Shift+drag the new edge loop out as far as you want – we will come back to that part later. Next we are going to define the tips a little more.
Loop select this edge and scale it so that it gives the join a little more definition (Fig.15)
Then you want to chamfer these edges, as seen in Fig.16.
Let's give the inside of the tip a little bit of detail. Select the end edge loop and use the extrude function with something like the settings shown in Fig.17.
Then go into the left hand viewport again and press F3 to toggle it to wireframe, then Shift+drag that edge (Fig.18).
You can make it look however you want. I made mine look like this using a few Shift+drags, as well as the Scale function. I then chamfered a few edges to add some definition to it (Fig.19).
Now we are going to detail the rest of the muffler. So collapse the symmetry modifier by right clicking and converting to editable poly. Then we need some more sub-divisions down the length of the muffler so make those cuts (Fig.20).
Select the end loop of the muffler, as shown in Fig.21.