I know they are bigger as I had that same question... They have a blurb on the website now about how they make them. I know this is old... Did you buy the thumper exhaust? They said it would work on my piranha engine to ct70.
Sorry for neglecting this, we are redesigning the thumper for spring 2018. It will now be made from the start with no internal baffling but will have a change out end that will look like the OEM Honda style. We hope to have 3 options for the bolt in end baffle, we are looking into making one of the options a approved spark arrester for trail riding. The only problem would be the testing and listing cost with the USFS in CA, it’s not a cheap certification to do for what we think might be a low selling option.