I'm in the process of determining the Magnaflow muffler to buy for my 2001 F150 Supercrew Lariat 4x4 w/5.4L. I have called Magnaflow twice and was given two different part numbers. I realize that it doesn't fit exactly as the stock muffler, but I am trying to get the one closest in size as I'm using the stock stainless pipes. The first # was 12286 which is center 2.5 in. inlet/2.5in. offset outlet. The second # is 12289 which is center 3.0 in. inlet/3.0 in. offset outlet. Doesn't this truck have 2.5 inch pipes from the factory? Also, the factory muffler has offsets front and rear it appears to me. Any advice is appreciated.
Lance in Brenham, Tx.

 

The f150s have 2.5-inch exhaust. If you are going with just the muffler and using the stock pipes I would opt for one of the shorter Magnaflow mufflers. I don't think there will be any difference in 6-inches of pipe being added or 12. I would make sure that were ever you take it or if you do it yourself to use stainless steel for the short piece of make up pipe. Being the stock muffler is a large round style the magnaflow being oval you shouldn't need it offset but on the outlet.

 

Stock pipe is 2.5" diameter. If you are only looking for a little more sound, a smaller chamber than stock Magnaflow is good with 2.5" diameter in/out.

On my two F-150's, a center inlet and center outlet would line up better. In or out does not matter as the muffler is not directional - straight through.

BTW, if you prefer the OEM stainless pipe, why are you choosing an aluminized muffler? Spend $20 more for the stainless (14xxx PN).