O.S. Engine OS-13875 21XZ-R Ver.II Race On-Road Motor  [OS-13875]

O.S. Engine #13875 - 21XZ-R Ver.II On-Road Engine
Price:
CAD$507.29
Brand:
O.S. Engine
Model:
OS-13875
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Track-Focused Power from the O.S. Engine 21XZ-R Ver.II

The O.S. Engine 21XZ-R Ver.II, model OS-13875, is built for on-road racers who want predictable throttle response and strong top-end. Its design emphasizes controlled power delivery and tunability for circuit work.

Balanced Internal Geometry

This 3.49cc engine uses a bore of 16.27mm and a stroke of 16.8mm to create a compact combustion chamber that supports a usable practical RPM range from 4,000 to 45,000. That spread gives tuners flexibility across different tracks and gearing choices.

Power Output and Lightweight Design

The 21XZ-R Ver.II produces 2.75ps at 33,000rpm, equivalent to 2.79hp, while weighing just 343g. The combination of output and mass yields an advantageous power to weight ratio for competitive chassis setups.

Set Up for Competition

Designed with racers in mind, the 21XZ-R Ver.II rewards careful jetting and break-in. It is best suited to pilots with some tuning experience who want an engine that responds well to adjustments.

Specifications

  • Displacement: 3.49cc (0.213cu.in.)
  • Bore: 16.27mm (0.6405in.)
  • Stroke: 16.8mm (0.661in.)
  • Practical RPM: 4,000 ~ 45,000
  • Output: 2.75ps/33,000rpm (2.79hp/33,000rpm)
  • Weight: 343g (12.08oz.)

For racers focused on lap time, the O.S. Engine 21XZ-R Ver.II combines compact design and strong performance to suit competitive on-road use.

What fuel mix should I start with for the 21XZ-R Ver.II?

Start with a high quality nitro fuel that falls in the 20 to 30 percent nitromethane range for performance runs, and follow the engine break-in procedure recommended by the maker for first outings.

How does tuning change handling on track?

Small carb adjustments affect throttle response and midrange. Leaning the mixture raises top RPM but can make the engine less forgiving, so tune in small steps and monitor temperature.

What regular maintenance keeps this engine reliable?

After each session, wipe external grime and check the glow head and needle settings. Perform a deeper inspection, including bearings and carburettor, every 8 to 12 hours of running or sooner if you detect unusual vibration.

Can I fit this engine to different on-road chassis?

Yes. The 21XZ-R Ver.II adapts to a variety of 1/10 on-road and touring car frames, but expect to adjust mounts, exhaust position, and carb settings to suit each chassis and gearing choice.

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