Well, I finally cracked a ring land and sent my GSR block to the shop for a rebuild. The stock pistons and rods will be replaced with CP pistons, Eagle rods with a bore of 81.5. Since I'm due for an emissions test once I get everything put together. I plan to just run all motor with the stock P72 ECU and probably not put the turbo set-up till next summer. Just need to know what is the lowest compression ratio pistons I can put on there while still have a good running all motor set-up with the P72? I will be using the stock GSR head, Skunk 2 Pro Series intake manifold and stock injectors. I was thinking 9:5 or 9:8 but not sure if running a lower compression set-up will have adverse effects on passing emissions and if the P72 can even run a lower compression set-up. I do have the Hondata S300 but would much rather use the tuning costs towards turbo tuning so if I can get away with using a stock ECU that would be great.