a car i just recently bought might have some engine trouble. an expert( will remain nameless) said whats happening is there is too big a gap between the piston walls and the pistons. he showed me the blow back from the valve covers and said all this smoke should be goin out the exhaust. i then would have gas mixin with the oil. the car makes decent torque but makes little HP. once i get around 4500 rpm the tach seems to die off and i cant really pick up speed. anything else it could be? hate to buy a new engine, just got the car. help please.