In changing over to elect on a size 40 plane . What is a good motor to go with .....

Depends on the plane? You can get a lot of flight time with a Tacon 32 and a 3s battery in a trainer. Yet that would barley fly a 40 size Edge, Extra, Giles 202? You would want something like a Tacon 46 with a 5s. What type of plane are you converting?

Buzz.