Downpipe - 1 piece or 2?

[ihasmazda]

Is there any benefit of a single piece downpipe versus 2 piece?

I see that both CS options cost the same, whether you get the single piece catted downpipe, or get the catless and then add a catted test pipe.

It would seem to me that a 2 piece would make more sense as then you can remove or replace just the cat/test pipe if you wanted to. Might be easier to install with two pieces too.

[SpencerC]

First Cat is monitored, second is not, if you replace the second cat and not the first, you will throw a CEL.

Likewise the flex coupler in the middle of our single piece DP w/racepipe is going to allow the system to move with the body vs. engine so it places less stress on the system.

[motherfnmonsta]

one piece is less likely to have exhaust leaks compared to a 2 piece, from what I heard the one piece is harder to install compared to a 2 piece.

[ihasmazda]

Makes sense that the 1 piece is harder to install, especially on the MS6 from what I've read. I've got an AP so CELs aren't a concern.

As far as leaking, I've actually read many a forum where the flex connectors like to leak on different cars. I don't know if it's common on these motors though.
As long as the donuts are good and the bolts are tight, the 2 piece shouldn't have any leaks I would think. And if it does, at least it's something you can fix yourself, unlike the flex connectors.

I hear you about the flex taking stress off of the engine movement. In makes sense in theory, but does the stock exhaust have any flex fittings? I don't think it does but I'm not 100% sure... And before my new motor mounts, my engine moved quite a bit (PMM was blown), so I'm not sold that the flex fitting is really that needed if there isn't one there from the factory.

So for ease of installation, eliminating the possible flex fitting point of eventual leakage, and removable cat option, I'd probably lean towards the 2-piece unless there's something else that I'm missing, which is very possible...

[SpencerC]

It doesn't have any flex couplers, it uses something more like a ball and socket over gasket joints, with springed screws to allow flexing.