I've got about 4 different types of can for the Abbey made spannies on the Yam twin. on the dyno, the can on the end of the spannies made no difference at all to anything except noise.
I tried similar runs but using different chambers and agan - no measurable difference.
All the cans vary in length, internal bore size of the perforated tubing and the exit hole.
Draw your own conclusions.
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These aren't the droids you're looking for.