Miata Engine Accessories Interchange
Published: April 11, 2018
NA and NB alternators have the same mounts and appear to be visually identical. However, on NA the voltage regulator is in the alternator; on NB the voltage regulator is in the ECU. Using an NB alternator on an NA will result in the car not having any voltage regulator which is a Bad Thing.
I don't know if an NA alternator will function ok on an NB.
Alternator pulleys and belts are also different between NA and NB - NA has a single rib belt and NB uses a multi rib design.
NA and NB have one of the three the starter holes in slightly different locations. The starter attaches only to the transmission, not to the engine; using an NB transmission and an NB engine/transmission gasket plate in NA chassis will allow an NB starter to bolt up at all three factory points.
NB engine/transmission gasket is slotted where the starter hole is to accommodate both NA and NB starters.
Lower Radiator Hose
NA uses a 3 piece hose: the center piece is metal and is fastened to the body, plus there are two short rubber hoses on either side. NB uses a single piece rubber hose from the engine to the radiator and has a plastic retainer that the hose fits into in the middle.
The shapes of NA and NB hoses are virtually the same. Retaining mechanisms are different, but can be made to work either way with zip ties.
Upper Radiator Hose
NA and NB upper radiator hoses are of different lengths due to the radiator inlet being positioned differently: on NA radiator the inlet is all the way at the end of the radiator, whereas on NB radiator the inlet is a few inches toward the middle. As a result the NA upper hose is longer than the NB hose. The angle at the water outlet is also slightly different between NA and NB hoses.
NA hose will mostly work on NB, though it will be bent more than it is designed for. NB hose will be too short for NA radiator.