O.S.Speed R21-M6 Marine Engine M-Works

This is the new 2026-edition Minicars Works O.S.SPEED R21-M6 3.5cc long-stroke competition engine.
Features:

• NEW 2026: two water cooling heads are included – std volume + a new M-Works head with larger volume!
• DLC coated & balanced R21 Euro-II crankshaft with more timing
• 9-port cylinder liner with 3-port exhaust
• Piston with 3 oil-grooves
• Ceramic main ball bearing
• Reinforced “R” conrod
• 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”):

• Offshore (with gear deduction)
• Endurance (with gear reduction)
• The R21-M6 is not recommended for Hydroplanes with direct drive as its too peaky for that application and the extra possible power is not needed.

Recommended fuel:

• 12% nitro fuel with 8% Klotz Benol oil (Recin) + 4% Klotz Original Techniplate (Synthetic)
• We don’t recommend running 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-M6 vs R21-M5:

• The R21-M6 has even higher timing numbers in the crankshaft and piston liner.
• The R21-M6 has more peak power but a narrower power-band.
• The R21-M6 is the highest performance out-of-the box engine for gear-reduction applications.
• 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: 265g

Included:

• O.S.Speed R21-M6 Minicars Works Marine Engine
• RP6 Glowplug
• O.S.Speed flywheel cone
• O.S.Speed decal