Engines are either an air-cooled, 4- or 6-cylinder aircraft or water-cooled, large-displacement, V8 automotive engine, ranging from 50 to over 600 hp. Automotive engines tend to be less expensive due to readily-available replacement parts and less expensive high octane automotive gas. Since an opposed, 4- or 6-cylinder (O4 or O6) aircraft powerplant contains fewer moving parts than a standard automotive engine, it is easier to repair and weighs less. However, automotive engines can be repaired by more-common car mechanics and do not require specialized repair personnel like aircraft engines do.