In this tutorial I will show you my work flow for creating a twin tip exhaust pipe like the one in Fig.01.
I will be using 3DS Max 2010 but you should be able to follow in pretty much any other 3D software. We are going to start from the tip and work our way across the muffler. First off we will need the front viewport and we want to draw a circle spline and give it a suitable radius and number of sides. I gave mine 12 sides as I am going to use 2 iterations of turbosmooth later and I want it to be smooth. (You can use as many or as little as you want).
Move one circle to the left and clone it to the right so that you can see how the twin tips will look (Fig.02).
Create another circle with twice as many sides as the ones before (you will see why in a minute) and then squash it a bit so it looked like a muffler. These circles are going to be our blueprints for our exhaust (Fig.03).
Next we want to create a tube with the same amount of sides as the smaller circle and position it in the same place (Fig.04).
Convert it into an editable poly and then delete the back edges so that you are left with a flat circle of polygons. Make sure they are in the same place as the circles (Fig.05).
Next we want to set Max up so that it will snap to the vertexs. So across the top of the command panel right click the Snaps Toggle button, which looks like this (Fig.06).
We then want to make sure that only Vertex is selected. Once you have done that make sure that the Snaps Toggle button is on and then we can start some editing. What we want to do is go around moving the outer vertexes towards the larger circle until they snap to the position, as seen in Fig.07.