Constrictor snake (Medium) ability scores: Str 17, Dex 17, Con 13, Int 1, Wis 12, Cha 2
Improved to Large: Str 25, Dex 15, Con 17, Int 1, Wis 12, Cha 2
Oddly...
Giant constrictor snake (Huge): Str 25, Dex 17, Con 13, Int 1, Wis 12, Cha 2
So Str could fall in the 18-25 range, Dex could stay 17 like the others, and the rest of the ability scores are constant.