I know I may get slammed for this cause a lot of drag strip guys are Shafiroff guys. I've never been around the drag strip much so my experience is only from Pro Stock (and up) mud racing. Our motors are 632, & 706's and are on kill mode every race every pass. Schmidt owns mud racing and his motors hold national records. I have never seen a Shafiroff motor win a race. They're good motors and last, they just don't win. This is just my opinion and probably have not seen very many Shafiroff motors although my heads we originally done by him, but they had a lot more work done by SVRE.