2wd flywheel is lighter than 4x4 and makes a big difference, have you had you engine apart ? Was a bought engine if the answers are you don't really know then it may be low comped which is very lazy at revving a std comp engine is actually not ba at all and for you to notice it there must be some thing a miss, and comparing it to a totally for rent engine is utterly pointless it's a different engine simple so will behave different !