metal quality and build quality is far superiror on the GRP..... I have several OS motors, they are nice but they are not built as well as the GRP's....... Under harsh conditions I would expect the GRP to have double the lifespan of the V-Spec............. As well the GRP engines are identical tothe older GRP NInja's, they are not hard to tune in any way...they are excelent motors and IMHO a better engine then a V-Spec...a V-Spec may have a slight power advantage but other then that the GRP is the better motor....... I have seen way too many V-Specs meet an early grave for my tastes....