The Stovebolt Site Forums The Shop Area Engine Shop "Flame Thrower Coils"

Hey Stove Bolt crew

I had a hard time starting my '51 3/4T ('62 235 motor), and the spark was crazy week, but I bought online this "Flame Thrower Coil" that is good for either 6 or 12V and the spark is actually decent and my truck is loads easier to start now.

Any thoughts on these coils and any concerns?

Some day might convert to 12V but for now (and the last 70 years) 6V seems to be fine.

Clem

P.T. Barnum is alive and well, and it appears that he's selling ignition parts these days! That coil should take a very short time to burn up a set of points, as it has approximately the same primary resistance as a coil used on a 12 volt HEI ignition system. A normal 6V coil has about 1.5 ohms or so of primary circuit resistance.
Jerry

The original 6V ignition with points and condenser will have a coil that can produce maybe a maximum 30,000 (30KV) volts but it only takes around 8-12KV to fire a stock spark plug under normal load.

If you want to buy a higher voltage coil, the manufacturer recommends to replace the stock points with their PerTronix Ignitors. You have to select the correct coil and ignitor for you engine and battery voltage (6 or 12 volts). If you want to use your stock points then you have to select the coil with the correct internal resistance. Even if you find a higher KV coil that doesn't burn up your points you also have to make sure your spark plug wires can take the extra KV. A plug wire can induce voltage into a nearby plug wire causing cross-firing...truck runs bad.

Here is a clipping from an article I read:

Choosing The Correct Ignition Coil.

For specific recommendations we contacted our pal, Don Lindfors, at PerTronix to get the straight story on coils. As he explains, PerTronix offers three oil-filled, canister-style coils and they are identified by the ignition system they are suited for:

The Flame Thrower 40,000V coils have internal resistance rated at 1.5 or 3.0 ohms. The 3.0-ohm coil should be used on PerTronix Ignitors installed on four- and six-cylinder engines while 1.5-ohm coils should be used for eight-cylinder applications. These coils can be used on virtually any inductive (non-capacitive discharge) ignition system.

Flame Thrower II coils have lower resistance, 0.6 ohms for use with Ignitor II ignition systems as well as many other high-energy ignitions. The low resistance helps to produce up to 45,000 V. This higher voltage allows larger spark plug gaps for added power and better fuel economy.

Flame-Thrower III coils were developed for use with the new Ignitor III electronics. The extremely low resistance of 0.32 ohms results in 45,000 V and a coil that charges to peak, current typically 30-70 percent faster the other coils. It should be noted that these coils are compatible with Ignitor III electronics only.

Flamethrower PLUS Pertronix- - - - - - -Barnum must have hired W.C. Fields to write his ad copy! LOL!

Mechanical points have a current capacity of approximately 5 amps, max. By using simple Ohm's law, a coil with 1.5 Ohms of resistance will flow a current of 4 amps, well within the capacity of conventional points. However- - - - -and this is important- - - -in a "6 volt" electrical system the voltage is not a constant. During cold cranking, a "6V" system will be operating at about 4.5-5 volts due to the load of the starter current on the battery. at 4.5 volts, the current through the above coil drops to 3 amps- - - -maybe resulting in a weak spark. At normal engine speed after starting, the system voltage will be approximately 7.5 to allow for good battery charging. That divides out to 5 amps- - - -right at maximum capacity for the points.

All the above assumes that a coil primary is a static environment, which it's not, Upon initial closing of the points they see a situation approaching a dead short until the magnetic field inside the coil begins to produce a phenomenon known as "inductive reactance" which tends to limit the current flow as the magnetism continues to build up. That reactance, along with the straight resistance of the primary winding combines to limit the current flow to an acceptable maximum to minimize point burning. In a 6 cylinder engine running at 2K RPM, the above situation is happening 100 times every second. We haven't even begun to consider the induced voltage in the primary as the points open and the magnetic field collapses, which can be 50 volts or more. That's why a condenser (capacitor) is needed to shunt the voltage surge away from the points and prevent flashover and metal transfer at the points upon opening.

