OS SPEED R21 GT II is an all-new 5-port engine. 
It features a newly developed underhead, cooling-head, crankshaft, Specially made to fit on-road GT track. 
The OS SPEED R21 GT has a 7mm carburetor restrictor.

Tech specifications:

• The crankshaft uses two tungsten counterweights. We have optimized the mass balance by reviewing the detailed dimensions.
• The inner head has been revised. Improved low and medium speed feeling and idling performance. An O-ring is also used to reduce vibration and improve dust resistance.
• The weight of the new outer head, compared to previous model has been reduced. Fins of outer head has been machined.
• Equipped with 5 scavenging ports and 3 exhaust ports to meet IFMAR regulations.
• Equipped with a double-adjust type 22E(B) GT carburetor. The new venturi is 7.0MM(RED) AL2.
• Practical RPM range: 4,000 – 42,000 rpm
• Max. power output: 2.65 ps / 2.61 hp / 34,000 rpm
• Weight: 369Gr.

With tuned pipe TB01 EFRA2042(T2060SC) and 70mm manifold