If you have a gsr right now, swap the head with a b16 head. Should be a perfect fit, i think, but the b16 head has a smaller combustion chamber and will bump up your compression very slightly. The b16 heads also flow better than the gsr's. Type r head is a b16 head thats been port and polished. b16 head on gsr block is called a poor mans type r setup. hth