I have a 04 f150 fx4 5.4 v8, ive been searching every where online that i can to find a stock exhaust diagram, to get the sizes and ive come up empty. Id go messure my exhaust, but its parked off base, and its raining out and i dont feel like walking over there, or laying on the wet cement lol. Im ording a muffler either the magnaflow 12588 si/do, or a flowmaster 44 series si/do. Thanks for the help.

 

Factory exhaust is 2 1/2''

 

2.5" with a 2.75 tailpipe is OEM.

 

Has it always been 2.5" or was that changed in 2004?

I seem to recall reading other posts about using 2.25" to avoid a loss of torque with true duals. Is that still correct?

Thanks,

KR-Texas

 

2.5 single oem,i recommend 2.25 in duals for tq retention

 

Still 2.5", only real difference is the mufflers got bigger & quieter, so did the cats, and the tailpipe was enlarged a quarter.

 

so we would need 2.5 in and 2.75 out to replace the factory muffler???

 

2.5 in and out-they can swedge outlet to 2.75

 

x2. Though if your going with a dual outlet muffler you will require new 2.5" tailpipes by your local shop so you wont need the factory tailpipe anyways.