I have been running the Yellow (140001) Supercoil for a very long time now. This was always mated up to a MP Chrome box and a factory 1.5 Ohm balance resistor.
Now, for as long as I can remember during low idle speed as soon as I would drop below about 800 RPM my AutoGauge (233905) Tach needle would swing to the 'off' position and almost always immediately return back to read running RPM.
For some time I overlooked that, it was annoying, but heck, I purchased the tach off of eBag years ago and even if there was something wrong with it I didn't have any receipts and so didn't think I could return it for warranty either.
As it happens over the weekend I was reading some on-line articles about ignition systems. As applicable to the Yellow coil there was the mention of needing to run the 0.85 ohm resistor for a points setup. Specificaly here is a quote from their Q&A posting:
Q) I just purchased an ACCEL super coil. Do I need to use the ballast resistor supplied?
A) It depends on which ignition system its being used with. When using a single or dual point distributor, coil positive should be supplied with 8-10 volts with the key in the "run" position. Check it with a voltmeter and use the resistor only if necessary. Less than seven volts will result in a weak spark, and over ten volts will burn the points. Nearly all electronic ignitions require twelve volts (no resistor). This includes HEI, ACCEL, 41000 and 51000 series, and enhancer box systems (ACCEL 300+, Mallory HYFIRE®, MSD) an exception to this is the Mallory Unilite distributor when wired directly to the coil (no spark box). This required 7-9 volts supplied to coil positive. When using the supercoil with stock Chrysler or Ford Duraspark systems, use the ballast specified by the manufacturer...
Well, I am not running points, and my stock resistor is 1.5 ohm unit. So I went through my electricals stash and found a 0.7 ohm piece, plugged it in and to my astonishment the tach needle bounce went away...COMPLETELY!!!
This now started the "gears up top" turning...I figured I better check out the rest of the system to see what's going on because this result appears to suggest the coil was not seeing enough input V and subsequently the tach was not recognizing the signal.
Here are the readings, all taken while motor is running @ idle and using the '80 model year Diagnostic connector located on the fenderwall (just a quick and handy access to all the measurements):
1) 1.5 ohm resistor
BATT V = 14.23
Voltage Reg output = 7.60
Ignition V = 13.78
Coil Terminal V (using just the +/- as source) = 3.92 - 4.00
Coil Terminal + to GROUND V = 7.00
1) 0.7 ohm resistor
BATT V = 14.35
Voltage Reg output = 7.24-7.50
Ignition V = 13.76
Coil Terminal V (using just the +/- as source) = 6.10
Coil Terminal + to GROUND V = 9.80
So the coil Voltage increased, sure, it made sense since lower resistance value would do that.
I took the car for a ride and holy [censored], I could not believe it, there actually was a noticable difference in throttle response. Hard to give a quantitative assessment here, but you could actully feel this. This made me dig deeper. The Accel coil is a 12V coil, which as best as I can tell accepts 12V input at the coil terminals. Even now with the 0.7 ohm resistor I am still seeing only 9.80V, this begs the question: am I understanding this correctly, and should I be aiming to deliver 12V on the input terminals of the coil?
My next step is to try running this bypassing the resistor altogether...worth a try, but long-term I certainly do not want to fry the coil.
I'm curious what you guys are seeing?