u very seldom see an automativer on the oval dirt or asphalt being competitive..the straight drives can have the gear wored so that it can be benefical going in the turns and coming off the turns..all the mnaul 3 or 4 speed trannys will be 1 to 1 ratio in high gear..depending on the size track you running..you may never get out of third and possibly gear down to 2nd...thats it....
go with a straight drive..it will not take as much HP to run the straight drive as well...
they do make a circle track tranny and converter..but the one shown below is for a V-8..i get the idea you may be trying to run a bomber if so go with your bomber 4 speed..if not then check out the auto tranny below..i still do not see may competitive round track winners using them however...
http://www.jegs.com/webapp/wcs/store...44272_-1_10723
good luck
Brian