Chevy TI Ignition

Now I've read a digested this article for the 3rd time. And now I have not really a question, but more of a "what if". Here's the part of the article I'm taking about:

"As mentioned, these Transistor Ignition coils have a lower impedance across the primary terminals. Standard coils measure 1.24- 1.46 Ohms. The TI coil measures 0.41-0.51 Ohms".

The article also says that the TI coil generates a hotter spark. That being the case, why not just use a lower impedance coil to take advantage of that hotter spark? This doesn't really apply to Ol' Red, but what about the guys running with points? Or even a mag pickup dizzy from MSD?
 
TimAT said:
Now I've read a digested this article for the 3rd time. And now I have not really a question, but more of a "what if". Here's the part of the article I'm taking about:

"As mentioned, these Transistor Ignition coils have a lower impedance across the primary terminals. Standard coils measure 1.24- 1.46 Ohms. The TI coil measures 0.41-0.51 Ohms".

The article also says that the TI coil generates a hotter spark. That being the case, why not just use a lower impedance coil to take advantage of that hotter spark? This doesn't really apply to Ol' Red, but what about the guys running with points? Or even a mag pickup dizzy from MSD?
Click to expand...

For any given ON time, points closed, the coil would try drawing more current and that fixed resistance wire in there would drop more voltage, so the total spark would in fact be less.....I"m not sure what the TI resistance wire would be in ohms.....the one from the bulkhead/switch....I would imagine it's much lower value, or a piece of copper, like a HEI.....
 
Erased long boring description. Third Cliff note version below.

I have a few technical disagreements with that writeup, but the majority of it is some interesting, and if you use the old TI system, useful information.
Addressing Tim's question (and it's a legitimate question) requires a touch of boring math (but just a touch) and some simplified physics. (Those with a caffeinated drink at their keyboard might fare better.)

All right, third version. (The previous two got very long, and I erased them.)

It depends on what happens to the coil current increase that you'd get doing this. The coil energy is determined by the inductance and the current through it. If we did a rough comparison of the two coils, and assume that the more wire in it, the more the resistance, then we can get a ROUGH estimate of the inductance. Looking at the resistance numbers, it appears that the TI coil has about one third (.46/1.35, the centers of the ranges you provided) the inductance of the points coil. If the coil current stayed the same, the energy would only be 33% of the points coil. But, due to the quirky coil energy formula, if you bump up the current, the energy goes WAY up (by the square of the current: doubling the current gives you four times the energy).
So, lets try a couple calculations, assuming some reasonable inductance values for the coils. As there is a 3:1 ratio for the windings, lets assume 3 milliHenry (mH) for the TI coil, and 9 mH for the points coil. Assuming a 1.5 ohm ballast resistance, we get a peak current of 4.2 amps in the stock points system, and 6.1 amps with the TI coil. Higher amperage is good(!) for energy, until the points burn out. But, let's neglect the burnout issue for the moment. Using the coil energy formula, we get a stock coil output of 80 milliJoules (mJ), while the TI coil system yielded 56 mJ. We increased the current 45% by changing the coil, but we reduced the inductance by 67%. Even though the energy goes up by the square of the current increase, the drop in inductance swamped out the benefit of the current increase.
For those that like to tinker, and it's too late in the evening for me to do a complete new set of calculations, I've always thought a manual override of the ballast resistance at RPMs above 3000 would be an amusing experiment. The ballast elimination at higher speeds is safe for the points, and would yield increased energy for the plugs. The ballast resistance is only needed at low engine speeds, and is pure waste of weight and wattage at higher speeds. There are other issues (RPM/battery voltage/dwell time) that can be thrown in for additional calculations, but I'll leave that up for later in case there are any specific questions.
Hope this made some sense. (I'm getting a blister on my typing finger.)
 
I'm really interested in this too. Ol' Red was born with the TI system. As far as I know it still works. Wiring is all there and the TI amp, it's just all been bypassed with more modern stuff.
When I got the MSD dizzy, I pulled the original TI dizzy. The lower bushing was really worn out.
 
All this crap is amazing similar to the way old TV's worked with CRT displays and magnetic beam deflection yokes around the neck in back....two coils of wire, one for vertical, other for horizontal, making the fine lines across the screen....
AND, going from being a TV tech/shop manager/cheif cook-bottlewasher.....to a engineering aide and field service rep for a walk through metal detector company....pulse field on one side of the archway...same as a dizzy, but of course no coil secondaries, not interested in sparks, but a well damped circuit we could then interpret the moving metal as a person passed through the archway....so all that pulse current/voltage/coil inductance/on the transmit side is old hat.....we used a mono polar coil with a bi polar transmitter, and the receiver coils were counter wound, the entire 7' height of the archway....
faraday shielding, whole mess....what was funny was the signal processing on the receive side of things....today surely done all dig it alley , in them daze it was all LO pass filters and a ton of op amps....crazy....

:crap:
 
mrvette said:
All this crap is amazing similar to the way old TV's worked with CRT displays and magnetic beam deflection yokes around the neck in back....two coils of wire, one for vertical, other for horizontal, making the fine lines across the screen....
AND, going from being a TV tech/shop manager/cheif cook-bottlewasher.....to a engineering aide and field service rep for a walk through metal detector company....pulse field on one side of the archway...same as a dizzy, but of course no coil secondaries, not interested in sparks, but a well damped circuit we could then interpret the moving metal as a person passed through the archway....so all that pulse current/voltage/coil inductance/on the transmit side is old hat.....we used a mono polar coil with a bi polar transmitter, and the receiver coils were counter wound, the entire 7' height of the archway....
faraday shielding, whole mess....what was funny was the signal processing on the receive side of things....today surely done all dig it alley , in them daze it was all LO pass filters and a ton of op amps....crazy....

