There is another factor to consider in the spark voltage and energy needed to properly ignite the mixture, and that is the A/F mixture ratio itself. It is a combination of both compression/pressure AND A/F ratio that determines the needed voltage/energy of the spark. So even a low compression engine will have times when the mixture is harder to properly fire, whenever the A/F changes a certain way.
With carbs, they tend to 'approximate' the proper A/F ratio but it will vary a LOT more around the ideal A/F ratio with a carb than with EFI. So there is a very real the benefit of HEI with any engine in properly firing the full range of operating A/F ratios AND pressures, even in low compression engines.
