Does your NB Miata have a stock exhaust? Do you want a little nicer sound without spending $400+ for an aftermarket muffler, or even more for a FULL PERFORMANCE EXHAUST, GUARANTEED +2 HP?
Find an OEM Mazdaspeed Miata muffler and bolt it right on. From the cabin while driving, you don’t hear a whole lot of difference: low and midrange has a little lower tone, high RPM is decently louder. While I haven’t driven it on the street without the hardtop yet, I really can’t notice much difference while driving the car, even with the windows down.
HOWEVER today was race day. Here are some comparison videos, both using the exact same audio setup and placement:
OEM non-Mazdaspeed muffler:
And now the OEM Mazdaspeed Miata muffler on a naturally aspirated 2002 Miata:
So, to recap: Mazdaspeed Miata muffler gives an otherwise stock NB Miata some nice extra sound for cheap. I bought mine off a guy in the local Miata Facebook group for $25.