The O.S. Engine 21XR-B nitro engine has been engineered to deliver maximum performance with minimal effort, while still being an affordable alternative for the up-and-coming off-roader. Proven O.S. technology ensures steady power. Ideal for any 1/8 scale buggy. Plus, the O.S. 21XR-B can be upgraded with many of the 21XZ-B’s parts for greater performance as a driver’s skills increase.