I am building this little engine. There is a fan that bolts onto the flywheel with a shroud to direct airflow. I see different fans with different fin angles that I could by for it too. The engine was designed to only run a max of 6-7k rpm but I am upgrading it to turn almost 14k. My question is, can certain fans work best at certain speeds? I mean can the stock fan work well at low rpm but not be able to move enough air in the higher rpm range? Is there a way I can measure the amount of airflow a fan can produce?