Quote:
Originally Posted by RichardJ
from above
>>If the resistance wire from the ignition switch to the distributor is still being used then he won't have 12v. Likely nearer 7v which causes undue heat in the module.<<
Absolutely and completely false.
To begin, you should be starting with 14Volts, not 12v, assuming you have a working alternator.
That dreaded ballast or ignition resistor wire measures 1.6 Ohms. (1.8 ohms on the inline six)
If you would insert an Ammeter in the B+ wire feeding YOUR HEI, if it is an original GM HEI, you will measure 1-2 AMPS. GM actually list it as 2 Amps in some spec sheets and sometimes 1.5 Amps.
OHm's Law states; Voltage = Current x Resistance
This will give you Voltage drop across the Resistance Wire. I.E. the voltage you are fearfull of losing from the 14Volt supply voltage.
The dreaded 1.6 ohms X GM's 2 Amps = 3.2 Volts dropped across the resistance wire. MAX
14 Volts - 3.2 Volts = 10.8 Volts at the HEI BAT terminal.
In reality the stock HEI with stock coil will draw less than 2 Amps and through an original resistance wire you will still have between 11 and 12 volts at the HEI Bat terminal.
It is also true that the stock HEI when supplied with anything from 8-16 Volts will still supply adequate secondary voltage from idle to 6,000 rpm.
A points ignition and a HEI ignition are both called Induction Ignition systems.
You need to understand that the 10V or 12V or even 14V flowing through the ignition coil does not generate the secondary voltage that fires the spark plug.
12volts flowing through a primary winding of the ignition coil generates a magnetic field around the primary and secondary windings.
It isn't the 12Volt generated magnetic field that causes current to flow through the secondary winding to the plugs.
IT"S WHEN YOU REMOVE THE 12 VOLTS.
When the points open and the 12 volts stops pushing current through the coil, The magnetic field COLLAPSES. When the magnetic field collapses. it generates as much as 300 Volts across the primary winding. This voltage is called Back EMF.
Coil advertisements often include information such as a winding ratio of 100:1
300 primary volts X 100 = 30,000 secondary volts, potentially. When the 20k-30k is being generated in the secondary winding, you do not have 12 volts on the primary winding, you have 200-300 Volts.
That arcing you see across the points on a points ignition isn't the 12 volts, it's the 200-300 volts looking for a place to go. Most of it goes into the condenser and later discharged when the points close again.
The points ignition can't maintain dwell time as rpm increases. The magnetic field doesn't have enough time to be fully saturated and the 300 volt number drops.
The point closed is the Dwell time and is mechanically linked to the points open time by the shape of the lobe.
That's where the HEI comes in. It can control dwell time at higher rpm.
If you don't understand any of that above, you should stop expounding the crap about having to have a FULL 12VOLTS for the HEI.
If you're going racing that's a different story. You should know that there are circletrack racers out there that run a racing HEI without an alternator. Starting a race with 12.5 battery voltage, they still have plenty of high rpm ignition, 40 laps later when the Bat may have dropped below 10 volts.
For the street, I can tell you I installed a coil-in-cap HEI in my truck more that 25 years ago. 10 years ago when I installed the AC, I switched it to an external coil HEI. The original Resistor Wire is still in place. I read 11 Volts at the distributor. The truck gets 15-16 mpg on the highway and it can run 70-75 mph for a couple hours at a time and never skip a beat.
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Well stated Richard. I doubt that too many beside you and I understand the technical aspects, or will be able to convince many others.
The level of exasperation you exhibit equals my own when it comes to posters who forget to give details even as simple as the year of their trucks.
Points to add.
You are correct about the 12 volts not generating the 20K to 30K volts on the induction side of the coil. I believe the boost comes from the discharge through the condenser (points), or the ignition module (HEI) what say you?
You didn't address the module heat caused by low voltage but I think this is in error and the heat is caused by the engine temperature transferred through the distributor so an insulator is used. Resistance also produces heat so it may need to transfer to the distributor so either theory is possible.
It has been stated that using the external voltage regulator, which generates voltage spikes, is often the module killer in HEI ignitions since the modules do not like voltage spikes. Most digital equipment follows that rule.
Your last paragraph bears out the original post where he states that his engine ran fine until it died and again after he got it restarted.
I'm open for discussion.