Mbrp Drone..........

[bkroupa]

Update:

I installed a "New" muffler that MBRP has developed.

I may have the quietest 12V exhaust in Texas

The drone is down to a level that I would not have really ever noticed if I had not been chasing it. My stock exhaust was simular to what I have now inside the cab, my stock exhaust minus cat & with a small walker muffler was louder in & out of the cab.

Dealing with MBRP's customer service was a very pleasant suprise.

They were very interested in helping to solve the problem & offered many suggestions to try to allieviate my drone. The LWB QC trucks seem to be the most prone to doing this because of the natural frequencies of the truck, Cummins & the length of the exhaust. My EGT's are actually lower with the new muffler design, but it is slightly cooler outside today. Anyone who is interested in a quieter version of MBRP's exhaust you'll have to request this muffler to get it & you may have to get them to ask Martin at MBRP about it since I have one of the first production models on my truck.

 

[Gary - K7GLD]

I have consistently felt - and pointed out - that the mechanical drone is a product of a physical vibration/resonance in the exhaust system that can be aggravated by a "floating" exhaust that doesn't physically restrain the system from vibrating at some engine RPM point. Then, the exhaust "vibrates", much like a guitar string, and causes a mechanical buzzzzz along with an audible sound. I cured the drone on my stock truck by addition of a heavy length of 2 1/2 angle-iron up ahead of the muffler - and adding a couple of exhaust hanger restraing straps to also restrain the vibration.



#ad




#ad




All that effort worked great - but is not the sort of activity a fella wants on a nearly $1000 system...



Why do some trucks do it and others not? Possibly the state of tune of the engine - a little more injection advance *might* create a sharper combustion event, aggravating and increasing the tendency for engine and exhaust system vibration.



Just a thought...

 

[Forrest Nearing]

also, I think some people are just more sensitive than others...



I welded angle and strap to my downpipe and the long section of 5" from the bed to the tailpipe. I also welded about a 5lb sch 40 3" elbow on top of the front part of that long section of 5". I have VERY stiff exhaust hangers... but I also have a length of flex pipe between the downpipe and the rest of the exhaust.



a buddy of mine ran really stiff hangers on his 5" system, but no flex... it cracked the downpipe and the exhaust manifold! (and still resonated like crazy)



Forrest

 

[Gary - K7GLD]

The goal of my efforts above were to change the mechanical resonant frequency of my exhaust system with the weight of the angle iron, and also dampen it with the extra straps - fortunately, it worked for me. But in a more stiffly mounted system, the length of flex pipe up at the engine is a good idea.

 

[Forrest Nearing]

my goal was the same as yours



add mass to the pipe itself and use the mass of the frame to help dampen it furthur.



as you said, it's all about vibration... that's all sound is...