How come on a Z31 84-87s have a T3 and 88-89s have a T25 and the exahust manifolds are IDENTICAL??

***Even though the 84-87 Z31 had a T3 turbine housing the flange was still a T25. That is why it fits on the newere 88-89 manifold without modification.

Just like you can get an HKS GT3037 with a T25 or a T3 turbine inlet flange.