[The Deuce]

Poo on Flowmasters. I say get a blower, 3.73's, and some Dynomax Ultraflows.

The main problem with the 4.6 motor is that it is starved for air. That's why the 03 cobra makes so much power. The eaton supercharger (a blower) forces the air into the motor, and solves what is essentially a design flaw.

I just like the way the dynomax's sound better than the flowmasters, and the 3.73's will give you enough highway gear and get up around town to be more fun than stock.

It all depends on the risk you want to take. You can get away with new mufflers, a K&N and maybe even gears without voiding the warranty. Much more than that and you are SOL.