i use a zener diode to protect mine
buy a
VS-40HFR40 Diode
Stud mount diode,
R in name means reversed anode/cathode
Mount it into the bracket as well, and run a wire from the free end to coil negative
this stops a voltage spike on the primary side of the coil going higher than 400V
something higher than 400V will stress the ignition module
you can achieve similar protection with the capacitor that was installed originally with the module when mounted on the large HEI dizzy on a remote coil chevy I6
shown a s 1 microfarad between ground and +ve feed in the diagram above
the diagram above represents the absolute Belt and Braces (suspenders) implementation Jaguar and Lucas did on the V12 Jaguar engine in the XJS i.e they went all out and included every component they could see from the original application diagram created by motorola when they did the work for a stand alone microchip set-up that eventually morphed into the 4 pin HEI we have known since 1975. most of it was not that relevant in later years, given the fast advances in semiconductors from the 80s onwards, but that didn't stop jaguar sticking to its OEM standards from the last decade until FI and ECUs came in. A modern HEI module in theory does not need a capacitor (cars do not have AM radios and CBs these days) or the zener diode because HEIs use a different high power switching "transistor" (for want of a better word) that is more robust these days, and can survive a spike of 500V or more. But we are not using these modules as standard. our heat sink is different, our coil may be different, our plug gaps may be different, our alternators and regulators are different, our magnetic trigger is different, it can produce a lower level signal (peak to peak) and has a different resistance therefore it messes with the dwell control slightly, namely more current flow in the coil, for longer, at certain RPMs, meaning hotter coil and module.
dwell control in HEI is all about limiting the dwell to a very small value at low RPM to avoid overheating the coil and module and allowing it to float to maximum possible at Higher RPM. this is done with capacitors and resistors. and of course the pickup coil and the ignition coil are connected to that circuit and their resistance can play a part.
dwell control is based on how big the AC wave form from the pickup is
high RPM big wave with higher AC voltage
low RPM small AC voltage
impiedence plays a part the mismatch between pickup coil and module has an impact on dwell control.
And also many of these modules are made by factories that might not apply the same QA as delco did and to avoid copyright and patents certain characteristics are tweaked to make them just enough different to be thought of as unique
if they are happy to put their name on the box and the sealed baggy the module is wrapped in, its probably a decent module.
if its just rattling around in an unbranded box ....Mmmmmm no. best to spend $20 not $7
but you do not need to spend $140
Dave
ps picture below shows 1 cycle as 1 peak on the reluctor ring pases the magnetic pickup
faster the dizzy spins the bigger the peak
also illustrates why having the wires the wrong way causes the need to adjust the timing to get it to run and why the timing is totally inconsistent if the wires are backwards
runs good you have the pickup wired the correct way
runs bad.... well..... try them the other way round
instead of triggering at 1.7 volts on the upswing as the peak passes the magnetic pickup, you are triggering at minus 1.7 volts on the slow ramp of the initial down swing caused as the peak approaches the magnetic pickup, and that slow ramp gradient and therefore where it hits Minus 1.7 V (with the wires backwards) differs massively with RPM. (i made up the 1.7 v bit, i do not know the exact trigger voltage, its just definitely NOT zero Volts, and needs to be big enough not to be a false trigger AND not so high as to be too different between low and higher RPM)
