There are several manufacturers that make dual tip mufflers for the Miata. Turbocharged Miatas may benefit from a larger 2.5" or 3" exhaust.
Please see related links below for Miata-specific vendors.
Stock gap recommended is 0.040", for Turbocharged or Supercharged Miatas 0.034" is recommended.
There is a great website that has many listings for used 1990 Mazda Miatas. The website is Lemonfree.com and they have several listings for the 1990 Miatas.
Mazda Miatas do not have struts (they use shocks), so the braces that go across the engine bay are not absolutely necessary or beneficial as they would be with vehicles that have a strut setup. Shock tower bars on Miatas do tend to add rigidity, but there is a very mixed consensus by Miata enthusiasts on whether they offer a lot of value on Miatas.
No they are not. Their convertible tops tend to wear out fast.
Volt waggons, Miatas. and most sports cars.
The fuel filter for all 1990-2005 Mazda Miatas (including Mazdaspeed Miatas), is underneath the car, just before the rear tire on the left side. It will be hidden under a thin, plastic splash shield.
NB Miatas have the IAT sensor located on the black, plastic airbox towards the top on the driver's side. The sensor is simply plugged in with a circular, rubber grommet. NA Miatas have the IAT sensor located inside the Mass Air Flow sensor.
No, they have standard dual overhead cam, piston engines, at least from 90-05.
No. Mazda Miatas run a non-interference engine.
Miatas don't have struts. They use coil sprngs over shock absorbers at all four corners.
2001-2005 Mazda Miatas required a minimum of 91 octane.
1999-2005 Mazda Miatas do not really run MAP sensors like Hondas, they use a Mass Air Flow Sensor, the black, tubular piece on top of the air box. Miatas do have a boost sensor, and that is located on the intake manifold, half way down on on the lower section.