which ones, what will they do (raise/lower compression, anything elese)

 

any b series except b20 and b21. all of them will raise compression.

 

note that only the b16a and b17a pistons are a direct fit. the b18c and b16b pistons utilized a smaller rod end. So i you want b18c or b16b pistons in your ls (or b16a or b17a) you will have to have your rod ends machined down a little so that they will fit. Not a big deal at all, but just something you should be aware of.