JDM motors run clean. If you keep a Cat your fine.
I have never been in or tuned a 2.5 that was as smooth or as fun to drive as a V7 or V8 EJ207. That includes:
Crawford,
Axis
DPR
Cosworth
GuppeS
STI
The 2.5 is just not a smooth motor. Its not the balancing. Its the Bore to stroke ratio. Its so oversquare its "chuggy".
Clark