4 -2-1 pipes
4 -1 pipes
They dont sap power so much but change the delivery.
One makes better top end and one more nidrange. Cant remember which is which but I will assume it's 4-2 -1 is midrange as I have that on my bike

Yeah, I'm pretty sure the 4-2-1 gives the mid. That's what I'm looking for really.

Still no definite answer to the NC29 NC23 interchangeability?

I've tried searching the forum. I think the method used to search is pretty poor tbh but maybe I'm being a douche n just haven't looked hard enough. Still... Would someone please spell it out for me.

There's a thread in the CBR workshop section about it.