I am thinking of changing out my muffler. I am looking for something to help keep my EGT's low. I am not looking for noise or high performance. All I have done is to plumb in a 4" air intake line that picks up from behind the bumper and attaches to a 4" flange I installed in the bottom of my airbox. I am probably going to put in an amsoil filter. From what I have read here the donaldson will reduce the backpressure and help keep things cool. (I tow a 5th wheel and gross out around 18,000 lbs.) The 51" muffler looks like a tight fit even on my 8' box. Which would one would be best considering I don't what too much more noise. (I still talk to my wife!)
thanks for your input.

 

The 51" has no drone when under load.

 

Like TurboTed said...the 51" has NO drone under load. It is a lil' bit of a tight fit under my short-bed quad cab truck but its fine. Only issue I had was the muffler shop messed up and mounted it against one of the rubber cab mounts...MAJOR VIBRATIONS! Quick fix though...all is good now.

I love mine!

 

I like my 40" Nelson...

 

No it shouldn't be a tight fit under an 8' box. Here are a couple pics

 

You should not have any problems with a LB. I just had mine installed on my SB. Fits fine and sounds great, not loud and no drone.

 

I had the 51" nelson on a short box 03 without a convertor, and it sounded great. It has no drone under load. I have the 40" on my 05 with the convertor, and I like it, but you do get a drone when you are towing in 3'd uphill, etc. The 51" will fit a shortbox with the cat, as several people on here have installed it.

 

I have a 40", have not had amy kinda drone yet, pics, part no. in my gallery.
51" is longer than the factory muffler, I didn't want it to be TOO Quiet!

 

The 51" Nelson has a really nice mellow tone.(Nicer than the stock.) Don't forget, it is a straight thru 4" muffler as compared to the stock-twisted-restricted one. There is nothing from one end to the other, and there are no bends. The reason my 40" nelson has a bit of what I call a drone when I really work it is that the diameter of the 40" is a few inches less, as well as the length. If you look through the length of the 40 or 51" they are both the same- a 4" pipe going straight through.

 

...and I haven't really towed with mine since the install, have packed some weight with it up the hills and I didn't notice anything I'd call a drone, we could carry on a conversation, listen to a CD or whatever.
I'm heading out on a 3 week trip in a week with the trailer, boat etc, I'll know more after that.

Good thing though is the Nelson/Donanldson mufflers ar so cheap it's not the end of the world if ya gotta try another one...

 

where dose a guy find a 40" donaldson

 

Not sure, but the Nelsons are available through Cummins, and from what I've read on here in the past, they are pretty much identical to each other as far as quality, performance etc.

 

Turbo Ted, my 51" is a 5", not a 4".

 

You can get them in different diameters. The model #'s have been posted on other threads on here, but I don't have them at my fingertips. They also have models which are not purely straight thru. They have a screen type thing midway. Some guys bought those, and punched out the screen, but why bother?Just get the right model #.

 

Here's a cross reference you might find handy
http://www.cumminsfiltration.com/pdf...s/LT32002D.pdf