Not a good idea to rapidly close the throttle with a GTSIO engine, for OEI flights.
This, over time, will cause de-tuning of the bifler pendulum dampers (counterweights), will wear the bushings on same, and eventually could cause one to be chucked out the side of the case, completely ruining your whole day...
A much better idea is to close the throttle slowly to just below the zero thrust condition, then carry out drills, as needed.
IF it is absolutely necessary to cause a rapid power loss, move the mixture to ICO, and leave the throttle where it is.
Then, follow thru with closing the throttle, simulate feathering the propellor, advance the mixture, and adjust to zero thrust.
Be kind to your engines, and they will serve you well.