Ok I tried to search, but it excludes the number 3. So here is my question.
I just bought an 01 f150 with a 5.4. Now from everything I learned from my mustang w/4.6 is that anything over 2.5 on the exhaust is to much. So on the 5.4 wouldn't a 3 in exhaust be to much? I want to do the cat back first, and later on will do headers, and maybe high flow cat's.

 

if you are talking true duals on a 5.4- 2.5 is ok use an x pipe- put it as close as possible to the the original y location-in my case with my van as being as heavy as it is & the fact i drive it and use the part throttle tq increases i got with my custom tuned programmer- i'm going true dual with 2.25 pipe- x pipe and magnaflow 4x9x14 mufflers-it'll still be better than the original oem 3" single- it's just the fact i want better torque between 2000-3500 rpms -thats more important than more hp between 4000-5400 rpms-now if i had an f 150 i'd go the 2.5 route for wore top end power- mustangs use 2.25 and it's good enough for 300 hp -3" single is fine for 1 pipe-duals with 3" would kill your bottom end- these heavy *** fords need all the power they can get off the line- hope this helps-phil

 

I have 3 inch duals on a 5.4 My highest torque is generated at about 2600 rpm and remains within 5 pounds of maximum all the way to 4200 rpm where it begins to drop off. I also have the flowmaster 40 series on there, which have been claimed to loose torque. I didn't notice anything like a loss.

 

more than likely he's naturally aspirated-turbos, superchargers and diesels benefit from less back pressure-my 89 ta with the grand national motor-i upgraded to 3.5" downpipe and 4" exhaust- now if i put true dual 3" on my van and dynoed it against true 2.25 or 2.5- i'm sure the hp numbers up top woul be better but the tq numbers would be less-my .02$ phil

 

Thanks for all the help. I'm just wanting to go with a siso set up for right now. Once I get my truck smoged in CA and get my base sticker I'll look into doing more of an x-pipe set up. I know on my mustang I put on a bassani off road x and with stock mufflers it sounded good. I know I'm not gonna get the same sound out of my 5.4, but I want it to sound different than stock.