Yes and no. the YS 115 WS ( Warbird Special ) is simply just the evolution of the .91 FZ but has the compression reduced for high nitro use and has been balanced to run in the 10K range. It kind of funny to be needling the engine at full throttle and see the vibration reduction as you bring it into the correct rpm range. Even without those two relatively small changes the YS engines come closer then any other 4 stroke with their unique supercharging and close to mechanical fuel injection. It takes a great deal of power to spin a 14x13.5 at 10K. I tried for years to keep up with the YS guys with hopped up 2 strokes and finally gave up.