The 3 port sport is a great motor for the money. ($115.00 is Map) it uses the same crank, rod,piston, block, bearings. The carb is aluminum, head is smaller and the block doesn't have as much milling internally. The sleeve has just basic cuts in it, I modded one a while back and it was really fast. I never really raced it but me and my son were on a 100x60 dirt oval playing around and he had his 5 port and I had my modded 3 port sport. It was pretty much a dead heat.

Rex