Got the ZDZ210 and w/tuned pipes and stuffed it into the 3.1xtra since it has already been wrecked because the previous engine was unreliable. I am not putting anything on the Yak that has not been run succesfully in this one. Lots more power. Still tuning but it ran way better than the other engine. Imagine seven trouble free flights in a row. The tuned pipes take a little getting used to but the pull out is much better. Thanks for the suggestions.