When you're dropping a 1.8 engine into a 1.6 Miata, you need to keep the 1.6 throttle body to work with your old ECU. Adapting this to the new manifold is the biggest part of the job.
This adaptor will allow the throttle body to bolt up to either a 1994-97 or a 1999-05 manifold. The throttle body does not need to be modified at all as the adaptor is thick enough to allow clearance of all parts. Two holes need to be drilled and tapped in your manifold then this adaptor bolts right up. Includes all necessary fasteners. Save yourself some trouble!
Included in our 1.8 conversion kit.
Note - this will move your throttle body forward about 11/16", or 17mm. The 1.8 engine is also longer than the 1.6. Your existing intake will need some modification.