The 23 ccm engines on stock 1/5 cars has about 6:1 gearing, but 3:1, even if it is a 49 ccm engine, would be too much i think. I don't know the top rpm on your engine, but i think it will get a uncontrollable top speed with lack of torque. When i was constructing my first car i used a 36 ccm chainsaw-engine and 3:1-gearing, this made the clutchbell turn blue and the clutch shoes to glaze, and the theoretical top speed would end up at about 130 km per hour. I am older and wiser now