049 engines run well on a 5×3 to 6×3 prop. A 5.7×3 APC works well. To get any suitable speed for mouse racing a 4-inch pitch prop is required at high revs but to do this plenty of nitro-methane is also required, for example, a 4.75 × 4 prop with 40% Nitro. Texaco engines are designed to use bigger props, e.g. 7×4.