Ignition Help

[chuckwp]

Trying to get a customer project car running.
35 V8 Flatty. Has a helmet type dist. that appears to be converted for an external coil.
The car will be 12 volts.
My question is-can I use an MSD coil with a ballast restior and is the wire comming from the dist. the coil neg. connection? Also, who is the maker of the conversion?

[corvette8n]

Not sure who makes the conversion, sold a lot of places. I took my conversion off and had a 6 volt coil rebuilt by Skip, plus I used a condensor sold by Tubman.
Search this forum for them. If all your grounds and wiring is good the 6 volt system works fine. Sorry I couldn't be of more help.

[flatheadmurre]

Don´t use any fancy coils on the helmet...you don´t need any ultra super high energy for a flathead...it will just be a higher chance for arcover and misery...my 2c
And i think skip can build the coil for 12v to if you want that...looks better works better...win win.

[JSeery]

Chuck, assume you know that the original vehicle is wired positive ground. No big deal, just something to keep in mind. If you wanted to, you could retain the setup the way it is. The issue with a high energy ignition on a flathead is the insulating components are often not up to it. A lot of flathead folks like that distributor (claimed to be one of the best Ford built), but I'm a bigger fan of the later pancake style. I prefer the looks and find them easier to work on. Either way, it is really necessary to have the distributor set up by someone that understands them and has a machine to do the job. There are several individuals here on the Barn that can set one up.

The wiring to the coil is the same as any normal coil, except you need to watch the polarity. On the positive ground systems the ignition connects to the (-) terminal on the coil and the (+) coil terminal connects to the distributor point and condenser. With a negative ground system all of this is reversed, ignition to the (+) coil terminal and coil (-) terminal to the points/condenser. So, when converting to 12v negative ground systems, the coil polarity needs to be switch to match.

[Charlie ny]

Chuck.....use a NAPA IC 14 coil....no resister required. Be sure to jump over or eliminate the under dash resister.

If neg ground be sure the wire coming from terminal on the adapter plate is connected to the negative terminal on the coil....if still pos ground the pos wire from the plate goes to the pos side of the coil.
Charlie ny

[chuckwp]

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Thanks all. Original coil long gone. Car is being rewired for 12 volt neg. ground. AAW harness alIready installed. I understand pos. vs. ground, just not familar with this set up. I will probably use Charlies suggestion for the Napa coil.

[JSeery]

Originally Posted by chuckwp

I will probably use Charlies suggestion for the Napa coil.

That coil is a good one. In case my last post was not clear, the connector on the adaptor in the photo you posted is the same as the wire on the side of a modern distributor than connects to the points and the condenser. A hint, the condensers available can be a problem, even new out of the box. So don't be surprised by having to go through several to find a good one.

[38bill]

Originally Posted by JSeery

Good one. In case my last post was not clear, the connector on the adaptor in the photo you posted is the same as the wire on the side of a modern distributor than connects to the points and the condenser. A hint, the condensers available can be a problem, even new out of the box. So don't be surprised by having to go through several to find a good one.

What JS said about condensers!


I helped a guy out at a car show with that type of conversion. His truck stalled just inside the gates. New conversion with new condenser. He just wouldn't believe me when I told him it was probably the condenser. Finally got him to try a spare I was carrying and it started right up. Moral of the story....start with a good quality condenser and carry a spare.

[tubman]

Originally Posted by flatheadmurre

Don´t use any fancy coils on the helmet...you don´t need any ultra super high energy for a flathead...it will just be a higher chance for arcover and misery...my 2c
And i think skip can build the coil for 12v to if you want that...looks better works better...win win.

I agree with Murre on this. If the secondary voltage is too high on what is essentially an ignition system designed 80 years ago, it will arc over to ground at the weakest point. I had an MSD on a flathead 25 years ago that would arc over at the coil tower on the distributor cap, while there was a recent thread on the "H.A.M.B." for a gentleman with a similar setup that was eating spark plugs. It is possible to have "too much of a good thing".

[Phil Gillespie]

Originally Posted by tubman

I agree with Murre on this. If the secondary voltage is too high on what is essentially an ignition system designed 80 years ago, it will arc over to ground at the weakest point. I had an MSD on a flathead 25 years ago that would arc over at the coil tower on the distributor cap, while there was a recent thread on the "H.A.M.B." for a gentleman with a similar setup that was eating spark plugs. It is possible to have "too much of a good thing".

A great place to go for a "Bullet Proof" robust condenser is with Tubman" Denny.
I have two of his units fitted at a flathead with the divers helmet distributor and one fitted with a crab distributor great products that look good mounted an engines.
Phil NZ

[40cpe]

Help me with this concern with high voltage coil: I have been under the impression that in a properly installed system the voltage only rises to the level needed to arc across the spark plug. If there is high resistance due to faulty plug wires, bad connections in the secondary side, wide plug gaps, etc, the spark will arc across at the weakest point of insulation. If my understanding is correct, the only down side of the HV coil is maybe more expensive.

