have stock 09 fxstsse3 110 engine and stock exhaust. Has anyone opened up the stock slip on mufflers for more rumble leaving converters inside mufflers intact?Is this possible or are new slip ons the way to go??

 

Unless the bike is a Cali bike, there is not cat; if a Cali bike the cat is in the head pipe, not the muffler.

If a Cali bike with cat, replace it with the '09 head pipes sold in the other 49 states; Ebay for about $200. Or the Fuel Moto head pipe, also catless.