In theory the tractor (8N) coil would be designed for a 4 cylinder engine that runs at low RPM while a car/truck coil would be designed for an 8 cylinder engine at higher RPMs. The difference would be the saturation time of the coil. In practice I'm not sure if there is a real difference or not, Bubba might know the answer, but something to consider. If there is a deference in the design it would mean that the coil would appear to run great at lower RPMs but not provide a proper spark as the RPMs increased.