Duraspark resistor? - Vintage Mustang Forums
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post #1 of 16 (permalink) Old 08-08-2019, 10:51 AM Thread Starter
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Duraspark resistor?

I am working on a conversion, got the distributor, recurved,welded up the reluctor arm for less degrees of advance, installed the roller gear, got the blue module and all connectors. What I don't have is a resistor. Supposedly the "pink" resistance wire is 1.05 to 1.15 ohms. 1.1 nominally. Where do I get one of these? I see plenty of resistors for sale, but not in the specified range. I plan on running a stock coil but not locked down. Might consider aftermarket if I can purchase matched pair of coil and resistor suitable for ds2. Almost wish I went red box to avoid this hassle. Are ds2 distributors compatible with the ds1 (red grommet) box?
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post #2 of 16 (permalink) Old 08-08-2019, 12:12 PM
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Originally Posted by Mile68stang View Post
Almost wish I went red box to avoid this hassle. Are ds2 distributors compatible with the ds1 (red grommet) box?
Yes. Just match the box and coil. The resistor wire should be easily gotten though. https://www.npdlink.com/product/resi...1966&year=1966

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post #3 of 16 (permalink) Old 08-08-2019, 08:22 PM
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The pink resistor wire is built into the wiring harness under the dash. It connects to the red/green wire in the engine bay that went to the original coil.
http://averagejoerestoration.com/wp-...g-charging.jpg
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post #4 of 16 (permalink) Old 08-08-2019, 08:41 PM
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Use an epoxy coil for a 1985 Mustang 5.0 and no resistor is required.
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post #5 of 16 (permalink) Old 08-09-2019, 02:02 PM Thread Starter
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Use an epoxy coil for a 1985 Mustang 5.0 and no resistor is required.
With respect, the 85 used a oil filled coil, and a resistor wire in the harness. The resistor wire is the 1.1 ohms resistor that I am trying to replicate. If I want to go full power to a coil ( no resistor ) I would need to go to the red ignition module, or a HEI setup. Too many stories of red module burn out, and same with hei. I also want start retard
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post #6 of 16 (permalink) Old 08-09-2019, 08:22 PM
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With respect, the 85 used a oil filled coil, and a resistor wire in the harness.

1985 Mustang epoxy coil.
https://www.oreillyauto.com/detail/b...ion+coil&pos=2
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post #7 of 16 (permalink) Old 08-09-2019, 09:58 PM
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Mine had an epoxy coil, as does our '86. Bolted to the driver's shock tower.Both had a resistor in the wiring.

Last edited by GypsyR; 08-09-2019 at 10:00 PM.
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post #8 of 16 (permalink) Old 08-10-2019, 07:55 AM Thread Starter
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Originally Posted by Mile68stang View Post
With respect, the 85 used a oil filled coil, and a resistor wire in the harness.

1985 Mustang epoxy coil.
https://www.oreillyauto.com/detail/b...ion+coil&pos=2
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Originally Posted by GypsyR View Post
Mine had an epoxy coil, as does our '86. Bolted to the driver's shock tower.Both had a resistor in the wiring.


