Yes it was. It was only about three miles per hour slower than the Ki-61, even though it had a large radial. The designers looked at the Fw-190, and how a large radial was moleded to a small airframe so smoothly, and made the transition rather quickly. I believe they used the Ha-104 engine, but thats just an off the top of my head guess, or the Ha-114. Either way they were high powered, in supply and easy to maintain. The previous model, the Ki-61, was built with the Ha-40, liscence copy of the Db-601. The japanese lightened the engine and increased the horsepower somewhat, but always had maintenance troubles. Both fighters, the -61 and the -100 were respectale, but the -100 was overall better even with the incremental lack of speed because it offered better reliability and maintainability. Some -61 airframes were used, and then new ones were built to make the new -100's. The aircraft was a serious threat to P-51'a, and from reports from pilots ive read, it made the Hellcat less of a fearsome opponent.