Exhaust Size

[Milan]

I have 2 exhausts here. One stock.
One DG.

What a difference in diameter the stock one is.

 

[m in sc]

the id is what matters. a lot of stock pipes of that era have an inner 'layer' for sound deadening. the tzr for sure does. dont read too much into it.

[bitzz]

The stock pipe is double walled. Did you notice they weigh twice as much as the DG pipe?
IIRC the stock pipe will be better for top end.