GSR= Piston Coolers (oil squiters)
Main Girdle
VTEC High Flowing Head
Kinda thin Block
Nice room for overbore.

Only thing B18C5 has different is stronger trany brace and valvtrain and cam, and pistons.

B18C is the best series to use, very versitile. B18A and B18B no squiters and thicker block no main girdle.