How far can a stock y8 TB be bored?

What is the process? Wouldn't you need a larger butterfly valve? It seems like this would be a simple task on a lathe...

 

I believe only about 2-3 mill. I you taper bored it and left original butterfly in you may be able to get it up to 60mm were it bolts up to the mani.
If I was you I would just get a 60mm one off a b series, then portmatch mani.

 

Ok, thanks.