called an H pipe - or an X pipe - on cars used to take the bark out of the exhaust and depending on which snake oil exhaust sales guy you talk to -a power enhancher-- My 65 Nova with warmed over 327 needed em to hold down the noise my 350 truck did not - no two into one setups for me- I have two of em in a box wanna take em? good for 100cc and 160cc.