Sorry thats incorrect, i'm only answering this to keep the amount of wrong info floating around from increasing. In the US ~ B18C1 is GSR and ITR is B18C5, same way in Euroland they are B18C3 and C6 respectively(*I think, but who cares about euroland ). Now in Japan however the GSR and ITR engines are stamped the same on the block "B18C", you must inspect the head stamp to figure out which engine it actaully is. Don't let flaming red valve covers decieve you, they can be swapped for relatively cheap. The head/engine code for a GSR is P72, the designation for ITR engine is P73.

Also the orginal poster shouldn't be using the Tech forum as his personal n00b questoinare.