HELP! Sierra 2.0 SOHC Pinto Turbo max rpm problem

Hello, we have watched so much Skoegingracing videos and read the forum, so we decided to do something like you. We have bought the Ford Sierra 1989 2.0 Pinto 74kw, also turbo from bmw 525td Garret, injectors from audi vw and so on. Before engine building we get the cylinder head off and repaird it. also we've puted the new timing belt, after that we have putted the engine together. So ;)the problem is the engine does not do more than 5000 rpm. It just a cut off in 5000 rpm. That can it be? thanks.