I have a 05 F-150XL 4.6L single cab 8' box, and i want to put a exhaust on SI/DO perferably. the only problem is i dont know what to get i want something that has a deep sound and doesnt have a drone. I also dont want to lose low end torque which the 4.6 already doesnt have alot of, but at the same time keep the same MPG's. YOur thoughts are greatly appreciated.

 

You aren't going to loose low end torque or gas mileage with a change to a catback exhaust unless your right foot get's heavier.

As to which, I can tell you the Flowmaster 40 SI/DO cat back does have drone with the 5.4 ( was on my truck when I purchased it, I knew something else was needed as soon as test drove it) and my guess is it would with the 4.6 as well.
To kill the drone, I added a 28" long 2.5" ID glasspack ahead of it. The perforated core of the glasspack gets certain sound waves and the chambered FM get's the rest pretty well. It worked for me.

Magnaflow is a good system, and there is Gibson and Borla.

 

roush, magnaflow,borla and many others, do a search im sure youll find your answer in one of the 100 threads about this

 

My 97 4.6 has a flowmaster setup and sounds nice. Seems to have plenty of low end for this motor

 

Borla Pro XS SI/DO. It is a 19" case muffler that will not drone in the cab very much at all.