Bolt-on naturally-aspirated power is the worst value in the Miata hobby. Intake, header, and exhaust on a 1.6 or 1.8 net only a handful of horsepower for real money, and that's the honest truth every experienced owner will tell you.
The stock engines aren't badly restricted, so the classic intake/header/cat-back trio gives small, single-digit-to-low-double-digit gains, mostly up top. Do it for sound, throttle response, and weight, not for a dyno miracle.
- Intake: A good panel filter or intake helps breathing and induction noise, but expect very little peak power. Skip the ones that suck hot underhood air.
- Header: The single best N/A bolt-on, and even then the gains are modest. A quality 4-1 or 4-2-1 header wakes up the top end and sounds great.
- Exhaust: A cat-back is mostly sound and a little weight savings. It won't transform the car.
- Tune: On NA/NB, meaningful standalone tuning matters far more once you've added airflow or forced induction; on a stock N/A engine the ROI is small.
Things that are genuinely worth it N/A:
- Reduce weight (lighter wheels, delete dead weight) for a car that already lives on being light.
- Bigger cams and higher compression add real power but require a build and tune, that's engine money, not bolt-ons.
Here's the community consensus, stated plainly: if your goal is more power, don't chase N/A bolt-ons. Every dollar spent on intake/header/exhaust buys almost nothing compared to the same money toward a turbo or supercharger. Spend on handling, spend on tires, or save for boost. N/A bolt-ons are for the driver who wants a better-sounding, slightly sharper car, and that's a perfectly good reason, just go in with honest expectations.