i'm replacing pistons in a b18c1 block. currently the block has what's supposed to be 81.5mm, 11:1 CP pistons. there are some #'s on the back of each piston that say "79-2". the new pistons are CP pistons as well. they are 81.5mm and 12.5:1. on the back of these, the #'s say "81-2". see my problem? do these numbers indicate the bore size? if so, are the old pistons standard bore? any and all info is greatly appreciated.

 

My 84mm CP's had 84H on them as seen below. Unless teh block was sleeved it should be at least 81mm bore. Seems kinda fishy.

 

it has stock sleeves. here are a couple of pics.


old pistons


new pistons

 

ttt

 

According to CP, these #'s DO NOT indicate the bore size. they are just used in the forging process. sure fooled me to say the least.

 

Note:

Usually that number referes to the "smallest" bore size you can cut on that forging.

Shelf pistons and forced induction pistons uses these smaller forgings coz this gives you a thicker thus stronger skirt.

 

why not just measure the old piston or bore