Animation of Two Stroke expansion chamber:
As the pressure wave reflects back, it has a similar effect to turbocharging or supercharging a 4 stroke- it rams fuel and air that leaked into the pipe back into the cylinder under higher pressure, causing the motor to have more power (more fuel & air = bigger bang). That's a very loose explanation, but there you go.
I've always wanted to build an expansion chamber... This is where P.O.J. (pronounced Podge) comes in. This Piece Of Junk was (and is) my first motorcycle... found it in a grain bin around '95, back when I wasn't allowed to have bikes. Somehow, this one snuck home. I dug it out of storage a few years ago and began this process, so follow along as I make mistakes and learn a thing or two about building your own expansion chamber!
Please note, this is NOT the only way to do this. I think there is an easier way- done by cutting out two sheets in the correct shape, welding the edges, and the pumping ultra high pressure water in to "expand" the pipe, but I didn't have the tools at the time to do it like that. This is just how I did it...
Step 1: Equipment, Skills, and Supplies.
Skills you should have:
-Ability to Weld
-Ability to mark & cut metal ACCURATELY
-Understanding of and ability to use Shears, Brakes, and other metalworking tools
-Safe work ethic
-Understanding of 2 stroke engines
-Ability to use expansion chamber design software (OR, be really good at math or want to build 50 different pipes (trial and error))
-lots and lots of TIME
-Cold Rolled sheet metal- I used 18 gauge
-LOTS of welding rod- I used a 110v wire feed welder
-Rubber stoppers for isolation mounts
-Misc. nuts and bolts for mounting
-Duct Tape, shop towels, and band-aids. You never know!
-Safety equipment- safety glasses, ear plugs, gloves, etc.
-Measuring & Marking tools- marker, scratch awl, steel rule, dividers, etc
-Electric shears or aviation snips
-Hammer (ball pein works great!)
-Stake table with appropriate stakes
-Box and Pan Brake (could just use stake table but...)
-Welder (something capable of welding thin metal!) and related supplies- wire brush, clamps, gloves, helmet, safety gear, etc.
-Hack saw or metal cutting Band Saw
-Drill or Drill Press & drill bits
-Grinder and/or file
Other Usefull Things:
-2 Stroke expansion Chamber Software- I used 2 Stroke Wizard by Build and Click. Cost $20.00, came with a 4T header design program and a cone printing program that breaks large cones up to fit on 8.5x11 pages you can cut out and tape together. Great program. I tried a few free ones, but the first attempt at making a pipe from those didnt work so well...
-The Book Two Stroke Performance Tuning by A. Grahm Bell (apparently, not THAT A.G. Bell...)
-Someone who knows what they are doing, so you can ask questions! In my case, that was advrider.com