FZ1 exup motor and cables

[Fazafou]

If you remove the cat from the downpipes would this not have more effect on back pressure than removing the exup?
The exup is open or partially open in most of the rev range but the cat is like a honeycomb that has quite small holes in.

Removing back pressure is a good thing, it's exhaust velocity you don't want to lose, which the exup can help with.

The idea of 'back pressure' is a bit of a misconception http://www.gomog.com/allmorgan/exhaustbackpressure.html

Getting rid of the cat will help, going to a huge wide pipe can be detrimental though if velocity is compromised, so the exup can add a restriction to increase the velocity again. This all needs to be tuned though.

As long as the aftermarket pipes aren't too wide they should be ok, but I've noticed in the past on some bikes I've taken the baffle out of, the sound improves but power is down.