how much difference is there in the bore in an a14 and a15

if you overbore the engine to take the a14 pistons,that will increase the compression ratio,but if you use a15 pistons,that will drop the compression.if you want a compression drop,check the a14 head,if it's a big chamber head,these will drop the compression ratio about 1 point.you wont have any problems telling what head is on the a14,because if the a14 pistons have a small dish,it's a big chamber head.so just rebuild the a12 with stock pistons & a big chamber head.

i have a car that i picked up for $50 driveable and i took it ot to the river with some mates somewhere along the line the air filter fell of and i ran without it for about 5 hours straight so now its blowin blue and pumpin oil in to air cleaner so my two options are to ethier strip it and put A14 pistons in if im not mistaken that gives me a compression ratio of 7:1 perfect for turboing, i have a A14 motor allready its allmost as tyred as this one, what is involved in turboing ?
or i can put a set of rings in give it a hone and fit my A14 head what do you guys think