Looking for advice,

I have stock headers and SE touring mufflers,SEST  and Heavy breather air.

I plan to cut open exhaust and remove catalyst and flapper valve.I saw it somewhere else here  http://www.fullsac.com/headpipe-mod.html   and think it will produce a more free flowing exhaust thus better running motor [they say about 10hp improve.]

My concern is : what about lost back pressure ? Is this anything to worry about ? Will this result in less power? Will the valves be ok?

Hope you guys can help.

If I was you, keep the standard mufflers for a rainy day and buy yourself some slip ons or full exhaust system.