O.S. Engine OS-13875 21XZ-R Ver.II Circuit Performance Unit  [OS-13875]

High Rev Performance from the O.S. Engine 21XZ-R Ver.II

The O.S. Engine 21XZ-R Ver.II, model OS-13875, brings a focused performance profile for track work, giving drivers a high RPM ceiling and steady midrange for consistent laps.

Engine Geometry and Usable Rev Band

With a displacement of 3.49cc and precise bore and stroke dimensions of 16.27mm and 16.8mm, this engine delivers a practical RPM window from 4,000 up to 45,000. That range helps match gearing to corner speed and straights.

Output Versus Mass

Rated at 2.75ps at 33,000rpm (2.79hp), the 21XZ-R Ver.II provides competitive power while remaining light at 343g, aiding cornering agility and overall vehicle balance.

Designed for Tuned Setups

The 21XZ-R Ver.II is aimed at builders who expect precise tuning and setup work. It responds predictably to needle and carb changes, making it a good choice for experienced hobbyists focused on lap consistency.

For club and circuit competitors, the O.S. Engine 21XZ-R Ver.II pairs a broad rev range with a light package, making it a solid option for tuned on-road cars.