Does anyone know what the physical (internal) difference is between the two?

 

considering its alot smaller for the TRD, the stock one has 4 chambers(correct me please). i forget where i put the pic of the cutout but it does the job for making the car quiet.

and its been posted also with regards to how much TRD give you in terms of performance. end result as always is your better off getting aftermarket.

 

Muffler cut-away: http://www.precisionmuffler.com/44880e00.jpg