The OS Engines R21 Euro II Nitro On-Road Engine features some upgrades to improve performance. To obtain more power the balance of the crankshaft was updated and now sports 3 tungsten counterweights, giving an improvement in the mid-range. Another effect of this change is the return to idle has been improved. The liner now has an additional cooling hole on the exhaust side and the crankcase has been updated to cater for this. The OS Engines Speed R21 Euro II Engine is available on its own or as a combo with the TR01 pipe and MR02 manifold.