O.S. R21 3.5cc On-Road Club Racing Nitro Engine


O.S. have introduced the new R21 3.5cc on-road club racing nitro engine. The R21 is based on the Championship heritage of the R2102 engine and delivers an unbeatable blend of power and value for 1/8 on-road racing. Its crankshaft and piston/liner are designed with premium performance and easy maintenance in mind, which makes it an ideal choice for beginners. This engine is upgradeable with high-performance O.S. Speed parts, letting you realize your full winning potential.


  • The perfect power plant for rookies and club racers.
  • Newly developed crankshaft and piston/liner with the capability to upgrade later to a Spec-class performer.
  • RP7 Turbo glow plug.
  • 8.5 mm carb reducer.
  • Speed flywheel collet.
  • Exhaust seal ring.
  • Dust cap set.


  • Displacement: 0.213 cu in (3.49 cc)
  • Bore: 0.633 in (16.08 mm)
  • Stroke: 0.677 in (17.20 mm)
  • Practical RPM: 4,000-44,000
  • Power Output: 2.71 hp @ 32,000 rpm
  • Weight: 12.35 oz (350 g)
  • Includes: RP7 Turbo glow plug, exhaust seal ring, 8.5 mm carb reducer, dust cap set

O.S. Engines