The number of turns on an electric motor refer to the number of times the wire inside the motor is wound around the magnets. Lower turns typically means higher revolutions which means higher top speed. The drawback is that the lower the number of turns the less tourque there is to get to speed. For example....Lets say you have two motors of equal quality components. One 27t (stock) and one 12t. Put them into two cars set up exactly the same with the same ESCs. Race them and you will find the 27t one will kill the 12t off the line but then hit max speed and level out very quickly. The 12t will take longer to get up to speed but once it does it will smoke the 27t like it was standing still.