Just acquired a 2009 R3 that has been on the east coast. Took a look under and noticed the exhaust pipe between the muffler and midpipe has some corrosion and does not appear to be stainless steel (was also surprised to see it is a slip on joint to the muffler.)

Is there is reason Mazda did not make this pipe out of stainless? All my Miata's have stainless exhaust piping.

Also, does anyone make a stainless replacement?

Finally, my clamp for the slip-on needs replacing. I don't have a large caliper. Does anyone know the diameter of the outer flange on the slip-on joint?

The exhaust pipe part # is N3R540600.

Part diagram: Exhaust pipe in parts fiche

 

I have a feeling it's 409 stainless. Surface rust yes, but not penetrating.
304 stainless is more expensive and the shape of that pipe might require a more ductile alloy.

Most catback kits include their version of that pipe.

 

It was a slip joint until the factory clamped it, which forces a sealing indentation around the full diameter. It’s not easy to get it apart after they do that. If it’s loose/leaking then someone likely tried to separate it and found that out. I seem to recall that it’s somewhere around 62mm OD.

 

Yes. Looks like some aftermarket manufacturer of cat backs using a different style for this exhaust pipe, often with a flange rather than a slip-on.