Mufflers

OSCAR, I am having the same problem with my bxs, just put 7in pickets on. I'm going to try just a Donaldson resonator first. If that doesn't work I guess I'll have to put a free flow muffler on. What did you finally decide on and are you happy with it?

 

Hey Oscar I installed the Donaldson resonator this past weekend on my 379, I would say it is now 40% quieter and got rid of the drone sound I had around the 1400-1450rpm range.

 

Not trying to insult your intelligence, but could the "drone" be something other than an exhaust noise? i.e. trans or rear end whine?

 

I'm no expert by any means and hopefully Master Haney or someone with a lot more credibility than me will jump in here. But here is my un-educated explanation, when you change the timing in an engine it "moves" where the cylinder fires during the stroke which will slightly change the harmonics of the entire cycle of the engine. That's why you can "hear" the difference after the BD installation, or after the Haney tune. The down side to this is now that the engine is running at peak performance/efficiency so are the harmonics. There is actually 2 problems here 1st is mounting exhaust to cab, the 2nd is they changed isolator material. The problem Oscar has is a KW problem not Walker or Donaldson or BD or Cat. The problem is the hard plastic/nylon isolator they replaced the nice rubber ones with,(not bushings, they stopped making exhaust bushings about the same time they quit using muffler bearings lol). Even IF he could find a set of the good old rubber isolators he will still hear some of the drone,(because of the new tune) just not near as much. Before everyone starts yelling at me about Petes and Freightliners mounting exhaust to the cab, look closely at the isolator on the next one you see, probably good ole' rubber with a steel sleeve. Next time you see a long low 379 with 8" pipes and Pickett elbows, ask the owner how he liked the "new style last forever" nylon isolators that came with his kit. Then ask him how quick he went back to Peterbilt for the good ole' rubber ones. Now back to Oscar, first make sure ALL motor, trans and cab mount bushings/isolators are in good shape, part of your drone could be coming from some metal to metal contact at one of these points. Assuming your all good there, now we have to isolate the exhaust from the cab. You have already eliminated the weed-burner route, so that leaves only 2 options 1) go to a junk yard and buy all the brackets for a "vocational" T800, kind of pricey and about 200 lbs. with pipes and your going to lose 12"-18" of deck space between back of cab and front of trailer. 2) take one of the good ole' rubber isolator (if you still have 1)and/or 1 of the crappy nylon isolators and the stainless pin its going to slide on to a quality spring and alignment shop and I'm pretty sure they can come up with something close enough to work. I chose the weed-burner route because the (KW exclusive) 1 piece upside down ? elbows were beginning to "bubble up" under the chrome and we all know what is coming next with that. Besides they are $1400.00 each (American USD).
BEFORE...
View attachment 54611
AFTER...
View attachment 54612 View attachment 54613
Those are 3', I'm going to switch to either 4' (puts tip right behind steps) probably going to get a couple of 5' pieces and cut them down, but then I'm going to have to support the pipes if they are that long. I might try turning them down a little more, they are chalking up the steps and the front of my fenders.
http://www.truckpaper.com/listingsdetail/detail.aspx?OHID=4584233
Look at 4th pic to get some kind of idea about "vocational" brackets(KW's choice of words not mine) nothing touches the cab. By the way I have a complete used (needs paint) set of these brackets with braces that will be for sale, if I can make the weed burners work.