On the OP's question of the use of the ballast resistor: A 12V system needs 3.0 (or maybe a little more) total resistance in the primary circuit. This would be a combination of the resistance between the + and - terminals and the ballast resistor. If the coil has 3 ohms resistance, there is no need for the ballast resistor.

[tubman]

The voltage put out by a coil is a function of the input voltage and the ratio of primary to secondary windings. How would it know how much voltage is needed to fire a plug? What about when a plug is slightly fouled and fires intermittently? Since it fires once in a while, it is not completely dead; does the coil know enough to raise the voltage on that one plug once in a while? How come it doesn't raise the voltage to what that plug needs? I think you had better re-think this.

On the MSD I installed, it was on a fresh engine where everything was new. I used marine surface gap spark plugs (which are designed for high-output ignition systems), so mine decided the coil tower on the cap was the point of least resistance. Believe, me, after replacing several caps the first year, I made damn sure there were no cracks and everything was squeaky clean. The guy on the "H.A.M.B." came there originally looking for Iridium spark plugs because his MSD was literally eating his plugs alive.

An ignition system is a carefully designed system, with all parts designed to work together in a balance. Upsetting that balance is looking for trouble. Most of the time we get away with it, but not always.

[JayChicago]

I think what 40cpe was meaning is the voltage as the coil discharges will rise until it jumps the spark plug gap. (I guess this is instantaneous, you would need a scope to see it rise) Any excess voltage put out by the coil will immediately go to ground across the plug gap, so shouldn't be a problem.

But as you point out, the spark plug is not always the point of least resistance. As you point out, too much voltage jumping the gap can cook the plugs; if you use a plug capable of withstanding the excess voltage, it will find an easier path to ground on these systems not designed for that high voltage.

[BUBBAS IGNITION]

You are correct !!!!!!

I have been under the impression that in a properly installed system the voltage only rises to the level needed to arc across the spark plug. If there is high resistance due to faulty plug wires, bad connections in the secondary side, wide plug gaps, etc, the spark will arc across at the weakest point of insulation. If my understanding is correct, the only down side of the HV coil is maybe more expensive.

The missing item here is a scope to properly measure the ignition voltage !!! You can have a high voltage coil ( marketing stuff) and ignition etc but if ya only have 7-1 compression etc it will only require the least amount of voltage. I used to teach a class on this using a spark plug into a glass chamber , i would use shop air and the spark would increase as i increased the air pressure . Thats what the old champion spark plug cleaners did when you looked into the glass and seen the spark, then turned the air pressure up to confirm that the plug would infact fire under compression.....
Most would be better off if they could just buy the decal (HI VOLTAGE) and put it on a stock coil !!!!!!

[BUBBAS IGNITION]

Save yer bucks !!!!!!

[38bill]

Originally Posted by BUBBAS IGNITION

Save yer bucks !!!!!!

And get one of those Bosh blue coils (no ballast resister required) that Bubba likes to use.

[chuckwp]

Originally Posted by 38bill

And get one of those Bosh blue coils (no ballast resister required) that Bubba likes to use.

Originally Posted by BUBBAS IGNITION

You are correct !!!!!!

I have been under the impression that in a properly installed system the voltage only rises to the level needed to arc across the spark plug. If there is high resistance due to faulty plug wires, bad connections in the secondary side, wide plug gaps, etc, the spark will arc across at the weakest point of insulation. If my understanding is correct, the only down side of the HV coil is maybe more expensive.

The missing item here is a scope to properly measure the ignition voltage !!! You can have a high voltage coil ( marketing stuff) and ignition etc but if ya only have 7-1 compression etc it will only require the least amount of voltage. I used to teach a class on this using a spark plug into a glass chamber , i would use shop air and the spark would increase as i increased the air pressure . Thats what the old champion spark plug cleaners did when you looked into the glass and seen the spark, then turned the air pressure up to confirm that the plug would infact fire under compression.....
Most would be better off if they could just buy the decal (HI VOLTAGE) and put it on a stock coil !!!!!!

Originally Posted by BUBBAS IGNITION

Save yer bucks !!!!!!

Thanks for all the info. Can you suggest a coil part number? We are going to use an external coil for now to try and get it running.

[chuckwp]

Originally Posted by chuckwp

Thanks for all the info. Can you suggest a coil part number? We are going to use an external coil for now to try and get it running.

OK, sorry, I saw what I wanted to know a few posts further up!

[Zeke3]

Re-read post #5 from CharlieNY for a recommendation.

[deuce_roadster]

Another place too much 2ndary voltage goes on a 37-41 helmet distributor is through the rotor to the shaft that runs through it.