Im pretty sure that the DR500S motor is the same as the SP500 motor isnt it? Basically because USA already had a Enduro DR500 X, Z & D, instead of calling their 500 trail version (Our DR500S) another DR, they just called them a SP. Our DR's were basically their SP's until there were a few USA spec DR's that were imported here and also later on in the 80's we had 2 versions of the DR250 and both were called DR's.