I've got a 99 5.4 and true duals and i have noticed a torque loss and was wanting to regain some of that torque. i want a nice deep tone that has a little rumble to it. Any advice i'm thinking Flowmaster Super 40 DI/DO, but i'm not sure i could go with a Magnaflow. If i do teh flowmaster is DI/DO going to regain torque or do i need to go SI/DO??

 

What size pipe did you use on your true duals?

 

Pipe size is 2.5 in and out

 

With true duals, 2.5" is too big, you need smaller than that to keep your torque, plus a an H-pipe to even things out.

If you want to go muffler, I'd suggest headers to a Y-pipe, SI/DO muffler, dump it or run it to the back as you see fit.

 

Did you reset the PCM? Where are your o2 sensors and are you running MIL eliminators? What did you do with your cats?

With the bigger pipe, midrange torque will be boosted, enough sometimes for someone to think low end is gone since it will pull harder at higher RPMs.

 

the 02s and the cats are all still factory it's true duals back from the cats. if i decide to go with a muffle what do you guys suggest?

 

The Flowmaster 40 series, as widespread as it is, is a good muffler. If you want a good loud rumble, that's the way to go. For just a rumble, run the pipes after the muffler out the back of the truck. For a loud rumble, dump it right after the muffler.

I'd suggest a single-in dual out.

 

Dual in dual out Magnaflow should do the trick, you could get 2.25" tails put on after the mufflers. Go with an 18" body length.

 

Dual out on a Flowmaster 40 close after the muffler will definitely give the deep rumble:

Some other options are listed here:
http://motorhaven.autoanything.com/exhausts-mufflers/20A50460A1.aspx?kc=MOTORH

 

I can agree with ToughBuiltFord, I have a Flowmaster 40 that's dumped immediately post-muffler and it's very very deep and rumbly lol.

 

I have heard that simply adding a X-Pipe to a true dual system will really help with low end power and torque, I heard this from a guy on the forum. He has straights with stock cats, true duals, and a x pipe. He said he once had true duals with no linkage inbetween, and when he added the x pipe it was a huge difference, really helped the scavenging of the exhaust. I personally have a 4.6L with high flow cats, 2.5" true dual straights(no linkage whatsoever), angled out the back with 5X22" SS tips, I did notice a big drop in low end, but gained a lot at around 2000 and up. Just a lil info I thought might be somewhat useful.

 

The main reason you noticed the loss was because you went with 2.5" pipes, if you add an X then yes it will help. But you wouldn't have noticed it as much if at all if you had gone with 2.25", tune the exhaust and it makes a big difference as well.