I wouldn't have done it, but when I checked, it was real close to 4" anyway, and had been flying fine. This happened from removing the brass prop nut (substituting aluminum) and going to a pair of 2000 milliamp packs instead of the one, big, Nicad 2250 pack I had in there to begin with. All I did was relocate the 2000 packs from one side of the firewall to the other.