OEM rear sensor, and another one near the middle at the top for a wideband. One plug will be included (two shown here, but I need to keep one for my other downpipe).

Inside diameter for the inlet and outlet are 2.25" versus 1.9" in / 2.24" out for the stock part. Overall weight of this one is 7.4 lbs with the cat vs 16.4 lbs stock.

No issues with fitment, leaks, or cracks. Various gaskets are included for install, some have been used.

This will only fit your car if it has an Mazdaspeed Miata midpipe or some other custom solution due to the different flange locations vs non-turbo NB Miatas. If you've somehow cobbled an MSM turbo and manifold onto your NB, this downpipe won't fit with your stock midpipe.

I'm only selling this because I moved to a full RoadsterSport setup.

Asking $125
Located in Peoria, AZ area for pickup















Edited by CMarkmann
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  • 3 weeks later...


Also adding old video for sound test. Not completely applicable to this part in its current configuration though. This was with the downpipe in catless setup, with stock midpipe and stock MSM muffler.

Also important to note, my car passed sound at AMP with this part in a number of different configurations:

  1. Catless downpipe, stock midpipe, stock MSM muffler
  2. Downpipe with cat, stock midpipe, stock MSM muffler
  3. Downpipe with cat, stock midpipe, Roadstersport RS3 muffler


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  • 3 months later...

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