Most of the people who tinker with the ignition circuit that was designed to work properly by the engineers who developed it don't have a clue what's actually going on.

P.T. Barnum- - - - -"There's a sucker born every minute!"

W.C, Fields- - - - -"Never give a sucker an even break!"

Jerry

I always used Bosch 6 volt flame thrower type coil. It came with the Porsche Hot Shot Kit. I used it on Porsche and modified VW's. It may still be available from Bosch. Doc.

The part I don't like is the lack of good head's up Pertronix information to help you make a sensible purchase. Also, voltage potential is needed to initiate the spark across the plug gap but it's the current that produces the spark energy. Nobody advertises the current capability.

Clem, there is typical old-style maintenance involved if you keep your Stovebolt original. When starting a cold motor (stock coil and 6 volt battery) the battery current is literally sucked into the starter motor (I don't know maybe 300 amps) and at the same time you need some of this current energy for the plugs. A weak battery doesn't help at all. Then it's a series of resistances that limits the current energy to the spark plugs. Poor battery connections, small diameter battery cables, poor grade of copper in the battery cables, poor connections on the wiring going to the coil primary can reduce the capability of the coil to build up a strong field. From the coil secondary, humidity inside the distributor, worn points, corroded rotor cap, corroded cap posts, bad cap to spark plug wire connections, spark wires with bad insulation (bad wires) are some of the "roadblocks" to getting current to the plugs. All this leads up to my point. Just because you have weak spark doesn't mean the coil is bad or needs to be a higher voltage. I would look for things that typically wear out first.

Why do manufacturers always brag about the open circuit voltage capabilities of their coils? Once a clean, properly gapped spark plug ionizes the gap at around 8K-10K volts, it's impossible for the coil to build up any more voltage- - - - -whether its open-circuit capability is 20KV or 500KV. The current flow across the plug gap remains constant, and the induced voltage in the coil secondary winding CANNOT rise above the point where the spark begins to flow across the gap.
Jerry

First let me start by saying I am not a engineer, or a scientist, or a retired shop teacher. I am just a guy who loves old GM trucks and the GM six cylinder engine.

I have put 13k on my 45 GMC truck that has both Petronix and the flame thrower coil. At first I ran just a regular stock coil and stock plug wires. Yes, I am also using the pertonix plug wires now too. When I first bought the truck, the prior owner had already installed the Pertronix, and I was not amused by the thought of having it, hearing negitive storys about Pertonix through the years. In the past I had always ran the stock points set up in my previous trucks. Also at the time I was in the process of setting up my 1949 GMC suburban chassis that has a GMC 270 in it and I had already set it up with stock points.

While chasing a stumble under load in the 45 GMC a few years back I worked my way around the truck ignition system completely, and during that process I swapped out the Pertronix back to points and ran the truck. It was a noticable difference. Faster starting with the Pertronix and overall the truck feels like it has more pep during the rpm range when I run it. The prior owner of the truck put around 15k on the truck with the Pertronix before I owned it. So that's roughly 28k trouble free miles on the pertonix system in this truck.

I have since changed out the points on my suburban to a complete Pertonix set up. Again, I have notived a change for the better.


Here is a good article to read about Pertronix verses points ;

https://www.hagerty.com/media/maintenance-and-tech/ignition-debate-points-vs-pertronix/



Hot Rod, are you implying that Pertonix is falsley selling products? I'm curious as to why you make comments like "Flamethrower PLUS Pertronix- - - - - - -Barnum must have hired W.C. Fields to write his ad copy! LOL!"

And also "P.T. Barnum- - - - -"There's a sucker born every minute!"

W.C, Fields- - - - -"Never give a sucker an even break!"

So if these two guys are wrting the adds for Pertonix to sell their products your implying its fraudulent?


To bring it back full circle, my overall opinion is to run the complete set up from start to finish. Pertronix, coil, and plug wires. I would not recommend running the flame thrower coil with the stock points set up.

