you're about a .5" raised bathtub shape on yours? if so 9.3:1 acording to what other have said about mine. Can someone post (or email me) with the height of the piston dome for different compression ratio pistons for 121ti head?? I am in the process of taking an engine apart and it's got some nice 0.5mm oversize pistons that look pretty fresh and the dome is pretty good size. I'm thinking they're "ti" pistons (9.3:1 ??) but they could be tii!!!!