Went to a local Meineke Muffler shop and had a Flowmaster 40 Series installed on my `99 F150 4x4 ext. cab with the 5.4. I did this as an April Fools joke on my wife, since it is her truck and she hates loud exhaust. Price was a little high, $142.00.
The Meineke guy said that it would be too loud and I should go with the 50 series. What a load of bull!
The truck is noticeably louder, but just barely. It has a nice mellow sound at idle, and has a nice throaty sound when accelerating. It is barely noticeable at 65 mph.
To me, it sounds like what the truck should've sounded like from the factory. With my K&N air filter and modified intake, the intake sound is now about the same noise level as the exhaust, a nice performance sound, but nothing really radical.
If you are wanting improved performance without a lot of noise, this muffler seems to do it.
I tested my mileage just before the muffler install and it got a pathetic 14.8 mpg. I will test the mileage again when I make my monthly drive up to Spokane and post the results.
Low end power seems to be improved and mid-range power is definately improved. I got into a little race with an `01 SuperCrew up an 8-mile long, 7% grade on the way home and I was going 85mph with plenty of power to spare, the SCrew couldn't keep up .
Well, my April Fools joke will be a bust, since the truck isn't much louder, but that might not be a bad thing.

 

ya these new fords are super quiet. i think it might have something to do with having 4 cats. when i put the gibson on my expy, i fired it up right after i pulled the stock tail pipe and muffler off. and the thing was the same loudness as my 94 Chevy(that has a muffler).

the 5.4 is a quiet motor, but it has a good tone to it i think.

 

Tested my mileage today and got a whopping 18.7 mpg, up from 14.8 last week. Of course, I was babying it and didn't drive my usual route, but hey, I never thought I'd see that kind of mileage from this thing, no matter how I drove it.

 

Wait a couple months on the moise level. The Flowmaster will get louder. I had mine (FM 40) last August, About December is when my wife noticed that it was louder than when I first had it installed.

I never realized how loud it was until my wife was driving it one day. She left the house and I could hear the exhaust from a block away!

 

It's going to get louder?


-Now you sound like some of the newbies on the mustang boards.