Building a B18B to boost and go in my 91 DX hatch, which size bore do I need? Plenty of pistons out there to buy, but I need to specify apparently, and wasn't sure what the right one was.. Any help is appreciated

 

Standard/stock bore for all B-series except the B20 is 81mm.

 

So 81.5 mm pistons will not work, or will work with some machining? Also, is there any advantage to some of the 84.5 or others?

 

if you overbore the cylinders, 81.5 pistons will fit.

there's no replacement for displacement. bigger bore = more power. but those wont fit without resleeving.

 

Hey man. I don't mean to get on you or anything so please don't take offense to this, but if you are asking these questions you have a lot of learning and reading around here before you should even think about doing this. I'd hop over to the FI area and read everything you can get your hands on.

Best of luck and have a good time learning.