Homemade Megaphone / cone exhausts

'To the point' advice on what fits what, parts interchangeability and simple solutions to common problems...
This forum applies to any make.
Keep your post brief. You may include 2-3 clear cropped photos (max 600 pixels wide)...
Post Reply
gsand
Posts: 268
Joined: Fri Feb 19, 2010 2:55 pm
Location: South Australia
Interests: Riding bikes.

Homemade Megaphone / cone exhausts

Post by gsand » Sun Aug 03, 2014 7:02 pm

I'm in the process of making a new exhaust system for my Shovelhead, I needed to quieten it down a lot for daily riding, but also wanted to run the pipes wide open without much effort. Plus of course trying to be unique, what better way to do it than making my own "megaphone" mufflers from scratch.

In this post I'll show you how to make your own cones from a length of straight tube. To do this you will need a length of exhaust tube, a big vice, couple of hammers, masking tape, angle grinder and some way of welding. You would get a much nicer cone by cutting the shape out of sheetmetal then putting it in a rolling machine, but that is an impossibility for most people, I am very pleased with the result of these.

First start off with your exhaust tube, the diamater of which is determined by the largest part of your cone. In my case I used 3" mild steel, 500mm long.

Image

Next you need to decide what size you are going to reduce the cone to. My cones were to be welded to 1 3/4" tube, a slip-fit and clamp on arrangement would also work, but you would need to measure and shape the end of the cone accordingly. Since I was butt welding to 1 3/4", I had to make the end of the cone that size. This is easily measured by wrapping some masking tape around the end of the correct sized tube, cutting a line through it and then transfering the tape to your larger tube. You now have the circumference for 1 3/4" marked out on the 3" tube. First image shows the differences in diamater, the is 1 3/4" sitting inside 3" tube.

Image

Image

Then using masking tape again, make 2 lines from your 1 3/4" circumference points, meeting at a point on the 3" end. It is important here to get a straight run of tape, and not to let the tape 'follow' the radius of the tube or you will get curved cuts and the cone won't pull together properly. Notice that I've used the weld seam of the 3" tube as a centre, and this section will be removed in the next step.

Image

Image

Cut to the inside of the tape line with the angle grinder. If you don't have 1mm cutting discs or have never used them, put the grinder away until you can get some!!!

Image

Image

Now you're ready for the fun part.

There really isn't any way to describe this method, but I'll try to explain! It would have helped if I took photos here but I got carried away..

First thing is to tack the 3" end together if you cut the slice all the way through like I did. Then by going up and down the length of the tube sqeeze it together in the vice. This is a long process, if you squeeze too much in one spot you will just but a big dent in it. I squeezed parts of the tube about 1" apart going up and down, each side of the cut at a time. Most of the work needs to happen at the small end of the cone, once you start to get this into shape then the big end starts to get closer together. It helps prevent marks and dents on the tube if you have a heavy rag in the vice, I learnt this on my second try!

As you work the two sides together, tack weld whenever you get the edges to meet. I was managing fine by tacking in approx 1" increments. The first 3rd of the cone is the easiest to form, as it gets smaller you have to move the metal a lot more. It is the same principle, moving it up and down in the vice pinching it in.

If the two sides have met in the centre but still form a peak, you can hammer it more flat but be careful whats on the other side of the cone you're hammering against, it's easy to deform or dent the cone and you'll never get that out. I had better luck pinching a peak down in the vice and tackwelding whilst it was being squashed. Work the tube as much as you can before you tack - once the tack is there is pretty much stays that shape.

I used a couple of aircraft hose clamps to pull the joint together in the smaller sections, but you have to be careful and continue to work the cone in the vice to maintain a nice shape. By the time you get to the last tack at the small end, you'll probably have an egg shaped section there. Don't worry, you can work that around after into a round shape.

Image

Image

Image

Image

Image

One thing that's worth mentioning is the length of your cone. If you need it to be a specific length, add some extra on to it. The reason is that after creating the cone shape, each end of the pipe has an interesting contour as shown above and has to be ground back flat (That is the unfinished cone end against a scrap of 1 3/4" tube, testing the small end diamater. Because of the cone shape, I couldn't figure out an easy way to get ends perpendicular, I eyeballed mine with a flapdisc on the angle grinder and it's acceptable.

The last part of the job is to finish welding the seam and then grind it back. Depending on how well you formed the cone there will be some high and low spots in this area. This typically isn't a problem for our purpose, the welded section can hide on the inside of the exhaust system. I fitted mine with the seam facing inwards and down towards the ground.

Image

Image

Image

The big unveil!

Image

Image


One downside of this process is that the cone won't be perfectly circular in parts of its cross section, but it is totally acceptable for our purpose. In reality if the both ends of the cone are round, you'll never notice otherwise. For a perfect cone you would have to roll it from flat sheet. You can of course buy megaphone mufflers, or cones just by themselves, however the pair of these cost me just $15 for the 3" tube.

In the next post I will show the mufflers that will go inside of theses. I have done some experiments and some simple, removable inserts significantly reduce the noise to a polite level whilst still being a straight through design, and easily removed with a single bolt.

Hope some of you can benefit from this write up.

Regards, Glenn.

Youngblood
Posts: 372
Joined: Wed Oct 24, 2007 1:48 pm
Location: North-Eastern suburbs- Adelaide

Re: Homemade Megaphone / cone exhausts

Post by Youngblood » Mon Aug 04, 2014 12:03 am

Well done Glen
8)
Youngblood

Prof
Founder, Choppers Australia
Posts: 5768
Joined: Sat Oct 22, 2005 3:54 pm
Location: Willunga, South Australia
Contact:

Re: Homemade Megaphone / cone exhausts

Post by Prof » Mon Aug 04, 2014 12:15 am

Great post Glenn... they look good too.
Chopit'nrideit... Prof

Post Reply

Return to “Fits 'n Bits; general...”