Replacement coil on 86 205 V-6

We were out for the weekend the other week and I suddenly saw 15+ volts on the gauge. Being Saturday night, I hoped to pick up a new voltage regulator (checked and saw excess voltage at the batteries) on the Monday. Heading up-river the next day, the boat just cut out dead. No spark. Had a spare ignition module (Thunderbolt) and swapped that out. No spark. Left the boat tied to a dock at a trailer park and picked up a new voltage regulator on Monday. I'd had the alternator re-built a couple of yrs. ago, after it quit charging, and had assumed (wrongly, the reg. cost almost as much as the re-wind) all new parts. Swapped the volt. reg. and no dice. Realized I had kept the stock coil after changing out the ignition parts last summer. Presto, spark, and 14 volts. I'd been seeing 14.5 for a bit, and hadn't worried. as that's what my bikes charge at. Anyhow, I have an old coil of unknown age in my boat again. I had the option of spending 50 bucks (Canada) on an aftermarket stock coil, or getting a hotter coil for a bit more. I've bought a lower resistance 45,000 volt "flame-thrower" coil. Here's my question. I was told it is compatible with the Thunderbolt ignition, but am curious if anyone has any experience with changing from stock parts. I'm not expecting miracles from a hotter coil, but it would be nice to get a bit better fuel burn at lower RPM. Haven't messed with the plug gaps. Plug wires are new, quality wires, but nothing fancy. Distributor and pickup is new, 4bbl carb is rebuilt and motor has 20 hours on it after a re-build. Any thoughts on using a hotter coil, and anyone had a coil failure like mine? A couple of hours tops at 15.5 volts enough to fry it?

compatable meaning it doesent need a balast resistor. what is this regulator you mention. There usually in the alt itself ,not a seperate item.

Ion66 said:

the reg. cost almost as much as the re-wind) all new parts.

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wow- the regulator in the Delco SI is something like $4- you must have a Motorola alternator?
I wonder if you have a bad connection at the sensing terminal or something causing the alt to overcharge.
Or maybe a corroded ground to the alternator chassis. Or ground wire left off when replaced - that is common with Motorolas.

Ion66 said:

or getting a hotter coil for a bit more. I've bought a lower resistance 45,000 volt "flame-thrower" coil. Here's my question. I was told it is compatible with the Thunderbolt ignition, but am curious if anyone has any experience with changing from stock parts. I'm not expecting miracles from a hotter coil, but it would be nice to get a bit better fuel burn at lower RPM.

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here's the thing on these "hotter" coils:
The coil has nothing to do with voltage at the spark plugs. Like lightning, a spark jumps the gap and once it has jumped, it is done.
So, what determines the voltage required to jump the gap is the width of the gap (and fuel / air ratio). Stock plug gap will require about 8000 volts. It will never get any higher than 10,000V with a carb that is working right. Any coil can do that. When you put a hotter coil on, the voltage will not change.

So, if you buy a lamethrower it *might* be capable of jumping a wider gap if you re-gap your plugs, but that isn't recommended. It also might be better when plug wires start to break down or plugs are fouled. But it will also be better at jumping a pinhole in a plug wire to the block and cause a missfire. So imo, so called hotter coil is a waste. A heavy duty coil that does well vibrating on the engine is good. And that's a stock coil.

My issue with Lamethrower coils, is when you read the instructions 40 times and still have no idea if the thing requires an external resistor or not. It sorta says it does one place, then another it says no (kinda) There's probably a dozen threads where people have been asking that and the answers are always about a 50/50 split.

I'm not sure of the manufacturer of the alternator. The voltage regulator is a small, shiny aluminum box that is attached to the back of the alternator housing. There is no corrosion, and nothing obviously wrong when I took the alternator off and replaced the regulator. Hopefully I don't need a ballast with the coil! Will that cause any serious issues?

I used one on a 1995 4.3L and never noticed any difference. The one I used was epoxy filled.

guyjg said:

I used one on a 1995 4.3L and never noticed any difference. The one I used was epoxy filled.

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Good to know. I just wanted to put a new coil back in the boat and figured to swap for something a bit better than the old one. I didn't expect to see much if any difference since I'm not changing plug gap.

The stock TB-IV coil has less than one ohm of primary resistance....so any coil with a similar primary resistance will work....no resistance wire used in the engine harnesses with factory equipped TB-IV systems, so no ballast required.

2X on hystat's discussion on the "high voltage coils"; once the breakdown voltage of the combustion chamber's environment is reached, there is no more increase in the voltage at the plug...the real measure isn't the voltage of the spark but the energy in the spark....increase that and you may improve your 'burn'.