O.S.SPEED R21-M5 M-Works Marine Racing 3.5cc Engine
This is the new 2026-edition Minicars Works O.S.SPEED R21-M5 3.5cc long-stroke competition engine!
Features:
- 2026 Update: New M-Works Larger Volume Cooling Head with Stainless Nipples
- Combustion chamber with smaller volume for low nitro & updated piston for easier run-in
- DLC coated & balanced "SG-type" crankshaft (4.5mm balance weights)
- 9-port cylinder liner with 3-port exhaust
- Backplate with steel thrust plate for lower friction and increased durability
- No carb included - choose your own carburetor (15mm diameter neck)
Suitable for competition boats (experience level ”high”):
- Hydroplanes
- Offshore (with gear deduction)
- Endurance (with gear reduction)
Recommended fuel:
- 12% nitro fuel with 8% Klotz Benol oil + 4% Original Techniplate
- Don't run the engine with less oil than the above recommended levels. You may add more recin/castor oil (Klotz Benol) in extreme conditions and heavy loads.
Performance R21-M5 vs R21-M6:
- The M5 has normal high timing numbers in the crankshaft and piston liner - the R21-M6 has more timing everywhere (more peak power but narrower power-band).
- The M5 is the highest performance out-of-the box engine for hydroplanes with direct-drive (2025 iMBRA Hydro World Champion).
- In Endurance and Offshore, the R21-M5 is easier to set-up as it's less peaky and have more torque vs the R21-M6.
Specs:
- Displacement: 3.49cc
- Bore: 16.08mm
- Stroke: 17.2mm
- Crankshaft dia: 14mm
- Practical r.p.m. Range: 4.000～43.000
- Output: 2.76hp @ 35.000r.p.m.
- Weight: 256g
Included:
- O.S.Speed M-Works R21-M5 Marine Engine
- RP6 Glowplug
- O.S.Speed flywheel cone
- O.S.Speed decal
9-port sleeve with a 3-port exhaust
DLC coated crankshaft with improved balance
Steel insert backplate for less friction and more durability
New M-Works water cooling head with larger volume
Combustion chamber with smaller volume for lower nitro levels
