I have a 2003 F250, 6.8L V10, 6 speed Standard. I am posting this in the F150 forum because maybe it works for those too, idk.

I wanted to put an aftermarket muffler on my truck to make it sound good and maybe gain some extra ponies and a little bit of gas mileage.

Now, Ive heard putting pipes on a V10 will make it sound like a 6 cylinder

So, I decided to experiment. The V10 has two, 2 3/4" pipes running off the headers into a Y 3" pipe. That connects to the Catalytic Converter which runs into the muffler and out the back of the truck. The muffler on the truck was attached by a bolt on strap. I undid the strap and worked the muffler off. I left the Catalytic Converter in place. Keep in mind, this is a factory set up.

I was about to put the Flowmaster on, when I thought, what the hell. I got in and started it up, just to see how it would sound. Too my surprise, it actually sounded good with no muffler!! Even after I revved it, the pipes didnt ping like I thought they would!!

IMO, it wounds like a Corvette exhaust system; A low, steady rumble when idling that drops off when you put it in gear. It has a lower sound than a Diesel truck, and we all know how noisy those are!

So I left the muffler off, removed it all, and kicked the tail pipe out the side, in front of my rear wheels. I think it sounds good, and have noticed an increase in power. I am hoping it will get me better gas mileage (im running a steady 15 mpg Hwy).
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thats great. are you worried that the lack of back pressure will hurt your engine??