Building an Exhaust

One of the items I still needed to build was an exhaust system. Per the rules, the exhaust couldn't extend past the rear tire, and it's opening couldn't be directed at the rider, or the salt surface. Unlike 2-strokers, you don't have to design an expansion chamber to produce power at a certain RPM for a 4-stroke. However, there are still some basic calculations that can be run to optimize length and diameter, based on RPM. Also, stepped designs can be taken advantage of.

These calculations called out for a main header pipe roughly 18-inches in length, and a diameter matching that of the stock header pipe. So I grabbed a spare header pipe, added a few inches to it, and came up with my 18-inches exhaust length. Unfortunately, this ended the exhaust just ahead of my foot, and looked rather incomplete.

So taking advantage of a stepped design, I used a piece of larger diameter pipe to bring the exhaust back behind my foot, then built a simple megaphone that attached to the end. The megaphone was rather fun to build, as I simply cut out a pie shape wedge from a piece of 2 inch pipe, then shaped the leftover piece into the cone shape, welding along the seam.

In the end, I'm left with a main header pipe to match up with my RPM zone, that is stepped up and mated to a megaphone for looks. a simple hanger is attached to the front swingarm bolt. The entire thing will get coated in trusty bbq paint, and possibly wrapped in header wrap. A few photos are shown below.

Proportions fit the profile of the bike pretty well


The header pipe actually runs inside the "stepped-up" section of pipe about 6 inches, for a total primary length of 18 inches.


Megaphone was "squashed" to produce an oval section. I might give the tip a slight slash cut.


Chris H.