mesh size - number of nodes

sam

hey i want to simulate a compressor rotor. i have to solve in two way. one actual model and 2nd scale down model by 100

now my question is that in CFD wiki it says a good mesh with wall function should be 400,000 cells , so i wanna know that should i use 400,000 cells for both models (actual and scale down) if yes why and if no then also why \?????????

regards