[TartanJack]

That is one of the most significant mods I have made and would say it was WELL worth the cost. That is still with stock header and exhaust. With an exhaust, it is supposed to be even better.

My only higher rated mechanical change is the sways. That would be a "must" for every xB. I don't know why the rear sway is an add-on and not stock. It should be. I have the Hotchkis sways and LOVE them! I am running stock springs and steelies with them too and the improvement is HUGE.

 

[TartanJack]

As all that is based on calculations from the odometer, speedometer, fuel level and fuel injector sensors . . .
And the computer automatically adjusts the injectors and timing based on other engine sensors (like the O2-> yes, it is crucial for the fuel/air mixture and not just for emissions inspections) . . .
Those should take care of themselves.