On the far end of the scale, this is what you can get away with. The former owner had a Mopar ECU mounted here on the flat between the heater and wiper motor... I've run this coil now through 2 summers with no ballast, a stock Mopar coil, with no ill effects. On a simple, mild, low compression street engine I see no reason for the fancy, expensive, E core and other "big" coils.