Last week I pulled my stock muffler off, and had a Magnaflow 12258 SI/DO installed, dumped with turn downs just before rear axle. When warm, I love the way it sounds. When cold, it sounds like the stock muffler, and is quiet until it warms up. Through searching, I have read that the muffler needs to be broken in. I have about 400 miles so far on it, with no change. Anyone elses Magnaflow quiet only when cold? How much of a break in will it need, and after its done breaking in, will it be louder at idle? Engine is the 4.7 liter if that matters. Thanks for any ideas or thoughts.

 

i believe you need tips for it to be loud at idle, i have dual 3" tips out the back and it sounds good at idle.

 

Its not just at idle though. While accelerating, cruising, etc when cold is quiet. When warm it has a nice deep rumble even at idle.

 

mine was on the truck when i got it so i don't know how long the break in period but i'd say give it some more miles.
you could give magnaflow a call and they should know.

 

Okay, you just answered my next question for you, which was how long did it take yours lol. I would have likely ended up calling Magnaflow anyway, just wanted more "real world" experiences. Overall though, how do you like yours?

 

i love it doesn't really drone at cursing speeds but has a nice da da da sound and at WOT it screams

 

I have to admit, I've never heard of having to "break in" in a muffler. That's a new one to me.

 

The sound on mine has not changed since installed a few months ago so if there is a break in period I didn't notice it. Did you have the resonator removed as well? I do some freeway driving so i love the fact that at 2200 rpm it is pretty quiet. Sound is very subjective to eack individual. You may need to go with a cherry bomb extreme to get the sound you want.

 

After looking at what kind of muffler you have, it is an 18" muffler which is a little quieter than lets say a 14" muffler. I have the Magnaflow 12198 (14") SI/DO dumped before the rear axle and it is a little quiet at startup but I haven't really noticed anything as far as it being quieter when cold. But it shouldn't be a problem... Just let the truck warm up a bit. I have also noticed my muffler is a little louder now than a year ago when I had it installed.

 

I noticed a change in the tone of my magnaflows after about 2-3 weeks running them. I also ditched the front resonator and put in a magnaflow Y pipe, and mine sounds nothing like stock at idle, WOT, or anywhere in between.

nateroach