stock exaust size on a 2001 ford superduty

[jbuller]

Hello, i have a stock exuast system on my truck well it looks like a 4 inch system to me. is there a performance difference in the aftermarket 4in systems over the stock other than the muffler? it does look like 3 in right out of the turbo them imediatly turns into 4in pipe. thanks

 

[dboyw]

Pure stock should be 3.5 inch. With a four inch, it is four from turbo back, nicer bends for the down pipe, and a straight through muffler. Helps in lowering EGTs

 

[jbuller]

thanks

will the 4 in custom systems still be the 3in right out of the turbo then turn into the 4 inch?

 

[dboyw]

If I remember mine correctly, it will have a flange to fit the turbo, but it is four inch completely.

 

[jbuller]

ok

so this is the question, will it give me noticable power gains? and noticable mpg change? is 4in really that much more than 3 1/2" as far as a stock truck goes?

 

[dmd]

Inside the muffler the pipes are 3-inch. That is where most of the restriction is. If you
cut out the muffler and add (or not) a straight through 3-1/2 muffler you will get
85% of what a 4-inch exhaust will get you. If you have a modified truck, you will
want a 4-inch.
If you just want lower EGT and a little more power then just swap the muffler. BUT if
later you mod the truck, get the 4-inch now...

I did my mods over a weeks period, added NAPA filter with no noticeable change. Added
chip with huge change. Added 4-inch exhaust and was like getting the power of the
chip added again to what was already a huge gain.