:crap:
Click to expand...

I saw a Vette on TV once, but I don't see the relevence here.:confused2:
 
big2bird said:
mrvette said:
All this crap is amazing similar to the way old TV's worked with CRT displays and magnetic beam deflection yokes around the neck in back....two coils of wire, one for vertical, other for horizontal, making the fine lines across the screen....
AND, going from being a TV tech/shop manager/cheif cook-bottlewasher.....to a engineering aide and field service rep for a walk through metal detector company....pulse field on one side of the archway...same as a dizzy, but of course no coil secondaries, not interested in sparks, but a well damped circuit we could then interpret the moving metal as a person passed through the archway....so all that pulse current/voltage/coil inductance/on the transmit side is old hat.....we used a mono polar coil with a bi polar transmitter, and the receiver coils were counter wound, the entire 7' height of the archway....
faraday shielding, whole mess....what was funny was the signal processing on the receive side of things....today surely done all dig it alley , in them daze it was all LO pass filters and a ton of op amps....crazy....

:crap:
Click to expand...

I saw a Vette on TV once, but I don't see the relevence here.:confused2:
Click to expand...

Total relevance, different application, that is all, switching coils with DC current....rise times, decay times, tuned circuits, damping.....all the same shit....

:smash::harhar:
 
I ran a factory TI distributor with an MSD box and coil for many years until a dyno operator said "hear that miss"? actually I didn`t but he loaned me his MSD distributor while on the dyno anyway after he modified his lower gear to fit my Bowtie race block...I ended up selling the TI and bought a dual pickup MSD distributor I now run two boxes and two coils....
 
I unnersand that a MSD box quits firing extra sparks above 3 grand...I know that back before the rev limit boxes already...that the idle and off idle running was GREATLY improved on one car I had, and for one other it made NO difference and that was the '87 vette with DPFI of course....

I used it on one other car with little to no affect.....

tried it again on this '72 here some years ago, and it did not run at ALL....

so I have to say there are other/better solutions....

IF the theory was SO great, why not used in factory practice???

:crutches:
 
I don't know about the miss the redvetteracer is talking about but when I got the MSD dizzy it had all over the destructions- MUST use a MSD 6, 6AL, or 7AL MSD box. I thought that was interesting but figured they were trying to sell their stuff. So I did a little test- the TI dizzy output was just a little bit higher than the MSD dizzy output. So I cut the connector off the MSD dizzy and wired it in to my Summit/Mallory box. Works fine.

I just hooked them to a meter on the mV scale. No idea what the numbers were. CRS. Just looking a the physical size of the pickup coils sort of gives it up.
 
big2bird said:
69427 said:
I have a few technical disagreements with that writeup...............
Click to expand...

Mike,
I would be more interested in any errors you found.:crap:
Click to expand...

There were a few items I thought could have been handled better. Whether there was a lack of technical knowledge, or perhaps the writer chose to phrase things in the popular terms of the day, despite the technical inaccuracies, I don't know.

1) "....a hotter spark at high RPM ranges when the spark plug voltage requirement is higher." I'm unclear what they are saying. It sounds like they are saying that the arcover voltage is higher at high RPM than lower RPM. Arcover voltage usually tracks VE, and VE usually drops after peak torque. This is one reason points systems still do well at moderately high RPMs. The coil energy takes a dive as the engine speed increases (while the dwell angle stays the same, the dwell time drops like a rock), but fortunately the arcover voltage drops as the high RPM VE (and resulting cylinder pressure) drops, helping the points system to still do a respectable job at these high speeds.

2) "TI coils differ in that the - terminal is grounded." The coil doesn't really know the difference. During dwell, the C+ terminal voltage is higher than C-, the same as a points coil. At the end of dwell, the C+ terminal is negative compared to the C- terminal, same as a points coil. It's somewhat like putting a light switch (TI) in front of the light, or behind (points) the light. The light turns on and off the same way, regardless of the switch position.

3) ..TI coils receive 2.5 - 4.5 volts, versus a standard points coil operating at 9 volts. This old wive's tale annoys me to no end. A coil (inductor) is a dynamic device, unlike a resistor which is a passive device. If you don't know what the coil is doing when you're measuring it, your data/measurement is meaningless. It's kind of like taking a 300 mile drive in a rental car. While stopping at your destination for a pee break, you start discussing the mechanicals of the car with your passenger. You look at the digital gas gauge, and it says two gallons. Your passenger says that this thing sure hauls people around well on the two gallons of gas that it contains. You patiently explain to him that the two gallons are what is remaining after the task has been completed. It is not what magically propelled you down the road for the last 300 miles. You explain to him that the full tank you start out with contained 12 gallons, not two. If you actually started the journey with two gallons, the accomplished distance would be substantially less.
Electrically, both systems (TI and points) run off 12 volts. Not sometimes, or only during cranking. Always. The only major difference is the TI system has less ballast resistance and inductance in its design, allowing for higher coil current, which generally (but not always, depending on the combination) translates into more energy to the plug.

As I mentioned earlier, the article was very interesting and informative (part numbers, etc), and particularly so I would think to those who have this system in their cars.
 
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