i have a 94 f150 with the 5.0 and im gonna get a Y pipe with no cats into a SI/DO flowmaster super 40 and 45ed out the back into 4x18inch tips. my question is pipe size? i know a guy that has 3 inch pipe all the way back to the muffler. would that cause me to loose torque? ive thought about 2.5 through out

 

No, the y pipes will also cause back pressure, so will the mufflers, and what muffler outlet size pipe are you using? You would probably match that, unless its 3" in and dual out muffler.

 

im not sure what size piping im using. if 3 inch piping from the manifolds to the muffler will cause me to loose low end torque then im gonna do 2.5 from the manifold to the tips. but the set up im asking about is 3 inch from manifold to muffler, then 2.5 from muffler to tips

 

No you will likely gain some by opening the exhaust, dont forget you are using stock manifolds and y so there is your back pressure.

 

I'd say 2.5 off manifolds merged into a 3 inch then running into the muffler and 2.5 out the back.