Magnaflow 16741 problems

Cranch · March 16, 2012

Hey everyone just had the magnaflow cat back installed on my 08 silverado and while it sounds nice it's way louder then expected. It drones terribly at 2000 rpm and when coming to a stop it vibrates pretty bad. Any ideas? I looked under and the exhaust has barely any movement and it looks very tight to the heat shields when it comes over the first cross member. I'm starting to dislike it after only a week.

mdjordan2004 · March 16, 2012

I had a magnaflow exhaust built for my 2005 GMC sierra crew cab using two mufflers first one being part number 12867 (about $85,00 shipped to my door) and second one being 12219. I heard all of the stories of the cab drone and looked at another write ups on another site where someone used two mufflers. Here is a link to a site where I got some of my ideas. http://www.performancetrucks.net/forums/gm-engine-exhaust-performance-21/who-running-2-mufflers-series-460033/page3/

If you add another 14 or 18" long and 4 to 5" round muffler between the cat bolting plate and the existing muffler it will help with the drone and bring the sound level down to a nice low growl. I still have a little drone (or maybe it is just louder than stock is what I am hearing) but that is to be expected with any aftermarket system. Also if you do add another muffler go ahead and have the exhaust shop weld all the joints getting rid of the clamps. That might have something to do with the vibration.

My dad was and engineer with GM for 34 years and he said the harmonics most of the time come from the longest run of pipe before the muffler. There are also a few other things you can try but if the system is to loud for you as it is adding another muffler might take car of both problems. Don't worry about the exhaust flow, the mufflers are all straight through design just make sure you get a 3" inside dia. muffler.

Hope this helps.

Cranch · March 16, 2012

Ya that definitely is where the vibration is from. The pipe from the cat to the muffler. It seems so tight. Might be best to get something put on before the muffler. I think I may take it all apart this weekend and redo it. See if I can get a little movement out of it. I wanted louder but this is just ridiculous.

mdjordan2004 · March 16, 2012

You can also try clamping some lead to that long pipe with a large hose clamp. According to my dad use 2 pounds and try moving it starting from the middle of that pipe. What you are doing is changing the harmonics getting the drone to come in at a higher RPM outside of your normal cruising speed. If it is droning at 2000 rpm now maybe you can move it around till it hits at 2400-2500 rpm's. That is a place you would not be at normal cruising speed. If you want to make it tone down then add another muffler.

Good luck, I know it is crappy that you have spent this money on a new exhaust and it is not what you where expecting. I learned the hard way and had a local muffler shop replace my muffler (3 chambered Flo Pro) and crush bent tail pipe to a SS Corsa looking tip. It was to loud and droned like crazy, not to mention the MPG's I lost do to the crappy bending. My new exhaust was done using mandeal bending machine and I picked my MPG's back up. Having it dyno tuned next Friday to take full atvantage of the exhaust and my CSI. Hopping to pick up another 1-2 MPG's there and a little HP.

cparks555 · March 16, 2012

I want a nice sounding muffler also, but what you're going through is exactly why I haven't pulled the trigger yet. Hope you get it figured out, let us know what happens.

jdubub · March 16, 2012

I love my Magnaflow, mine is the 18". No drone, not too loud and the best sound IMO.

Cranch · March 16, 2012

Thanks for the info mdjordan. Appreciate it. I to have the 18 inch muffler but I have the entire cat back. Just seems like the system is so tight that there's no movement on it to stop the vibration. Gonna have to take it apart and see. It sounds good but just drones badly around 2000 rpm.