I usually test an HEI by setting it up on my bench and spinning the shaft by hand. I always get a robust blue spark. Just for fun I like to slowly increase the gap from the coil button to my ground and see how far it will fire. At one foot the spark is like a lightning bolt and I begin to fear it will choose me as the ground so I stop there. My point is the spark gets stronger the farther the ground is from the coil. The HEI coil is capable of incredible voltage and I have never had firing issues using .060" plug gaps on all my low compression motors. Of course compression, fuel/air ratio, etc all play a part but my totally stock engines are always set at .060" with no issues.