on a 97 f150 5.0 w duel exhaust, no cats, and an H pipe right where the cats would be, I just installed two new 17" Dynomax Ultra Flow Welded mufflers, and when I ran the truck for the first two days, it sounded very metalic, high pitched and for sure not broken in. How long will it take for the muffler to be fully matured???Please, anyone?

 

I would say around 500 miles.
That is around how long my magnaflows took.