HEI ignition conversion

[nkemp]

So this thread got me interested and I came across this. Adding to this thread as FYI for those interested.

The Popular Hot Rodding site made the following points:
- Some skip this step but good practice is to coat the bottom of the module with silicone dielectric grease for insulation and a bit of thermal transfer. The module NEEDS to be on a good heat sink.
- Some folks use heat transfer paste (like used on PC CPU's). Trouble is that it could dry up in hot underhood conditions. Depending where you install in the D, this may not be an issue. If mounted in the original spot, engine heat will not be an issue relative to drying the thermal paste. The question is ... does it get hot enough by itself to dry the thermal paste?
- Silicone/dieletric grease will not dry up and works well in hot environments.

[stevedmc]

Can you show how this gets wired with the correct coil and without the resistors (I always hated how they look)?

Steve Rice, Farrar Hudkins, Byrne Heninger, and Bill Robertson among others are running HEI wired like this:



The key components are not the ignition module, they are higher coil input voltage, a high ratio winding coil, and much wider plug gaps. Without all of these you will not have HEI, no matter which ignition module you are using.

Steve Rice and Farrar Hudkins are using stock Bosch ignition modules with their HEI. Byrne Heninger and Bill Robertson are using Ford Duraspark ignition modules with their HEI.

Some owners have eliminated the ballast resistors altogether. Wiring the resistors in parallel cuts their resistance in half and increases primary coil voltage to 12-13 volts while the engine is running. Coil input voltage while cranking is same as stock, but the resulting spark is higher due to the higher winding coil and the wider plug gaps.

[Raphael]

yes of course, in addition I already have a MSD Blaster II coil and running wider gap on the plugs, and 8mm wires.
I kept the ballast resistor as long as I used the stock ECU, but now with the GM module, I think I can cut half of the resistor. I would like to get totally rid of it, but not sure if it's safe for the MSD coil. some say it can handle full voltage coupled with a modern ECU, some say no.
reducing voltage on the coil kills most of the benefits of a good coil.

and of course, the GM module MUST be installed on a heatsink with specific compound. ( it comes with the module when you buy it).
the title of this thread says "HEI" because the module itself is commonly referred as a "HEI module" at GM. Technically, a true HEI setup is a hi-voltage ignition using a modern coil like MSD or Pertronix.
the point here , was to offer an alternative to the stock ECU with obsolete electronics. the stock bosch unit works great for a 30+ years old device, but it's becoming oldish.
i like the features of modern electronics like the smart self-adjusting dwell. so your HEI coil gets full saturation at any RPM

[stevedmc]

Byrne Heninger's Bosch ignition module died, thus his upgrade to Ford's version of HEI, so yes indeed: OEM ignition modules do not last forever.

[Raphael]

I just received a reply from MSD Tech support, they confirm that we can get rid of the ballast when using a modern module like the GM HEI.
of course the ballast is still necessary when running the stock ECU.

[stevedmc]

Actually the resistors are there to protect the Bosch coil, not the ignition ECU. A stock coil can not handle more than 8 volts for extended time.

Owners running both resistors in parallel (.25 ohm, 12 volts into the coil) with a stock ECU have no problems.

Byrne Heninger's Bosch ECU died while he was running stock ignition.

[nkemp]

So If I understand this correctly the resistance is there to protect the coil (by reducing the voltage to the coil) and resistance also determines the coil output voltage. For example, the Pertronix coil has built in resistors and depending on the coil as the internal resistance goes down, the voltage goes up. As such, including the resistors in parallel like shown above is reducing the coil output voltage.

The Pertronix coils are:
- 40,000 Volts DC 1.5 or 3.0 Ohm primary resistance (not clear why 2 different resistance values generate the same voltage... but it is all internal so there may be more to the design story)
- 45,000 Volts DC with .32 Ohm primary resistance

The Bosh coil must not have built in resistors which is why the firewall resistors are there. Running the resistors in parallel (reducing the resistance) causes the Bosch coil to throw a higher voltage spark than the series design.

Also, actual resistance used must be a function of the coils voltage design value. For example one coil could be designed for 12 VDC and another 13VDC and if so, the resistance values would be different.

The resistors are not needed for the control module operation.

Did I get that correct?

[stevedmc]

Do not increase primary voltage into a Bosch blue coil or you will burn it up. Only increase voltage into a coil designed for it, such as Pertronix or MSD.

[vwdmc16]

Right, im running full voltage to my MSD blaster II coil with the stock ECU and have had no ignition issues for over a year now.

[nkemp]

Do not increase primary voltage into a Bosch blue coil or you will burn it up. Only increase voltage into a coil designed for it, such as Pertronix or MSD.

Steve you also said

Owners running both resistors in parallel (.25 ohm, 12 volts into the coil) with a stock ECU have no problems.

Doesn't running the resistors in parallel increase the voltage to the Bosch coil?

I'm not trying to cross examine you ... I'm just trying to get a good handle on this and it is a car topic I never really thought about before.

Nick