Hi, I have a fully build B16 with 84mm bore.
My question:
Do i need to mashinate the combustion chamber on my head to 84mm also or can i let it with the stock bore?

 

You do not need to open up the combustion chamber to 84mm,unless you want lower compression.

 

So i can put the stock head with it?

 

Yes,unless you have custom pistons with a wider dome.If theyre off the shelf 84mm high compression pistons than you might need to widen the chamber,but ive never had a problem with the stock chamber on 85mm 15:1 pistons.

 

I'd open up the chamber to the bore. Its going to help the flow of the head. You wont be adding much ccs to the head, plus by going with the bigger bore, you've raised your compression already. Having more airflow is worth the minimal compression loss.