The stock Miata muffler looks possible. Obviously not plug and play but if the dimensions fit that center inlet could be used with the 2-1 downpipe going below the cross member like mine. Mods would be needed to incoperate the hangers designed to take the rubber mounts and not our noisy springs. Or you could flip it over, and have the 2-1 go above the cross member and contain almost zero bends before the muffler. There's so many aftermarket options for the Miata that surely one would fit our design quite nicely if the space is anywhere close to the same as the X1/9. One could always weld extensions to the outlets if the X1/9 is slightly wider, not likely able to shorten if its too big.
Yeah.....the stock Miata muffler looked to have potential. A while back I even bought one to see if it would work.
In theory.....it should be a good choice.....the center inlet should line up near a spot where a simple 2-1 downpipe would go under the crossmember and almost directly into it. That should be easy with just a couple of bends. My plan was to have the two tailpipes exit through the rear grill - my desired look. That would involve some cutting/rotating of the tailpipes. And of course fabricating some hangers.
In theory.....it should be a good choice......inlet size is about right - not too big......and surely should have easily enough flow - I think Miatas of that vintage (2006-2015 ish) were 2 litres with maybe 140 hp. And you would certainly think the Mazda engineers made it as less restrictive as possible to maximize performance.
In theory....it should be a good choice...the stock OE Miata muffler is a really nice quality piece - I think it is stainless - and comes with nice polished stainless tips that could surely be re-used. And you can get them pretty cheap barely used from someone who has upgraded to a performance muffler. I got mine for like $50 and it looks like new.
But.....in reality....i'm not sure. Fitting it appears to be a bit of a challenge. In person it is much larger than it appears in photos. And there is not a lot of room back there in an X1/9. As I recall, it pretty much fills all the available space. And as it is, the spacing between the tailpipes is slightly too wide to fit. They would have to be cut and tucked in closer to the muffler. And i have no idea what the sound or performance will be like. On the Miata, there is also a resonator further ahead in the system.
Yes, there are lots of performance mufflers out there for a Miata. And some would even appear to have a smaller muffler body that the stock one. So may be easier to fit. But most are quite expensive, and spending several hundred $ for one and then hacking it apart would seem to be kinda silly.....
So.....the jury is still out. I know others here like myself have bought one to try. Cant recall anyone who got further than I did........