Originally Posted by CroMagnum
I've never heard of expansion chambers being formed in that way. You want the dimensions of a pipe to be very precise, something not possible by pumping water in between a couple of welded plates.
Most OEM chambers are made two halves of stamped sheet metal that's been welded together like this -
And most aftermarket pipes are constructed from rolled cones and bent header pipes, again welded together -
Whoever told you that water forming fairy tale was just making things up to see if you'd believe them.
Trust me, I can't answer for 2 strokes in America but, in my racing, blown pipes are entirely ordinary, and the same applies across European countries. OK, if you need to change direction or angle somewhere you will have to cut and rotate the sections, but you get far smoother shapes far more easily than with welded up rolled sections.
There is a downside though, in that harmonic cracking can occur, where the fracture actually goes at an angle through the pipe, like glass breaks. It's effectively impossible to repair when it goes like that.
Here's the way it's done: http://www.3wheelerworld.com/showthr...ansion-chamber