new noob!!!
 

hi everyone,
this is my first post. i'm david in colorado. Im a international student, and got chance to turbo my miata!!! it is a 1990 miata na6. i want to make it to have 250whp from 1.6 engine. with a gt2560r turbo and fm2 exhaust manifold. some ebay exhaust. i already rebuild my engine with forged piston and rod and cam. i got 3000 left to spend on differential, body kit, brake, and other stuff. im stuck how to choose a differential. i heared some swap to a 1.8 differential. but i dont know if the original differential case will fit, what ratio should i do (use for track and fun) and what else should i change.
ps. my english is suck,plz dont challenge me on english,LOL.

new noob!!!
 

A 1.8 differential will bolt in, but you will need the axles also. They are a different size.

Welcome, davidlin121!

how about drivenshaft, do i need change it too? and if i change the axles, do i need new hub

Yes, you will need a new driveshaft form a 1.8 car. The hubs do not need to be changed.