Re: TFI and HEI what\'s the difference?
For the little Jeep first...
I have a switch on the dash (have the HEI module there too.)
Flip the switch, go from HEI to DuraSpark without missing a fire sometimes...
(Watching on the laptop if I got a mag trigger and no coil fire)
DuraSpark factory resistor wire on the DuraSpark module,
No resistor wire on the HEI.
Diodes on both to keep from back feeding current either way.
I figure with resistor wire in place, and a stock canister coil, I'll get a better idea of what most of the readers are dealing with.
When I start collecting data with an E-core coil, I'll drop the resistor wire, or maybe test with it in place, then drop it...
Don't know yet, just have to see....
I have been doing silly stuff, like getting into a good pull on a hill and switching ignitions, or during a highway pass and switching.
Interesting results, somewhat confusing, but interesting.
The coil spark energy breakdown on the little jeep is probably the ignition coil, and the current reaching it. Small wires, resistors, age, Dumb****astan construction all lead to problems, and DuraSpark module (also discount store cheepie) breaks down about 1,500 RPM with total failure about 3,700 RPM.
The HEI isn't much better, spark energy breakdown using it to fire the same everything else is about 1,700 RPM with total failure about 5,700 RPM, but that's with no load.
I wouldn't be a bit surprised if either of them couldn't get the fire lit reliably beyond 3,000 RPM.
As for the MSD, you pretty much made all my points...
Multi fire in the RPM ranges most of us drive in, so full benefits...
Mine have been working fine for over ten years (probably more like 15) and I trust MSD.
With at least 600 volts going to the ignition coil, saturation times are at least 50+ times faster.
12 volts Vs. 600 volts is no contest in saturation times.
Standard 12 volt inductive ignitions are limited by saturation times, PERIOD.
They simply can't sustain reliable spark energies past a point that is about 1,500 on the standard V-8, a little longer (more saturation time for less cylinders) for 4 bangers or 6 cylinders, but around 1,500 RPM is normally when spark energies start to suffer.
MSD removes that obstacle, saturation times are faster than discharge times, so the little CD module has removed that problem.
Now the problem becomes how fast can you discharge the standard ignition coil...
It has to discharge before you can fire it again... And that is the limiting factor now instead of saturation times.
It really isn't a problem, when you can fire the plug 6 times in the span of time factory ignitions fire once, if at all...
Also, with 600 volts hitting the coil, you get MONDO more amperage!
The spark energy is so much fuller and richer (to borrow cooking terms! I am a fat guy after all...)
What you may want to watch is the time between MSD firings.
With the basic laws of thermodynamics, if you can fire the plug a SECOND time, or a THIRD time fast enough, you can take advantage of the heat 'Trail' left by the firing before.
(I can't think of the proper term for the residual heat...)
The first fire gets the area up to (and beyond) flash point, and if the second firing is fast enough (and MSD is) the second can take up where the first one let off,
IE: much shorter time to flash point than the first firing...
Not to mention MSD throws enough amperage at the gap to knock you off your feet, and it will fire a plug in a cup of oil.
(I've tried it, you can!)
With the heat and ion trail established, and so much more amperage going to the plug, the second and third, and fourth and fifth....
Firings are almost completely sustainable flash point burns, where the first one (and the ONLY one in a 12 volt inductive ignition) is almost entirely consumed just heating the flame channel up to flash point...
Let me ask you this...
Why do Supercharger manufacturers, CNG, LPG & other gas kit manufacturers, Alcohol conversion kit manufacturers all recommend CDI modules if not MSD ignition modules by name?
The fact of the matter is, Gasoline is the only fuel you can fire with a standard 12 inductive ignition even remotely reliably...
You can't even fire kerosine unless the engine is above 200 degrees (water temp), and that's gasoline's closest cousin!
Remember the old tractors and Ford cars and Trucks that has a gallon tank for gas to start the vehicle on, and a main tank for kerosine?
They usually had louvers in front of the radiator to block air flow so you could heat the engine up to kerosine temperature faster...
Ever worked on a mulit-Fuel engine?
Why do you think that when you switch over to kerosine the ignition switches off?
It's worthless, it isn't firing squat, that's why...
With MSD on the new military scout vehicles, they can reliably burn gasoline, kerosine (jet fuel), diesel, bio-diesel, alcohol and just about anything else you can pour in the tank!
(I've heard they can actually get sugar water to fire, the holy grail for multi-fuel engines...)
It's not your basic 6 series module, but the internals are pretty darn close!