Thank you for responses, but I believe the coil you have a link to is inappropriate for my application. As I reviewed the " vehicle fitment" I saw it was intended for the 2v 302, and not the 4v 302. The 2v had fuel injection,(i didn't even know that they had fuel injection in 84 and 85) and completely different ignition system, and yes using full voltage coil. This ignition system is designed for that power, but using it on a ds2 would definitely burn out the module.
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post #9 of 16 (permalink) Old 08-10-2019, 09:35 AM
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I couldn't find a DuraSpark wiring harness at my local junk yard so I got a Painless harness to connect the distributor, module & coil. The kit included a ceramic resister as an option in case the harness in the car does not have a resister wire. As I have the original harness in the car, complete with the "pink" wire, it wasn't necessary. Be sure to have a full 12v to the module. I used the positive coil wire to trigger a relay for the 12v to the module.
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post #10 of 16 (permalink) Old 08-10-2019, 01:21 PM
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Quote:
Originally Posted by Mile68stang View Post
Thank you for responses, but I believe the coil you have a link to is inappropriate for my application. As I reviewed the " vehicle fitment" I saw it was intended for the 2v 302, and not the 4v 302. The 2v had fuel injection,(i didn't even know that they had fuel injection in 84 and 85) and completely different ignition system, and yes using full voltage coil. This ignition system is designed for that power, but using it on a ds2 would definitely burn out the module.
I don't know where you are getting your information from, but it is pretty skewed. If you look at the wiring diagrams for all 1985-1986 cars, no matter whether they are CFI, carbureted, 2.3, 3,8, or 5.0, they all have the resistor in line. The 1985 fuel injection was a throttle body version which was basically divorced from the ignition system and so that those engines had fuel injection made absolutely not one whit of difference. People have been swapping Duraspark ignitions into older cars for over 30 years now. They've pretty well have figured out what does and does not work these days, regardless of how Ford might have implemented this or that particular model/engine specific application. Many people here have not only done such Duraspark swaps, they have been running them successfully for years and years.
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post #11 of 16 (permalink) Old 08-10-2019, 06:49 PM
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I am using a MSD Ready-To-Run distributor, a Ford epoxy coil, no resistor of any kind, and my '65 runs just fine.
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post #12 of 16 (permalink) Old 08-10-2019, 10:52 PM Thread Starter
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I don't know where you are getting your information from, but it is pretty skewed. If you look at the wiring diagrams for all 1985-1986 cars, no matter whether they are CFI, carbureted, 2.3, 3,8, or 5.0, they all have the resistor in line. The 1985 fuel injection was a throttle body version which was basically divorced from the ignition system and so that those engines had fuel injection made absolutely not one whit of difference. People have been swapping Duraspark ignitions into older cars for over 30 years now. They've pretty well have figured out what does and does not work these days, regardless of how Ford might have implemented this or that particular model/engine specific application. Many people here have not only done such Duraspark swaps, they have been running them successfully for years and years.[/QUOTE]
GypsyR: My bad, sorry I accidentally included your quote with Texas. I agree with everything you say. The coil he suggested was a .7 ohms with no resistor. Given a system voltage of 14v, that coil would draw 20a. Way too much for the ds2, and it's limited fixed dwell. Stock resistor is 1.1 ohms, with coil of 1.17, for total of 2.27 ohms. Stock would only draw 6.16a. He's running a rtr msd, so of course he can run a low resistance coil at full current-it has some kind of dwell limiting or current limiting circuitry unlike my ds2. So, my apologies gypsyR.
That being said, can you give me any specific examples of resistor/coil combos that are known to work well?
In my 68, to match output on ds2 setup (2.27 ohms ), the resistor wire is 1.35 ohms. I need a coil of .92ohm. I couldn't find anything in that neighborhood. Closest I came up with was msd .8 ohm with 1.5 ohms petronix coil, coming in at 2.3 ohms total. Easily within the range of the factory coil/resistor ohm tolerance. My problem is this, is this acceptable? 14v ÷2.3ohm=6.09amp. Nice. But ....when you compare watts in stock system the 1.1 ohm resistor, produces 41w of heat. The 1.17 ohm coil receives 44.4 w. New system: 6.09 amp total. Volts=amps×resistance
Resistor = .8. So voltage drop=6.09×.8=4.872. 4.872v×6.09a=29.7w heat from resistor. Coil resistance =1.5. Vdrop =6.09×1.5=9.135v. 9.135v×6.09a=55w.
So with this setup I will be pumping 55w as opposed to 44w into the coil, while not overburdening the ds2 module(actually slightly less strain)

Is an extra 25% more energy into the coil TOO much? Will it cook it? Seems reasonable to me, but can anyone confirm?
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post #13 of 16 (permalink) Old 08-11-2019, 08:46 AM
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Not sure if this works but I posted the current draw and voltage at idle and at 4000rpm on this post https://forums.vintage-mustang.com/8880065-post37.html.

