I recently installed a muffler on my 98 D 5.2 and noticed its quite a bit smaller but has 2.5" inlet outlet and inside is the same 2.5" pipe. My question is would this cause back pressure? Also plan to exit in from of the rear passenger tire. Any thoughts or opinions would be great, thanks

 

it will only cause an increase in back pressure if the pipe diameter is smaller than the stock if it slips right onto the stock pipes you should be just fine

 

I do have one small peice of 2 1/4 as a fitting between the inlet and muffler but that shouldn't be a problem right?