[Treeve]

Lets also not forget tune. tune a brand new motor with a wideband and I'm certain your emissions will be worse than tuning with a narrow band O2 sensor.

There's a reason manufacturers use narrow band sensors, and it's all about emissions, not about power.

I've got stacks of IM240 test results from lots of different motors, and it comes down to:
1. having it tuned for 14.7:1 running in all load scenarious - not lean, not rich, and not a powah tune.
2. having good quality cats sized to the motor, and
3. having a motor in good condition.

Treeve