I researched this issue a few months back, you could go with JDM ITR Pistons which have a 11.1 CR rather than the USDM ITR pistons. The CTR pistons with a gsr head will be very high compression. You will have to retard timing in the ignition. Now with an Si head the compression will be .2 less. I am building a gsr block with a si head and I was originally going to go with the CTR pistons, instead I have opted over to the JDM ITR pistons which will give me a good daily driver and excellent horsepower for my application.