Try placing a spring, like a carburator(spelling?) return spring on the actuator. The goal is to keep the actuator shut a bit longer. Your strategy is to hook the spring onto the end of the actuator rod, down near the flapper door and then hook it some place on the motor or something to keep the rod from opening basically. I haven't had a chance to try it on a Z yet as i'm using external gates but it works wonders on supras internal gates ;-). I'll find someone local here one day with actuators that wants to try it but i think everyone is on stock turbos and stock fuel here :(
