O. S. Speed r2105 is a factory-tuned engine solely developed for 1/8 racing competitions. The new engine boasts a 9-port piston liner to improve torque in the low-middle power range. It produces enough power as designed even in high traction tracks. The redesigned crankshaft counterweight enables a smooth power transition from low to top. The carburettor is based on 21m, which was well received in r2104, the main needle was changed from one o-ring to two o-rings. This stops needle change while running the engine, making it ideal for long races. In addition, the idle adjustment valve has been changed to have more torque coming out of the engine.