Ihave a 2004 ford f150 5.4. I was just given 2 borla mufflers that are basically brand new. They are 3.5". Right now I have 2.5" pipe from my headers through my cats, then it flares into 3" piping to my flowmaster, then that has dual exits that are 2.5" pipe. Would it be possible to split my exhaust in the 3" pipe range and flare it to the 3.5" for the borla mufflers then flare it back to a 2.5 or 3" pipe? Would I loose to much back pressure, torque, or power??? I also posted this in the 2004 to prestent thread but i had no luck so far. Sorry if you have read this twice.

 

That wouldnt be a very good setup. 3.5 is WAY too big for duals, plus you would be bottlenecking the exhaust at the end... You would more than likely lose quite a bit of torque with that setup.

 

You would experience a great loss there. 3.5" single exhaust would be too thick, 3.5" true duals would be much too big and you would feel a very noticeable power loss.

For true duals, no larger than 2.5",

Single, no larger than 3"