I ran the STS 28 in my Kyosho 777 Sp1. If you are throwing in the STS with rotobackplate or pullstart unit, you will need to throw washers under the engine mount to make it fit right. I believe I had to shim it about 2.5 mm? Anyways, with this engine you will want to gear up on the CB. I used a 16T CB. With this setup I was pulling the front wheels off the ground everytime I excellerated. You will like it. But I put the D21B back in for running at my track.