*organ music*
Today's second reading is from the book of Fire, Chapter 1, verses .035"-.060".
And lo,
The HEI or electronic ignitions can carry more coil primary current and switch it faster than the breaker points. The electronic ign coils are wound to make use of the extra current, and thus generate a higher voltage at the secondary (plug) winding. Thus you can open the gap wider and the higher voltage will jump the gap and produce a fatter spark.
Gap depends on plug design, voltage available, fuel mixture and compression ratio. The higher compression tends to "blow out" the electrical arc we call a spark. Its either close up the gap so the lower voltages can throw across the plug gap, or add more voltage. So thats why high-compression motors run better with electronic ignition. The cylinder pressure can't blow the arc out as easily. Rule of thumb I've adhered to is .035" for points, .045-.050" for HEI.
From what I understand, the .060" gap was specified in the late '70s to light the lean fuel mixtures in low CR engines of the time. Lean fuel mixtures and bicycle-tire cylinder pressures are why the '78 corvette had a whopping 180 HP. EGR my donkey.....
The .060" gap has been seen to cause problems above 10:1 CR. The larger gap coupled with normal wear of ign system (cap, rotor, wires, plugs) and high CR can cause misfire. The voltage at the plug wire has to peak higher to jump a .060 gap than a .050" gap. Thus arc leakage from wires and carbon tracking can shunt the juice to the block before it jumps the plug gap. Ever wonder why the race cars use 8 or 10 mm plug wires? Insulation.
can I get an amen....
