My car has a D17 engine: 9:9:1 compression ratio and 75x94.4 bore&stroke(mm).
Now, the new civic GX model has a 12:5:1 compression ratio and the same bore&stroke(mm). Can I put those pistons used in GX and replace the ones in my car to UP my compression ratio for better performance??

 

gx? whats a gx? and d17? are these newer model civics and engines?? like 2001 and up?

 

It's their new CNG vehicle.

And to answer the original question, if you want to run that high of a compression ratio on your motor reliably you'll need more than just the pistons. Compression ratio in and of itself actually dictates quite a little bit about how other parts of the motor (such as the combustion chamber and camshaft profiles) should be designed, and vice versa. The whole top end needs to be optimized for such a large jump (2.6 points) in compression in order to work reliably and effectively.

 

They are also forged

 

forged pistons in an OE application? Are you sure about that?

 

yes the Natural Gas civics came with 12.5:1 compression forged pistons and they will fit your d series motor