I am not sure how to address this. What is the diameter of the holes on the engine block of a 91 N/A for the exhaust. Can you point me in the right direction as I have searched with no luck.
Thank You in Advance

 

While I'm not sure if this is the right size, I know that RB's Road Race exhaust is 2.5" per port, and I think it's that size on both ends, so I'd go w/2.5"

 

I have a mindtrain header and the outside diameter is 2.5 that goes against the block and the inside is 1.75 or a tad bigger. Just want to make sure that this is for 86-91 or is a 1st gen. Or I will have to port out a little.

 

Wow, for some reason, I'm confused, because I just double-checked RB's site, and its' 2.0" OD, so not sure where I got the 2.5" OD from...