O.S.Speed R21-M5 Marine Engine M-Works

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