The S13 redtop and blacktop are basically the same motor, the blacktop simply came in newer Silvia's and 180SX's. I believe from 94 or 95 on they were blacktops. They cost more because they obviously will have less miles on them. Also, the S14's were refered to as blacktops because Nissan never used the red valve cover again. So if someone says they have a blacktop, ask them if its the S13 or S14. Or even the S15.....lol. They're all blacktops. The redtops were the first SR's to replace the CA18's.