Re: DIY expansion chamber?
I made my own 'patterns', although not all that accurate.
Just to get the shape.
Then worked out the 'Trig' on the angles I wanted.
measured the pipe, divided it into six, then cut Vee's of appropriate length to get 30mm to 76mm over that length. Simple really, then squeezed it all up, with a bit of a tap here and there.
and welded with an inverter stick welder.
The pipe with the stinger exiting the belly is noticeably quieter,
but I can't comment on it's performance difference as both pipes are totally different.
As is the exhaust port timming on the motors.