04 ZX10 Exhaust Mod

G'Day all,
I have a 04 ZX10 that I have just fitted a new muffler to. I do not have a power comander, that is next on the list!!
My question is should the Butterfly valve be left in or taken out. I have been told that if you remove the valve in the exhaust it will not harm it but will improve the power and make it a bit louder.
Any advice/recommendations

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leave the butterfly in.
you wont need a power comander.

Thanks Wattie
Have been getting conflicting reports. You mentioned no Power comd, is that because im just putting on a can or is the fueling adjustable on the stock setup??

just the can wont hurt anything. once you remove the valve you need re-mapping to get the best out of it.