Basically you have two sets of (original) exhausts, fore the 3ma1 and 3ma3
They are about the same, but with one big difference
(Top pipe is 3ma3)
A 3ma3 pipe has a slim slow angular diffuser compared with a 3ma1 pipe.
So a small conclusion
-3ma3 pipe gives a less kick in the ass feeling but it spreads the power on lower revs and will give lower peek power
-3ma1 pipe gives more peak power, but you will loose power in mid rpm
Internal diameter tailpipe is a relative good, compared with modern pipes.
23mm is proven to be correct.