The duty cycle, freq,hertz or the on-off-on etc..... of the primary switching voltage changes and lowers the coil current demand compared to just dead heading the coil to ground and measuring. But bench testing for a shorted coil, your math works.

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post #14 of 16 (permalink) Old 08-11-2019, 10:47 AM
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Kind of overthinking it here, aren't we. Just with a stock Fox Duraspark ignition I've used one of those big old style Accel Super coils, an Accel TFI coil, stock Ford TFI, and MSD replacement TFI coils (two in service currently). I had an Accel TFI apparently die intermittently but didn't really troubleshoot it, I just grabbed another coil and found the problem to go away. I've used another Accel TFI and it gave no problems. Two is not even close to being a sample enough to make any kind of judgement on their quality. Suffice to say I've used a variety of these coils successfully on exactly the ignition system in question.

Truth is you could probably successfully use any good quality coil you like, as long as the primary resistance is between about .3 and 1.2 ohms. The stock Ford TFI is the value for the dollar at @30 kilowatts and 100 mj of output. The fancy MSD coils claim to add @10 kw and 20 mj on top of that which for all intensive purposes do nothing for a stock style Duraspark ignition. (Zero performance gain) They do have a bit of value when used with a multistrike CDI type ignition but they are different beasts.

Why am using MSD's? Why do I have an eight point roll bar in a street car that will never see a racetrack? Because I want to. I've never really liked the old oil-filled coils. Stock TFI coils are this dull black and MSD's are that snazzy high performance red that surely adds at least three horsepower just in looks. Plus a bonus extra horsepower if you put the MSD sticker on your car somewhere. So I hear.

.... it wouldn't be the first time reality took theory and conjecture out behind the woodshed and gave them a good thrashing.
I have some cars. With a long list of parts on them that if anyone was interested in, they'd ask.
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post #15 of 16 (permalink) Old 08-11-2019, 12:56 PM Thread Starter
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Originally Posted by GypsyR View Post
Kind of overthinking it here, aren't we. Just with a stock Fox Duraspark ignition I've used one of those big old style Accel Super coils, an Accel TFI coil, stock Ford TFI, and MSD replacement TFI coils (two in service currently). I had an Accel TFI apparently die intermittently but didn't really troubleshoot it, I just grabbed another coil and found the problem to go away. I've used another Accel TFI and it gave no problems. Two is not even close to being a sample enough to make any kind of judgement on their quality. Suffice to say I've used a variety of these coils successfully on exactly the ignition system in question.

Truth is you could probably successfully use any good quality coil you like, as long as the primary resistance is between about .3 and 1.2 ohms. The stock Ford TFI is the value for the dollar at @30 kilowatts and 100 mj of output. The fancy MSD coils claim to add @10 kw and 20 mj on top of that which for all intensive purposes do nothing for a stock style Duraspark ignition. (Zero performance gain) They do have a bit of value when used with a multistrike CDI type ignition but they are different beasts.

Why am using MSD's? Why do I have an eight point roll bar in a street car that will never see a racetrack? Because I want to. I've never really liked the old oil-filled coils. Stock TFI coils are this dull black and MSD's are that snazzy high performance red that surely adds at least three horsepower just in looks. Plus a bonus extra horsepower if you put the MSD sticker on your car somewhere. So I hear.



Yup, over thinking it. I am just going going to heed your advice and grab a coil as you said .3 to 1.2 range. I'll just get a backup box in case of burn out. Spent so much time reading and figuring, if traded for time working, I probably could have paid for complete msd system twice over. Typical me...dumbass trying to figure things out....lol. anyways, thank you and everyone else for your help!

Last edited by Mile68stang; 08-11-2019 at 12:59 PM.
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