Muffler for an 8.1?

04GMC8100HD · August 6, 2003

What is the configuration of the factory muffler on the trucks with the 8.1? Is it singie in single out, dual in single out, or something else?

Randy

8100HD · August 6, 2003

dual in/out, I went with the Flowmaster cat back on my 8.1 includes a 50 series big block muffler dual 3" in and single 3" out no loss of low end torque.

ShortCrew · August 6, 2003

Dual 3" in, Dual 3" out. After the muffler, the two pipes quickly merge into one 3.5" pipe which is the tail pipe.

Magnaflow makes a muffler thats dual 3" in, single 4" out. This is what I used. I cut the factory pipes at the stock muffler entrance and slipped them into the Magnaflow. On the outlet, I got a smooth transition piece that goes from 4" down to 3.5". I then cut out the y-pipe after the muffler and connect the factory tail pipe to the reducer on the back of the muffler with a 3.5" mandrel u-bend cut to fit. The sound is very very mellow and deep. No noise in the cab with the windows up. If you do a search, I posted some pictures of the muffler installed about a month ago

Flowmaster makes a muffler similar in dimensions to the Magnaflow described above. Many people speak highly of the sounds they get from the Flowmaster as well.

awdvkd · August 6, 2003

Magna flow also makes a dual in (3 in) dual out (3in), I used 2.5in dual tailpipes. Slips right in where the original dual in and single out was. Any good muffler shop can make the tailpipes. Worked well and no loss of power, sounds better than the dual in single out. Quiet at idle loud WOT. Gets louder the older it gets. My 2cents.

04GMC8100HD · August 7, 2003

I ordered a flowmaster p/n 530513 yesterday. The guy at flowmaster said it was made just for the 6.0 and 8.1's, and it's dual 3" in/ single 3.5" out.

Randy

Nikto · August 14, 2003

If you have access to a GOOD muffler shop, have them make a dual exhaust setup for you.

Leave the stock muffler and right side tailpipe on and have them fabricate a leftside pipe for you. It give the stock muff a great low tone.

8.1 2001 HD.

CMNTMXR81 · August 14, 2003

FYI, they are dual CENTER inlets, and Dual outlets. The outlet closest to the passenger side is OFFSET up. From there it flows into the tailpipe collector and out the tailpipe.

I did mine LONG before anyone had aftermarket systems out, so I had to improvise some. I have two Magnaflows stacked on end next to one another. The one closest to the drivers side is center in, center out. The one closest to the passenger side is center in, offset up out. From there I originally had it go into the stock collector/tailpipe and out the right behind the wheel. It was too "poppy" sounding, so soon after I completed the true duals by removing the stock collector/tailpipe. The right muffler exits out behind the right wheel and the left muffler has it's own fabricated pipe that works it's way out the driver's side behind the wheel.

The stock muffler probably sounds ok when it is uncorked of that collector/tailpipe, but there is no comparison to what it sounds like with Magnaflows (or any other hi-po) muffler.