I am saying that for the people who want an electronic ignition, there are better ways to accomplish that goal than to use a system with proprietary components and a well-documented history of catastrophic failures. General Motors, Ford, Chrysler, and a bunch of foreign manufacturers have developed "point-less" ignition systems that can be adapted to a stovebolt engine, all of which are better-engineered and more reliable than Pertronix. Anyone who is willing to take a chance on the possibility of getting stranded out on the road somewhere is free to do so, but they need to be forewarned before spending their money. If your system satisfies you, I'm deliriously happy for you. Even at age 75 and with a badly compromised left leg from a motorcycle wreck, I think I could outrun anybody who tried to GIVE me a Pertronix ignition system, let alone spend any money on one. Opinions are like "noses"- - - -everybody's got one, and some of them can be pretty "smelly".
Jerry

So, I need a fatter spark, and the 0.6 I know understand will eat my points, no bueno
But should I get a stock coil from The Truck Shop in OC for $24, or should I go on ebay and get the Pertronix 40511 Flame-Thrower Coil 40,000 Volt 3.0 ohm Black for $40. Will it generate that much of a better spark, and not eat my points?

Thanks for the review everyone, I have a good Optima Battery with a steady 6.2 volts, new cables from the parts store, I resurfaced the frame so no rust and good contact. I even have a rebuilt starter.

Will there be a good balance, better starting spark that will start my truck easily and not eat points....?
-Clem

There's a simpler way to get a hot spark for starting, and save the points. Just install the same type of ballast resistor system that the 12V ignition systems use, and retro-fit the starter with a foot switch that has the small side terminal to bypass the resistor during startup. Use a 1 ohm 200 watt wire-wound resistor in series with the ignition switch and bypass it during starting with the side terminal of the start switch wired directly to the coil. That will avoid spending any more money unnecessarily on another trick coil, and still give you the hot spark boost during startup that you apparently think you need. Does anybody really believe Pertronix actually makes their own coils?
Jerry

Question for the pertronix experts. I ran accros this thread looking for answers to something totaly diffrent but it caught my attention . My conern is this. I recently had my points changed out to pertronix on my 1951 216 12V . The mechanic that did the job did not change out the stock coil or the spark plug wires. Is it necessary to install the pertronix flame thrower along with the pertronix wires ? And if so does the gap on the spark plugs need to be changed from the recomended gap when using points ? Also does the timing need to be reajusted? I guess a simpler question is can i swap the stock coil to flame thrower and the spark plug wires to the pertronix wires to mach the pertronix ignition without having to mess with the timing and the spark plug gap and is all this even necessary?

First, I’m not a Pertronix expert but I did stay in a Holiday Inn once. Any time you go to electronic ignition the spark plug gap must be increased. I think Pertronix recommends .045. No metal core plug wires. The coil does not have to be changed. Timing will be fine right where it is. All that being said your experience may differ, as several of our members have found out, but my personal experience with the product is it is purely unreliable garbage. As I said your experience may be different.

This is to answer Clem's last question:

Buy a stock coil if you plan to use points.

Optima batteries have had a reliability problem in the past. I hope that this has been resolved by now.

You said "new cables" then "resurfaced frame".
If you are talking about battery cables make sure you have at minimum 2/0 gauge (also called 00 AWG) pure copper (not copper clad) cables for your 6 volt system.

I've installed several Pertronix units with no issues over the last 15 years. Cannot use spark plug wires with metal wire, but can usually keep your stock coil. There may also be instructions that if your vehicle uses a ballast resistor that you may not need it with the Pertronix unit.

Make sure all battery connections are good including all grounds.

I find this set up usually runs best in tune at 8 to 12 degrees advanced.

Clem before spending a lot on after market ignition consider an HEI out of a 292 chevy. Now I understand if you want an original look that wont work,and you will need to go to 12 volt. If it might work for you ,you'll soon find out it makes a real engine out of any version ! just bump it it's running ! Now I half to qualify that my whle fleet (8 units) are on propane. Also you can do it on gasoline too. Best thing about propane it's NEVER cold natured and there is no choke to fight. Just a thought