MC8 Muffler

[bevans6]

Resonators are designed to be used behind another muffling device, in my case a turbo.  Mine isn't significantly louder than the stock muffler without a turbo, and the actual engine is a lot louder than the exhaust at idle.  Donaldson makes the exact same device as a muffler, 10 - 15 dB quieter, and that would be perfect for a non-turbo engine.

[Jim Eh.]

If we have resonators we would still be much quieter than a Harley with straight pipes with the radio turned up loud so that everyone can hear it over the pipes. 

True, but a Harley doesn't stay within earshot nor on the throttle quite as long as a 35,000 lb bus going up a slight grade from a controlled intersection.

[Glennman]

1974 MCI MC-8, 8V71 turbo. Ok, so I decided to do some experimenting. The thought of possibly increasing horse power, and decreasing overheating by gutting the muffler or installing a new one is very intriguing to me. So I looked under my bus and saw that I have a 5+" exhaust coming off the turbo and going into the stock muffler. The tail pipe is only 4+", so with the baffles, I'm certain there is a lot of back pressure.

So, instead of taking the muffler out, cutting the top off, knocking the baffles out and reassembling, I am using a different approach (worst case is I ruin the muffler, and install a new Donaldson muffler anyway). I drilled a 4" hole in the rear of the muffler (without having to remove it) in the end panel about 3" to the left of the tail pipe muffler termination. After drilling through the outer shell end panel, there was another wall about 1" in, so I drilled that one out too. Looking inside, there is another baffle about 5" in with about a 5" hole in it allowing gasses to transfer from this cavity to the next one. I can also see where the 5" inlet pipe terminates in this cavity after first going to the rear of the muffler, turning, and returning to back to this cavity (it has a bunch of tiny holes in it drilled in a spiral fashion).

The cavity I have accessed would pressurize, and the exhaust gasses would go back to the rear of the muffler again through the 5" hole in the baffle, and eventally into the tail pipe, and out of the rear of the muffler. Since I am in the process of changing the oil, I have yet to fire up the bus and see how much air comes out of this new hole, but if this works out, I plan to install a tail piece to the new hole and terminate it as the original tail piece does out the rear of the bus.

My theory is that this will cut the back pressure in half, with the exception of some balancing efficiencies not being taken into consideration (most likely the two tail pipes will not have an equal amount of gasses traveling through them but I'm almost certain about the reduction of back pressure).

As with most of my half finished projects, I will let everyone know how this goes. I should be firing up the bus this week sometime. Glennman