Is this the old efficiency v effectiveness debate?
If you want to increase the efficiency of the motor, do anything that helps turn all the available energy into motion, and not heat. When the power going into the motor is just turned to heat, it reduces the efficiency. The suggestions above on timing, etc. do just that.
However, no prizes are handed out for having the most efficient motor! Prizes are awarded for the person who most effectively gets their car to do more laps than anyone else! To make your car effective around the track might mean having a less efficient motor, but then again it is probably more to do with having a good chassis (handling and roadholding) and being godd enough to get the best out of it - having the most effective car.
Whatever the maths of it all, the question remains which is the quickest car/driver combination. I can hand my car to a better driver, and he will be more effective than I am over a race distance. He might change the motor settings to get more from his driving style, and he might make the motor less efficient as a result - but he'll still take home the cups and I won't!!
The question is - why do you need to make the motor more efficient? Then we can get you some answers, only a few of which might relate to the motor! HTH