My Gasket Recommendations for aftermarket exhausts by mx5mia

3 minute read

My Gasket Recommendations for aftermarket exhausts

Compliments of mx5mia @ www.miata.net

Thru my own trial and error, I have come up with some suggestions that I have found to work perfectly on NC aftermarket flange mounting exhaust systems.

I found the hard way that if there is not a perfect seal between the mid-pipe flange and the muffler flange, an annoying booming base comes up thru the trunk and into the passenger compartment. Below are pictures and my recommendations based on what has worked well for me.

** "IF" you have the FACTORY Mid-Pipe and a flange mounting muffler (like the RS II and RS "Q"). Use a new Mazda O-Ring gasket # LF45-40-305. This O-Ring will stay in place while bolting the muffler in place. Plus it will seal perfectly around the pipe and on the face of the flange. See the 3rd, right picture below.

** If you already had an aftermarket muffler on your Miata with the factory mid-pipe, there is a 99% chance your Muffler AND Mid-Pipe flange ears are bent from tightening. If you now want to install the flange mounting Aftermarket Mid-Pipe (like the RS Mid-Pipe), I recommend you do not use the thin flat metal gasket that comes with the Mid-Pipe. Use the Advance Auto # 31512 gasket as it has a double thickness around the middle. This will seal even if the flange ears are bent a little. See the 1st, left picture below.

** If you are buying the muffler and midpipe to install together new, you may get away with the supplied thin flat metal gasket in the middle picture below. But if there is any waviness to either of the flanges it will not seal.

My bottom line recommendation based on my trials and mistrials is this:

* Use the Factory Mazda O-Ring muffler gasket as long as you are using the Factory Mid Pipe, and the muffler has a flat flange.

* If you are using an aftermarket Muffler and Mid-Pipe that BOTH have flat flange mounts, use the Advance Auto 31512 gasket. (As on my Miata now)

I hope this has been of some help and will save you the trouble I have had.