I got a HUGE Magnaflow on my F-150 (5x11x22) and it's too quiet now. I am dropping down to a 5x8x18 after the new year. I have a 40 Series Delta Flow on my Z71 and want just a tad less sound than that via a Magnaflow...so I think that 5x8x18 will do that for me.

The one I am going to get is a dual 3" in/dual 3" out. I am going to Y it down to a single 3" to use with my current setup...will go true duals when I get that 408 figured out.

Remeber headers make your vehicle considerably louder.