More is better..... as long as you have a way to direct the airflow over the rad and don't cause a huge airflow restriction for high speed when the fan is off. I have found that most time at the track the fan is on when you are in the pits after coming off the track.... and having a way to keep it running is more important than the actual fan.

Make sure you seal up the fan intake area and remember to keep an eye on your oil cooling. Oil cooling has a big influence in a rotary.....