I have Rineheart extreme tru duals with 3" Rineheart mufflers. I recently bought the RH 4.5", but they are the same diameter as the header pipe.
Have any of you ran into this situation? What did you do? Did you use an exhaust flange?

 

if you bought the mufflers new from an authorized dealer call Rinehart and let them know about the issue, they will help you get the coprrect fitting muffler for your head pipes. there are different sizes for different systems. Some of the slip ons made for stock head pipes wont fit the true dual pipes, make the call and they will help you get it right.
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Is the muffler split on the end? If so the end of the muffler may already be collapsed down and may need to be opened up. This happens all the time on new mufflers.

 

I did call Rinehart, and he said the 4.5 will not fit true duals. If i want to keep my header pipes I need to go with 4" mufflers or if I want to keep the 4.5" I need to change my headers to the slims.

 

Well there we go, straight from RH themselves.

 

Update
I got the Rinehart slims. They sound bad ***!