Throwing my hands up on this ignition!

Lots of misinformation here....
- HEI coils don't get hot but the big Accel yellow coils get hot because they put out a big spark. [ someone said in an earlier post ] HEI coils run cooler because the module has variable dwell; dwell [ current on-time ] is reduced at lower rpms because it is simply not needed to saturate the coil. Therefore the coil runs cooler. The Accel coil gets hot because they were used primarily with points & had a lot of dwell time [ current flowing ], which causes them to run hotter. The temp of the coil is not a guide to it's performance. In fact, the HEI E core type coils deliver more primary energy than canister type coils because [a] the pri resistance is lower & therefore more current flows & the E core is faaaaar more efficient at transferring energy from the pri side of the coil to the sec side. Hence, their widespread use today.
- Not all MSD boxes are CD. The MSD 5 box is inductive ign.
- A CD spark is hotter & has a higher energy content than an inductive spark. Where the CD spark lacks is in spark duration: 1/10-1/4 as long in time compared to inductive; & sometimes this is not long enough to ignite a low speed contaminated mixtures [ it needs a long duration spark ]. Result is misfire. MSD found this when developing their CD igns. So some bright spark [ pardon the pun ] at MSD said; 'We will make it multi spark'! So an engineering failure was turned into success with marketing hype.
- It is the heat in the spark that causes ign. The voltage is merely the enabler: voltage needs to be high enough for air to be ionised [ made conductive ] & current to flow across the gap. In electrical engineering, the heating effect is related to DC current flow.
- As Phil Jacobs of Jacobs ign said, you never want to trade current for voltage. Yet 60,000 volts in the coil advertisement sounds more impressive than 0.3 amp, so guess which coil the mugs buy???
- The amount of voltage to ionise the gap depends on many factors. A test done by Circle Track in Aug 94 on a 9:1 engine fired a 0.050" plug gap with 28kv. A NA engine, even with large plug gaps, is unlikely to ever need more than 35kv, so a 40kv coil gives a nice reserve cushion. Going higher on voltage just trades current for voltage, a bad move because it is the heat in the current that ignites the mixture. More current=more heat.
- Ign coils are full of compromises. Example: more primary inductance is good because it transfers more energy to the secondary side of the coil, to be delivered as a spark. But more pri ind also takes more time to saturate, so that at some rpm point, it will not reach max current to transfer to the sec.
- GMs HEI levelled the playing field in ign systems, bridging the gap to CD.