if the car was indeed built correctly then we can assume that it was tuned correctly which could explain why it does not run good now without the turbo, the car is probably running very rich because the air/fuel maps and timing are setup for forced induction. however, if this kid was a total douche and lied about the engine then there is a good chance that it was never built correctly in the first place and the engine could just be ragged out from being beat up on so much, my best guess is that this is the case because 1. the guy lied to you and 2. not many people will put a whole lot of money into a D series. no offense to Honda owners but some are to quick to want to just throw a turbo on a un-tuned, un-built engine and go out racing everything they can. if I was you and had enough money I would look for a cheap engine swap to start with a clean slat.