I'm on about my 6th or 7th incarnation of exhaust setups on my truck since I got it in December...
started with stacks... loved 'em, but they got a little rowdy on the highway...
so I figured straight 5" exhaust would be quieter since it wasn't exiting right next to my ears... THINK AGAIN!!! the resonance was ear splitting... much worse than the stacks!
I got the setup from City Muffler. I've got a 4" downpipe going into a length of 4" ID flex tubing (from the stacks) into a 4-5" adapter located about 12" from the cab, and 5" after that.
to kill the resonance, I put the muffler provided w/ the City Muffler kit... obviously the resonance was greatly reduced, but the truck sounded neutered!!!
so I laid down a sheet of lead on the entire floor, the first ~14" of the firewall, and the back wall of the cab... with a double layer under the seat and on the back wall. I believe it's 1/8" lead sheet.
that quieted things down a LOT, so I straight piped it again... livable, but still got a little annoying on the ears in the 75-80mph range. so I put a 12" long Dynomax Bullet muffler about 2" from the turbo outlet. it sounded pretty darn good, and the resonance was totally livable at 75... got a little loud at 80 (2500rpm is this trucks peak resonance point) so I put the muffler on... WAY too quiet... but, I could drive at 80mph with NO problem... but WAY too quiet...
so I took the muffler off and just ran the bullet. I was content... the truck sounded good, and it was comfortable enough on long trips inside the cab...
last week, I added a couple more hangers and welded three band clap connections on the 5" pipe section because I decided I was just gonna leave it like that, and my tailpipe was sagging a little as the clamps had been off and on so many times that they'd loosened up a little.
well... a couple days ago, I decided "screw it, I'm putting stacks back on!!"
(I'm hopeless, I know...)
I figured that if the resonance w/ the stacks was LESS than with the straight pipe, the added lead sheeting just might make it livable on the highway...
so today I called the truck supply house and told them to get me a couple elbows and some straight pipe that I needed to do the stacks... I still have a bunch of stuff left over from before.
and I re-straight piped the downpipe to get rid of the bullet... installed the two pre-formed clamps on the flex pipe section and took it for a drive... sounds KILLER!!! (god I missed that straight piped sound!!!
)
hmm... doesn't seem to resonate as bad... roll up the windows and take it out on the highway... 75-80 sounds pretty much the same inside as it did with the bullet muffler!
ok, I guess I'll just leave it like this then!
if your aftermarket exhaust setup is resonating on you, lay down some sound deadener, weld up your pipe connections instead of using clamps, and you might consider a length of flex pipe in there somewhere.
I'm going to experament with adding some mass to the 5" pipe under the truck to try to cancel even more resonance, but as of now I'm happy as a clam!!!
Forrest
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