This is the OS Engines FS-64V Four Stroke Aircraft Engine, .64 Size, with F4051 Silencer, OSM3AY00.

Features
Newly designed cylinder head is adopted along with the increased displacement
Internal capacity of the combustion chamber has been expanded to achieve a more 4-stroke exhaust sound and power feel
Comes with an F-4051 silencer
Drive washer has been changed to a machined aluminium keyway type
Additional standard equipment is a set of lock nuts that prevent the propeller from coming off

By increasing the stroke, not only propellers of 12x7-8 and 13x6 sizes, but also propellers with large loads (13x7-8, 14x6) can fly lightly without losing power.

A newly designed cylinder head was adopted along with the increased displacement. The internal capacity of the combustion chamber has been expanded to achieve a more 4-stroke exhaust sound and power feel.

The F-4051 silencer, which is a unique design of the V series, has revised the internal dimensions and improved the exhaust efficiency while maintaining the comfortable 4-cycle sound.

The drive washer has been changed to a machined aluminium keyway type. A lock nut that prevents the propeller from popping out, which has a proven track record as a safety measure, is standard equipment.

Specs
Displacement:10.46cc
Bore: 25mm
Stroke: 21.3mm
Output: 1.14ps/11,000r.p.m.
Practical RPM range: 2,400～11,000r.p.m.
Propeller size for sport/Stunt: 12×6-8 or 13×6-7
For Scale: 14×6
Weight: 442g (engine), 44g (silencer)