Heres where this gets weird, because of the higher dome on the p30, putting them into a ITR bock will yield a slightly higher compression ratio, stock CR is 11.1:1 now with p30 it goes to 11.3:1 this is due the 87.20mm crank. In a stock b16a motor with p30's the CR is only 10.4:1 this due to the 77mm crank. In a GSR block the ITR Piston are going to yield a 11.3:1 CR while the P30's will yield an 11.5:1 CR. the higher compression due to the slight difference in the GSR head over the b16 or b18c5's