just joined, have a 1988 Scarab Concept, 454. Last season boat ran 58 on gps with stock motor, 23 mirage prop. After season I pulled the motor and a very reputible local engine builder upped the compresion, added a different cam, roller rockers, performer intake. My total timing is right, jetting seems good. The boat come out of the hole much harder, the rpm went from 4600 to 4800 WOT. Running the same 23 the boat now runs 52 on the same gps. I'm baffled, the engine builder is confused, the prop guy says that this ammount of slip is nearly imposible and suggests an engine problem, but the boat runs so good, what gives! The engine builder says that the cam is right, no doubt. Any help would be apreciated I'm running out of good ideas!