Originally Posted by Snoopy

which b18c are you referring to? there's the itr b18c and gsr b18c. the itr b18c and b16 do share the same pr3 casting. the gsr b18c has a p72 casting.

differences include different bolt patterns on the intake side, pr3's have a bigger combustion chamber, different valve angles. they're both the same physical size.

they're stamped either pr3 or p72 right above the exhaust ports